User manual D-LINK DGS-3308TG

DGS-3308 Series 8-Port Gigabit Layer 3 Switch User's Guide First Edition (December 2001) 651FG3308015 Printed In Taiwan RECYCLABLE Wichtige Sicherheitshinweise 1. 2. 3. 4. 5. 6. 7. 8. 9. Bitte lesen Sie sich diese Hinweise sorgfältig durch. Heben Sie diese Anleitung für den spätern Gebrauch auf. Vor jedem Reinigen ist das Gerät vom Stromnetz zu trennen. Vervenden Sie keine Flüssig- oder Aerosolreiniger. Am besten dient ein angefeuchtetes Tuch zur Reinigung. Um eine Beschädigung des Gerätes zu vermeiden sollten Sie nur Zubehörteile verwenden, die vom Hersteller zugelassen sind. Das Gerät is vor Feuchtigkeit zu schützen. Bei der Aufstellung des Gerätes ist auf sichern Stand zu achten. Ein Kippen oder Fallen könnte Verletzungen hervorrufen. Verwenden Sie nur sichere Standorte und beachten Sie die Aufstellhinweise des Herstellers. Die Belüftungsöffnungen dienen zur Luftzirkulation die das Gerät vor Überhitzung schützt. Sorgen Sie dafür, daß diese Öffnungen nicht abgedeckt werden. Beachten Sie beim Anschluß an das Stromnetz die Anschlußwerte. Die Netzanschlußsteckdose muß aus Gründen der elektrischen Sicherheit einen Schutzleiterkontakt haben. 10. Verlegen Sie die Netzanschlußleitung so, daß niemand darüber fallen kann. Es sollete auch nichts auf der Leitung abgestellt werden. 11. Alle Hinweise und Warnungen die sich am Geräten befinden sind zu beachten. 12. Wird das Gerät über einen längeren Zeitraum nicht benutzt, sollten Sie es vom Stromnetz trennen. Beschädigung vermieden. 13. Durch die Lüftungsöffnungen dürfen niemals Gegenstände oder Flüssigkeiten in das Gerät gelangen. Dies könnte einen Brand bzw. Elektrischen Schlag auslösen. 14. Öffnen Sie niemals das Gerät. Das Gerät darf aus Gründen der elektrischen Sicherheit nur von authorisiertem Servicepersonal geöffnet werden. 15. Wenn folgende Situationen auftreten ist das Gerät vom Stromnetz zu trennen und von einer qualifizierten Servicestelle zu überprüfen: a ­ Netzkabel oder Netzstecker sint beschädigt. b ­ Flüssigkeit ist in das Gerät eingedrungen. c ­ Das Gerät war Feuchtigkeit ausgesetzt. d ­ Wenn das Gerät nicht der Bedienungsanleitung ensprechend funktioniert oder Sie mit Hilfe dieser Anleitung keine Verbesserung erzielen. e ­ Das Gerät ist gefallen und/oder das Gehäuse ist beschädigt. f ­ Wenn das Gerät deutliche Anzeichen eines Defektes aufweist. 16. Bei Reparaturen dürfen nur Orginalersatzteile bzw. den Orginalteilen entsprechende Teile verwendet werden. Der Einsatz von ungeeigneten Ersatzteilen kann eine weitere Beschädigung hervorrufen. 17. Wenden Sie sich mit allen Fragen die Service und Repartur betreffen an Ihren Servicepartner. Somit stellen Sie die Betriebssicherheit des Gerätes sicher. 18. Zum Netzanschluß dieses Gerätes ist eine geprüfte Leitung zu verwenden, Für einen Nennstrom bis 6A und einem Gerätegewicht gr ßer 3kg ist eine Leitung nicht leichter als H05VV-F, 3G, 0.75mm2 einzusetzen. Somit wird im Falle einer Überspannung eine WARRANTIES EXCLUSIVE IF THE D-LINK PRODUCT DOES NOT OPERATE AS WARRANTED ABOVE, THE CUSTOMER'S SOLE REMEDY SHALL BE, AT D-LINK'S OPTION, REPAIR OR REPLACEMENT. THE FOREGOING WARRANTIES AND REMEDIES ARE EXCLUSIVE AND ARE IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, EITHER IN FACT OR BY OPERATION OF LAW, STATUTORY OR OTHERWISE, INCLUDING WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. D-LINK NEITHER ASSUMES NOR AUTHORIZES ANY OTHER PERSON TO ASSUME FOR IT ANY OTHER LIABILITY IN CONNECTION WITH THE SALE, INSTALLATION MAINTENANCE OR USE OF D-LINK'S PRODUCTS D-LINK SHALL NOT BE LIABLE UNDER THIS WARRANTY IF ITS TESTING AND EXAMINATION DISCLOSE THAT THE ALLEGED DEFECT IN THE PRODUCT DOES NOT EXIST OR WAS CAUSED BY THE CUSTOMER'S OR ANY THIRD PERSON'S MISUSE, NEGLECT, IMPROPER INSTALLATION OR TESTING, UNAUTHORIZED ATTEMPTS TO REPAIR, OR ANY OTHER CAUSE BEYOND THE RANGE OF THE INTENDE D USE, OR BY ACCIDENT, FIRE, LIGHTNING OR OTHER HAZARD. LIMITATION OF LIABILITY IN NO EVENT WILL D-LINK BE LIABLE FOR ANY DAMAGES, INCLUDING LOSS OF DATA, LOSS OF PROFITS, COST OF COVER OR OTHER INCIDENTAL, CONSEQUENTIAL OR INDIRECT DAMAGES ARISING OUT THE INSTALLATION, MAINTENANCE, USE, PERFORMANCE, FAILURE OR INTERRUPTION OF A D- LINK PRODUCT, HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY. THIS LIMITATION WILL APPLY EVEN IF DLINK HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. IF YOU PURCHASED A D-LINK PRODUCT IN THE UNITED STATES, SOME STATES DO NOT ALLOW THE LIMITATION OR EXCLUSION OF LIABILITY FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES, SO THE ABOVE LIMITATION MAY NOT APPLY TO YOU. Limited Warranty Hardware: D-Link warrants each of its hardware products to be free from defects in workmanship and materials under normal use and service for a period commencing on the date of purchase from D-Link or its Authorized Reseller and extending for the length of time stipulated by the Authorized Reseller or D-Link Branch Office nearest to the place of purchase. This Warranty applies on the condition that the product Registration Card is filled out and returned to a D-Link office within ninety (90) days of purchase. A list of D-Link offices is provided at the back of this manual, together with a copy of the Registration Card. If the product proves defective within the applicable warranty period, D-Link will provide repair or replacement of the product. D-Link shall have the sole discretion whether to repair or replace, and replacement product may be new or reconditioned. Replacement product shall be of equivalent or better specifications, relative to the defective product, but need not be identical. Any product or part repaired by D-Link pursuant to this warrant y shall have a warranty period of not less than 90 days, from date of such repair, irrespective of any earlier expiration of original warranty period. When D-Link provides replacement, then the defective product becomes the property of D-Link. Warranty se rvice may be obtained by contacting a D-Link office within the applicable warranty period, and requesting a Return Material Authorization (RMA) number. If a Registration Card for the product in question has not been returned to D-Link, then a proof of pur chase (such as a copy of the dated purchase invoice) must be provided. If Purchaser's circumstances require special handling of warranty correction, then at the time of requesting RMA number, Purchaser may also propose special procedure as may be suitable to the case. After an RMA number is issued, the defective product must be packaged securely in the original or other suitable shipping package to ensure that it will not be damaged in transit, and the RMA number must be prominently marked on the outside of the package. The package must be mailed or otherwise shipped to D-Link with all costs of mailing/shipping/insurance prepaid. D-Link shall never be responsible for any software, firmware, information, or memory data of Purchaser contained in, stored on, or integrated with any product returned to D-Link pursuant to this warranty. Any package returned to D-Link without an RMA number will be rejected and shipped back to Purchaser at Purchaser's expense, and D-Link reserves the right in such a case to levy a reasonable handling charge in addition mailing or shipping costs. Software: Warranty service for software products may be obtained by contacting a D-Link office within the applicable warranty period. A list of D-Link offices is provided at the back of thi s manual, together with a copy of the Registration Card. If a Registration Card for the product in question has not been returned to a D-Link office, then a proof of purchase (such as a copy of the dated purchase invoice) must be provided when requesting warranty service. The term "purchase" in this software warranty refers to the purchase transaction and resulting license to use such software. D-Link warrants that its software products will perform in substantial conformance with the applicable product documentation provided by D-Link with such software product, for a period of ninety (90) days from the date of purchase from D-Link or its Authorized Reseller. D-Link warrants the magnetic media, on which D-Link provides its software product, against failure during the same warranty period. This warranty applies to purchased software, and to replacement software provided by D-Link pursuant to this warranty, but shall not apply to any update or replacement which may be provided for download via the Internet, or to any update which may otherwise be provided free of charge. D-Link's sole obligation under this software warranty shall be to replace any defective software product with product which substantially conforms to D-Link's applicable product documentation. Purchaser assumes responsibility for the selection of appropriate application and system/platform software and associated reference materials. D-Link makes no warranty that its software products will work in combination with any hardware, or any application or system/platform software product provided by any third party, excepting only such products as are expressly represented, in D-Link's applicable product documentation as being compatible. D-Link's obligation under this warranty shall be a reasonable effort to provide compatibility, but D-Link shall have no obligation to provide compatibility when there is fault in the third-party hardware or software. D-Link makes no warranty that operation of its software products will be uninterrupted or absolutely error-free, and no warranty that all defects in the software product, within or without the scope of D-Link's applicable product documentation, will be corrected. D-Link Offices for Registration and Warranty Service The product's Registration Card, provided at the back of this manual, must be sent to a D-Link office. To obtain an RMA number for warranty service as to a hardware product, or to obtain warranty service as to a software product, contact the D-Link office nearest you. An address/telepho ne/fax/e-mail/Web site list of D-Link offices is provided in the back of this manual. Trademarks Copyright ©2001 D-Link Corporation. Contents subject to change without prior notice. D-Link is a registered trademark of D-Link Corporation/D-Link Systems, Inc. All other trademarks belong to their respective proprietors. Copyright Statement No part of this publication may be reproduced in any form or by any means or used to make any derivative such as translation, transformation, or adaptation without permission from D-Link Corporation/D-Link Systems Inc., as stipulated by the United States Copyright Act of 1976. FCC Warning This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with this user's guide, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his own expense. CE Mark Warning This is a Class A product. In a domestic environment, this product may cause radio interference in which case the user may be required to take adequate measures. VCCI Warning BSMI Warning Table of Contents About This Guide...............................................................................................................................................................................................1 Overview of this User's Guide .....................................................................................................................................................................1 Introduction.........................................................................................................................................................................................................2 Layer 3 Switching...........................................................................................................................................................................................2 The Functions of a Layer 3 Switch..........................................................................................................................................................3 Features ...........................................................................................................................................................................................................3 Ports...............................................................................................................................................................................................................3 Performance Features...................................................................................................................................................................................4 Layer 2 Switching Features......................................................................................................................................................................4 Layer 3 Switching Features......................................................................................................................................................................4 Traffic Classification and Prioritization...............................................................................................................................................5 Management ................................................................................................................................................................................................5 Optional Redundant Power Supply........................................................................................................................................................6 Fast Ethernet Technology.............................................................................................................................................................................6 Gigabit Ethernet Technology .......................................................................................................................................................................6 Unpacking and Setup........................................................................................................................................................................................7 Unpacking........................................................................................................................................................................................................7 Installation......................................................................................................................................................................................................7 Desktop or Shelf Installation...................................................................................................................................................................7 Rack Installation ........................................................................................................................................................................................8 Power on...........................................................................................................................................................................................................9 Power Failure...............................................................................................................................................................................................9 Identifying External Components ................................................................................................................................................................10 Front Panel....................................................................................................................................................................................................10 Rear Panel .....................................................................................................................................................................................................10 Side Panels....................................................................................................................................................................................................11 LED Indicators..............................................................................................................................................................................................11 Connecting The Switch ...................................................................................................................................................................................12 PC to Switch..................................................................................................................................................................................................12 Switch to Switch (other devices) ...............................................................................................................................................................12 Switch Management and Operating Concepts..........................................................................................................................................14 Local Console Management ...................................................................................................................................................................14 IP Addresses and SNMP Community Names ...................................................................................................................................15 Traps............................................................................................................................................................................................................16 MIBs ............................................................................................................................................................................................................17 SNMP..........................................................................................................................................................................................................17 Packet Forwarding....................................................................................................................................................................................18 MAC Address Aging Time......................................................................................................................................................................18 Filtering ......................................................................................................................................................................................................18 IP Addressing and Subnetting...............................................................................................................................................................19 802.1Q VLANs .........................................................................................................................................................................................23 Spanning Tree Protocol............................................................................................................................................................................28 Internet Protocols......................................................................................................................................................................................34 The Domain Name System.....................................................................................................................................................................42 DHCP Servers............................................................................................................................................................................................42 Routing........................................................................................................................................................................................................42 ARP..............................................................................................................................................................................................................43 Multicasting...............................................................................................................................................................................................43 Internet Group Management Protocol (IGMP)...................................................................................................................................45 Multicast Routing Algorithms...............................................................................................................................................................46 Multicast Routing Protocols...................................................................................................................................................................48 Routing Protocols......................................................................................................................................................................................48 Configuring the Switch Using the Console Interface ...............................................................................................................................54 Before You Start ...........................................................................................................................................................................................54 General Deployment Strategy................................................................................................................................................................54 VLAN Layout ............................................................................................................................................................................................55 Assigning IP Network Addresses and Subnet Masks to VLANs ..................................................................................................55 Defining Static Routes.............................................................................................................................................................................55 Connecting to the Switch............................................................................................................................................................................56 Console Usage Conventions ...................................................................................................................................................................56 Setup User Accounts ...................................................................................................................................................................................58 User Accounts Management ..................................................................................................................................................................59 Save Changes................................................................................................................................................................................................60 Reboot.............................................................................................................................................................................................................62 Logging Onto The Switch Console ............................................................................................................................................................63 Updating or Deleting User Accounts....................................................................................................................................................63 Viewing Current User Accounts............................................................................................................................................................64 Deleting a User Account ..........................................................................................................................................................................65 Setting Up The Switch................................................................................................................................................................................65 Basic Setup ................................................................................................................................................................................................65 Switch Information...................................................................................................................................................................................66 IP Setup.......................................................................................................................................................................................................67 Remote Management Setup...................................................................................................................................................................69 Configure Ports..........................................................................................................................................................................................70 Serial Port Settings..................................................................................................................................................................................71 Switch Operation Mode ..............................................................................................................................................................................72 Changing the Switch Operation Mode .................................................................................................................................................72 Layer 2 Switch Settings ..........................................................................................................................................................................75 Layer 3 Switch Mode - Setup RIP .........................................................................................................................................................76 Advanced Setup............................................................................................................................................................................................78 Configuring VLANs..................................................................................................................................................................................78 VLANs by Switch Operating Mode ­ Layer 2 Only and IP Routing..............................................................................................78 Setting Up IP Interfaces .............................................................................................................................................................................85 Multicasting..................................................................................................................................................................................................88 Layer 2 Multicast Setup .........................................................................................................................................................................88 IGMP Snooping Settings ­ by VLAN...................................................................................................................................................88 IEEE 802.1Q Multicast Forwarding .....................................................................................................................................................90 Static Router Port.....................................................................................................................................................................................91 Layer 3 Multicasting................................................................................................................................................................................92 Static Router Port.....................................................................................................................................................................................98 Mirroring..................................................................................................................................................................................................... 100 Priority......................................................................................................................................................................................................... 102 Filtering....................................................................................................................................................................................................... 103 Layer 2 Filtering .................................................................................................................................................................................... 103 Layer 3 (IP Routing) Filtering............................................................................................................................................................. 104 Forwarding.................................................................................................................................................................................................. 107 Layer 2 Forwarding ............................................................................................................................................................................... 107 IP Routing Forwarding.......................................................................................................................................................................... 108 MAC Address Forwarding................................................................................................................................................................... 108 Spanning Tree............................................................................................................................................................................................ 111 Switch Spanning Tree Settings .......................................................................................................................................................... 111 Port Group Spanning Tree Settings................................................................................................................................................... 113 Port Trunking............................................................................................................................................................................................. 114 Switch Utilities ......................................................................................................................................................................................... 116 Layer 2 Switch Utilities....................................................................................................................................................................... 116 Upgrade Firmware from TFTP Server.............................................................................................................................................. 116 Download Configuration File from TFTP Server............................................................................................................................ 117 Upload Configuration File to TFTP Server...................................................................................................................................... 118 Save Log to TFTP Server...................................................................................................................................................................... 119 Ping ........................................................................................................................................................................................................... 120 Layer 3 Utilities..................................................................................................................................................................................... 120 BOOTP/DHCP Relay............................................................................................................................................................................. 120 DNS Relay............................................................................................................................................................................................... 122 Network Monitoring ................................................................................................................................................................................. 124 Layer 2 Network Monitoring............................................................................................................................................................... 124 Port Utilization...................................................................................................................................................................................... 125 Port Error Packets ................................................................................................................................................................................. 126 Port Packet Analysis Table................................................................................................................................................................. 126 MAC Address Forwarding Table ....................................................................................................................................................... 127 IGMP Snooping....................................................................................................................................................................................... 128 Switch History........................................................................................................................................................................................ 129 Layer 3 Network Monitoring............................................................................................................................................................... 130 Browse IP Address................................................................................................................................................................................. 130 IP Routing Table .................................................................................................................................................................................... 131 ARP Table ............................................................................................................................................................................................... 132 Browse Router Port ............................................................................................................................................................................... 133 IP Multicast Forwarding Table .......................................................................................................................................................... 134 IGMP Group Table................................................................................................................................................................................. 135 DVMRP Routing Table ........................................................................................................................................................................ 136 Reboot and Factory Reset ....................................................................................................................................................................... 137 Web-Based Network Management........................................................................................................................................................... 140 Introduction ................................................................................................................................................................................................ 140 Before You Start ........................................................................................................................................................................................ 140 General Deployment Strategy............................................................................................................................................................. 140 VLAN Layout ......................................................................................................................................................................................... 141 Assigning IP Network Addresses and Subnet Masks to VLANs ............................................................................................... 141 Defining Static Routes.......................................................................................................................................................................... 141 Getting Started.......................................................................................................................................................................................... 142 Configuring the Switch............................................................................................................................................................................. 142 User Accounts Management ............................................................................................................................................................... 142 Saving Changes...................................................................................................................................................................................... 144 Factory Reset.......................................................................................................................................................................................... 144 Using Web-Based Management ............................................................................................................................................................ 145 Configuration ............................................................................................................................................................................................. 148 Switch IP Setup...................................................................................................................................................................................... 153 Switch Information................................................................................................................................................................................ 153 Power Supply & Cooling Fan Status ................................................................................................................................................. 154 Configure Ports....................................................................................................................................................................................... 155 Switch Settings ...................................................................................................................................................................................... 156 Configure Layer 3 - IP Networking..................................................................................................................................................... 157 VLANs ..................................................................................................................................................................................................... 160 Multicasting............................................................................................................................................................................................ 163 Priority..................................................................................................................................................................................................... 169 Mirroring.................................................................................................................................................................................................. 170 Spanning Tree Protocol......................................................................................................................................................................... 172 Port Trunking.......................................................................................................................................................................................... 176 Forwarding .............................................................................................................................................................................................. 177 Filtering ................................................................................................................................................................................................... 180 BOOTP/DHCP Relay............................................................................................................................................................................. 182 DNS Relay............................................................................................................................................................................................... 184 Remote Management Setup................................................................................................................................................................... 185 Management Station IP Settings ...................................................................................................................................................... 185 SNMP Community Settings ............................................................................................................................................................... 186 Setup Trap Receivers ............................................................................................................................................................................ 187 Setup User Accounts............................................................................................................................................................................. 187 Serial Port Settings............................................................................................................................................................................... 189 Network Monitoring ................................................................................................................................................................................. 190 Statistics ................................................................................................................................................................................................. 190 Address Table......................................................................................................................................................................................... 194 Applications ............................................................................................................................................................................................ 198 Maintenance............................................................................................................................................................................................... 202 Upgrade Firmware from TFTP Server.............................................................................................................................................. 203 Download Configuration File from TFTP Server............................................................................................................................ 203 Upload Configuration File to TFTP Server...................................................................................................................................... 203 Save Log to TFTP Server...................................................................................................................................................................... 204 Save Changes.......................................................................................................................................................................................... 204 Factory Reset.......................................................................................................................................................................................... 205 Restart System ...................................................................................................................................................................................... 206 Technical Specifications .............................................................................................................................................................................. 207 RJ-45 Pin Specification............................................................................................................................................................................... 210 Runtime Switching Software Default Settings...................................................................................................................................... 211 Understanding and Troubleshooting the Spanning Tree Protocol..................................................................................................... 212 Blocking State ........................................................................................................................................................................................ 212 Listening State....................................................................................................................................................................................... 213 Learning State........................................................................................................................................................................................ 214 Forwarding State................................................................................................................................................................................... 214 Disabled State........................................................................................................................................................................................ 215 Troubleshooting STP................................................................................................................................................................................ 216 Spanning Tree Protocol Failure.......................................................................................................................................................... 216 Full/Half Duplex Mismatch................................................................................................................................................................. 217 Unidirectional Link............................................................................................................................................................................... 218 Packet Corruption.................................................................................................................................................................................. 218 Resource Errors ...................................................................................................................................................................................... 218 Identifying a Data Loop........................................................................................................................................................................ 219 Avoiding Trouble.................................................................................................................................................................................... 219 Brief Review of Bitwise Logical Operations ........................................................................................................................................... 223 Index................................................................................................................................................................................................................. 224 8-port Gigabit Ethernet Switch User's Guide ABOUT THIS GUIDE This User's guide tells you how to install your DGS-3308, how to connect it to your Ethernet network, and how to set its configuration using either the built-in console interface or Web-based management. Overview of this User's Guide · · · · · · · · · · · · Chapter 1, "Introduction." Describes the Switch and its features. Chapter 2, "Unpacking and Setup." Helps you get started with the basic installation of the Switch. Chapter 3, "Identifying External Components." Describes the front panel, rear panel, and LED indicators of the Switch. Chapter 4, "Connecting the Switch." Tells how you can connect the Switch to your Ethernet network. Chapter 5, "Switch Management and Operating Concepts." Talks about Local Console Management via the RS-232 DCE console port and other aspects about how to manage the Switch. Chapter 6, "Using the Console Interface." Tells how to use the built-in console interface to change, set, and monitor Switch performance and security. Chapter 7, "Web-Based Network Management." Tells how to manage the Switch through an Internet browser. Appendix A, "Technical Specifications." Lists the technical specifications of the DGS-3308TG and DGS-3308FG. Appendix B, "RJ-45 Pin Specifications." Shows the details and pin assignments for the RJ-45 receptacle/connector. Appendix C, "Factory Default Settings." Appendix D, "Understanding and Troubleshooting the Spanning Tree Protocol." Appendix E, "Brief Review of Bitwise Logical Operations." 1 8-port Gigabit Ethernet Switch User's Guide 1 INTRODUCTION This section describes the Layer 3 functionality and Layer 2 and Layer 3 features of the DGS-3308 Series switches. Some background information about Ethernet/Fast Ethernet, Gigabit Ethernet, and switching technology is presented. This is intended for readers who may not be familiar with the concepts of layered switching and routing but is not intended to be a complete or in-depth discussion. For a more detailed discussion of the functionality of the DGS-3308, please see Chapter 5, "Switch Management and Operating Concepts." Layer 3 Switching Layer 3 switching is the integration of two proven technologies: switching and routing. In fact, Layer 3 switches are running the same routing routines and protocols as traditional routers. The main difference between traditional routing and Layer 3 switching is the addition of a group of Layer 2 switching domains and the execution of routing routines for most packets via an ASIC ­ in hardware instead of software. Where a traditional router would have one, or at best a few, Fast Ethernet ports, the DGS-3308 Layer 3 switch has eight Gigabit Ethernet ports, including two which are GBIC-based. Where a traditional router would have one or two high-speed serial WAN connections, the DGS-3308 relies upon Gigabit Ethernet ports to connect to a separate device, which in turn, connects the network to a WAN or the Internet. The DGS-3308 can be thought of as Fast Ethernet Layer 2 switching domains with a wire-speed router between each domain. It can be deployed in a network between a traditional router and the intranetwork. The traditional router and its associated WAN interface would then handle routing between the intranetwork and the WAN (the Internet, for example) while the Layer 3 switch would handle routing within the LAN (between the Fast Ethernet Layer 2 domains). Any installed Layer 2 switches, and indeed the entire subnetting scheme, would remain in place. The DGS-3308FG can also replace key traditional routers for data centers and server farms, routing between these locations and the rest of the network, and providing eight ports of Layer 2 switching performance combined with wire-speed routing. Backbone routers can also be replaced with DGS-3208FG and DGS-3208TG switches and a series of DGS-3308 switches could be linked via the Gigabit Ethernet ports. Routers that service WAN connections would remain in place, but would now be removed from the backbone and connected to the DGS-3308 via a Gigabit Ethernet port. The backbone itself could be migrated to Gigabit Ethernet, or faster technologies as they become available. Policy services can then be introduced (or enhanced) in the backbone infrastructure and maintained throughout the network ­ even to the desktop. With a distributed infrastructure and a logical management structure, network performance becomes easier to measure and fine-tune. With the completion of the migration of the backbone to Gigabit or higher-performance technologies, the result is inherently scalable and easily evolved for future technologies. This core network will also become the termination point for Virtual Private Networks (VPNs) for remote office access to the enterprise infrastructure. The DGS-3308 can then be thought of as accomplishing two objectives. First as a tool to provide high-performance access to enterprise data servers and infrastructure, and second, to enhance the performance of network equipment already 2 8-port Gigabit Ethernet Switch User's Guide installed. Many network segments display poor performance, but the Ethernet wire is only carrying a fraction of its total traffic capacity. The problem is not the network, but the ability of the connected devices to utilize the full capacity of the network. The DGS-3308 can eliminate network bottlenecks to high-traffic areas, and improve the utilization of the network's installed bandwidth. The Functions of a Layer 3 Switch Traditional routers, once the core components of large networks, became an obstacle to the migration toward nextgeneration networks. Attempts to make software-based routers forward packets more quickly were inadequate. A layer 3 switch does everything to a packet that a traditional router does: · · · · · · Determines forwarding path based on Layer 3 information Validates the integrity of the Layer 3 header via checksum Verifies packet expiration and updates accordingly Processes and responds to any optional information Updates forwarding statistics in the Management Information Base Applies security controls A Layer 3 switch can be placed anywhere within a network core or backbone, easily and cost-effectively replacing the traditional collapsed backbone router. The DGS-3308 Layer 3 switch communicates with a WAN router using a standard Gigabit Ethernet or GBIC-based port. Multiple DGS-3308 switches can be linked via the Gigabit Ethernet ports. Features The DGS-3308 was designed for easy installation and high performance in an environment where traffic on the network and the number of users increase continuously. Switch features include: Ports · · · · · · · · Six 1000BASE-SX (SC-type fiber transceiver) for the DGS-3308FG or six 1000BASE-T (10/100/1000M Fast/Gigabit Ethernet) for the DGS-3308TG. Two GBIC-based Gigabit Ethernet ports. Fully compliant with IEEE 802.3z. Fully compliant with IEEE 802.3 10BASE-T, IEEE 802.3u 100BASE-TX, and IEEE 802.3ab 1000BASE-T (DGS3308TG only). Support Full Duplex operations. Supports auto-negotiation for 10M/100M/1000M speed (DGS-3308TG only). IEEE 802.3x compliant Flow Control support for full duplex. Supports Head of Line Blocking. 3 8-port Gigabit Ethernet Switch User's Guide · · Per device packet buffer: 512Kbytes. RS-232 DCE Diagnostic port (console port) for setting up and managing the Switch via a connection to a console terminal or PC using a terminal emulation program. Performance Features Layer 2 Switching Features · · · · · · · · · · · 16 Gbps switching fabric capacity Wire speed packet forwarding rate per system. Store and forward switching scheme. Support 8K MAC address. Support Broadcast Storm control function. Support Port Mirroring. Port Trunking support for Gigabit Ethernet ports. 802.1D Spanning Tree support. 802.1Q Tagged VLAN support, including GVRP (GARP VLAN Registration Protocol) support for automatic VLAN configuration distribution. 802.1p priority support (4 priority queues). Support IGMP Snooping. Layer 3 Switching Features · · · · · · · · · · · Wire speed IP forwarding. Hardware-based Layer 3 IP switching. IP packet forwarding rate up to 12 Mpps. 2K active IP address entry table per device. Supports RIP ­ (Routing Information Protocol) versions I and II. Support OSPF routing protocol. Supports IP version 4. IGMP version 1 and 2 support (RFC 1112 and RFC 2236). Supports PIM Dense Mode (draft-ietf-pim-v2-dm-03.txt). Supports DVMRP (draft-ietf-idmr-dvmrp-v3-09.txt). Supports IP multi-netting. 4 8-port Gigabit Ethernet Switch User's Guide · · · Supports IP packet de-fragmentation. Supports Path MTU discovery. Supports 802.1D frame support. Traffic Classification and Prioritization · · · Based on 802.1p priority bits. Based on MAC address. 4 priority queues. Management · · · · · · · RS-232 console port for out-of-band network management and system diagnosis via a console terminal or PC. Spanning Tree Algorithm Protocol for creation of alternative backup paths and prevention of network loops. SNMP v.1 Agent. Telnet remote control console. In-band control and configuration via SNMP based software. Flash memory for software upgrades. This can be done in-band via TFTP. Built-in SNMP management: § § § § § § § § § § § § § · · RFC 1213 MIB II. RFC 1493 Bridge MIB. RFC 1757 Four groups of RMON: Statistics, History, Alarm, and Event. RFC 1724 RIP v2 MIB. RFC 2737 Entity MIB. RFC 2674 P-Bridge MIB. RFC 2233 IF MIB. RFC 2096 IP Forward MIB. RFC 1907 SNMPv2 MIB IGMP IGMP-STD MIB. PIM MIB. This was extracted from draft-ief-idmr-pim-mib-03.txt. DVMRP MIB. This was extracted from draft-thaler-dvmrp-mib-04.txt. IPMROUTE MIB. This was extracted from draft-ietf-idmr-multicast-routmib-05.txt. Supports Web-based management. TFTP support. 5 8-port Gigabit Ethernet Switch User's Guide · · · · · BOOTP support. IP filtering on the management interface. DHCP Client support. DHCP Relay Agent. Password enabled. Optional Redundant Power Supply The DGS-3308 supports the optional DPS-1000 (Redundant Power Supply) to provide automatic power supply monitoring and switchover to a redundant power supply (located in the chassis of the DPS-1000) in case of a failure in the Switch's internal power supply. Fast Ethernet Technology 100Mbps Fast Ethernet (or 100BASE-T) is a standard specified by the IEEE 802.3 LAN committee. It is an extension of the 10Mbps Ethernet standard with the ability to transmit and receive data at 100Mbps, while maintaining the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Ethernet protocol. Gigabit Ethernet Technology Gigabit Ethernet is an extension of IEEE 802.3 Ethernet utilizing the same packet structure, format, and support for CSMA/CD protocol, full duplex, flow control, and management objects, but with a tenfold increase in theoretical throughput over 100Mbps Fast Ethernet and a one hundred-fold increase over 10Mbps Ethernet. Since it is compatible with all 10Mbps and 100Mbps Ethernet environments, Gigabit Ethernet provides a straightforward upgrade without wasting a company's existing investment in hardware, software, and trained personnel. Gigabit Ethernet enables fast optical fiber connections and Unshielded Twisted Pair connections to support video conferencing, complex imaging, and similar data-intensive applications. Likewise, since data transfers occur 10 times faster than Fast Ethernet, servers outfitted with Gigabit Ethernet NIC's are able to perform 10 times the number of operations in the same amount of time. 6 8-port Gigabit Ethernet Switch User's Guide 2 UNPACKING AND SETUP This chapter provides unpacking and setup information for the Switch. Unpacking Open the shipping carton of the Switch and carefully unpack its contents. The carton should contain the following items: · · · · · · One DGS-3308TG or DGS-3308FG 8-port Gigabit Ethernet Layer 3 Switch Mounting kit: 2 mounting brackets and screws Four rubber feet with adhesive backing One AC power cord One Installation Guide This User's Guide on CD-ROM with Registration Card If any item is found missing or damaged, please contact your local D-Link reseller for replacement. Installation Use the following guidelines when choosing a place to install the Switch: · · · · The surface must support at least 3 kg. The power outlet should be within 1.82 meters (6 feet) of the device. Visually inspect the power cord and see that it is secured to the AC power connector. Make sure that there is proper heat dissipation from and adequate ventilation around the switch. Do not place heavy objects on the switch. Desktop or Shelf Installation When installing the Switch on a desktop or shelf, the rubber feet included with the device should first be attached. Attach these cushioning feet on the bottom at each corner of the device. Allow adequate space for ventilation between the device and the objects around it. 7 8-port Gigabit Ethernet Switch User's Guide Figure 2-1. Installing rubber feet for desktop installation Rack Installation The DGS-3308 can be mounted in an EIA standard-sized, 19-inch rack, which can be placed in a wiring closet with other equipment. To install, attach the mounting brackets on the Switch's side panels (one on each side) and secure them with the screws provided. Figure 2- 2A. Attaching the mounting brackets to the Switch Then, use the screws provided with the equipment rack to mount the switch on the rack. 8 8-port Gigabit Ethernet Switch User's Guide Figure 2-2B. Installing the Switch on an equipment rack Power on The DGS-3308 can be used with AC power supply 100 - 240 VAC, 50 - 60 Hz. The Switch's power supply will adjust to the local power source automatically and may be powered on without having any or all LAN segment cables connected. After the Switch is plugged in, the LED indicators should respond as follows: · · · All LED indicators will momentarily blink. This blinking of the LED indicators represents a reset of the system. The Power LED indicator will blink while the Switch loads onboard software and performs a self-test. After approximately 20 seconds, the LED will light again to indicate the switch is in a ready state. The Console LED indicator will remain ON if there is a connection at the RS-232 port, otherwise this LED indicator is OFF. Power Failure As a precaution in the event of a power failure, unplug the switch. When power is resumed, plug the Switch back in. 9 8-port Gigabit Ethernet Switch User's Guide 3 IDENTIFYING EXTERNAL COMPONENTS This chapter describes the front panel, rear panel, and LED indicators of the DGS-3308. Front Panel The front panel of the Switch consists of LED indicators, an RS-232 communication port, two GBIC-based Gigabit Ethernet ports, and either six 1000BASE-SX ports (DGS-3308FG) or six 1000BASE-T ports (DGS-3308-TG). Figure 3-1a. Front panel view of the DGS-3308FG Figure 3-1b. Front panel view of the DGS-3308TG · · · · Comprehensive LED indicators display the status of the Switch and the network (see the LED Indicators section below). An RS-232 DCE console port for setting up and managing the switch via a connection to a console terminal or PC using a terminal emulation program. Six Gigabit Ethernet ports (1000BASE-SX for DGS-3308FG and 1000BASE-T for DGS-3308TG). Two GBIC-based Gigabit Ethernet ports. Rear Panel The rear panel of the switch consists of a slot for the optional DPS-1000 (Redundant Power Supply) and an AC power connector. Figure 3-2. Rear panel view of the Switch 10 8-port Gigabit Ethernet Switch User's Guide · The AC power connector is a standard three-pronged connector that supports the power cord. Plug-in the female connector of the provided power cord into this socket, and the male side of the cord into a power outlet. Supported input voltages range from 100 ~ 240 VAC at 50 ~ 60 Hz. Side Panels The right side panel of the Switch contains two system fans (see the top part of the diagram below). The left side panel contains heat vents. Figure 3-3. Side panel views of the Switch · The system fans are used to dissipate heat. The sides of the system also provide heat vents to serve the same purpose. Do not block these openings, and leave at least 6 inches of space at the rear and sides of the switch for proper ventilation. Be reminded that without proper heat dissipation and air circulation, system components might overheat, which could lead to system failure. LED Indicators The LED indicators of the Switch include Power, Console, Link/Act, and RPS In Use. The following shows the LED indicators for the Switch along with an explanation of each indicator. · · · Power ­ This indicator on the front panel should be lit during the Power-On Self Test (POST). It will light green approximately 2 seconds after the Switch is powered on to indicate the ready state of the device. Console ­ This indicator is lit green when the Switch is being managed via out-of-band/local console management through the RS-232 console port using a straight-through serial cable. Link/Act ­ These indicators are located to the left and right of each port. They are lit when there is a secure connection (or link) to a device at any of the ports. The LEDs blink whenever there is reception or transmission (i.e. Activity--Act) of data occurring at a port. RPS in Use ­ This indicator is lit when the optional DPS-1000 Redundant Power Supply is being used. · 11 8-port Gigabit Ethernet Switch User's Guide 4 CONNECTING THE SWITCH This chapter describes how to connect the DGS-3308FG/DGS-3308TG to your Gigabit Ethernet network. PC to Switch A PC can be connected to the Switch via a four-pair Category 5 cable or a fiber optic cable. The PC should be connected to any of the eight ports of the DGS-3308FG/DGS-3308TG. Figure 4-1. Switch connected to a PC or Workstation The LED indicators for PC connection are dependent on the LAN card capabilities. If LED indicators are not illuminated after making a proper connection, check the PC's LAN card, the cable, Switch conditions, and connections. The following LED indicator state is possible for a PC to Switch connection: · The Link/Act LED indicator lights up upon hooking up a PC that is powered on. Switch to Switch (other devices) The Switch can be connected to another switch or other devices (routers, bridges, etc.) via a fiber optic cable. 12 8-port Gigabit Ethernet Switch User's Guide Figure 4-2. Switch to switch connection 13 8-port Gigabit Ethernet Switch User's Guide 5 SWITCH MANAGEMENT AND OPERATING CONCEPTS This chapter discusses many of the concepts and features used to manage the switch, as well as the concepts necessary for the user to understand the functioning of the Switch. Further, this chapter explains many important points regarding these features. Configuring the Switch to implement these concepts and make use of its many features is discussed in detail in the next chapters. Some concepts are presented that are not currently implemented on the Switch. They are included to give a user who is unfamiliar with the concepts a brief overview of IP routing that is more complete ­ aid in the incorporation of the DGS3308 in existing IP routed networks. Local Console Management A local console is a terminal or a workstation running a terminal emulation program that is connected directly to the switch via the RS-232 console port on the front of the switch. A console connection is referred to as an `Out-of-Band' connection, meaning that console is connected to the switch using a different circuit than that used for normal network communications. So, the console can be used to set up and manage the switch even if the network is down. Local console management uses the terminal connection to operate the console program built-in to the Switch (see Chapter 6, "Using the Console Interface"). A network administrator can manage, control and monitor the switch from the console program. The DGS-3308 contains a CPU, memory for data storage, flash memory for configuration data, operational programs, and SNMP agent firmware. These components allow the Switch to be actively managed and monitored from either the console port or the network itself (out-of-band, or in-band). Diagnostic (console) port (RS-232 DCE) Out-of-band management requires connecting a terminal, such as a VT-100 or a PC running a terminal emulation program (such as HyperTerminal, which is automatically installed with Microsoft Windows) a to the RS-232 DCE console port of the Switch. Switch management using the RS-232 DCE console port is called Local Console Management to differentiate it from management performed via management platforms, such as D-View, HP OpenView, etc. Web-based Management describes management of the Switch performed over the network (in-band) using the switch's built-in Web-based management program (see Chapter 7, "Web-based Network Management"). The operations to be performed and the facilities provided by these two built-in programs are identical. The console port is set at the factory for the following configuration: · Baud rate: 9,600 14 8-port Gigabit Ethernet Switch User's Guide · · · · Data width: Parity: Stop bits: Flow Control 8 bits none 1 None Make sure the terminal or PC you are using to make this connection is configured to match these settings. If you are having problems making this connection on a PC, make sure the emulation is set to VT-100. If you still don't see anything, try hitting + r to refresh the screen. IP Addresses and SNMP Community Names Each Switch must be assigned its own IP Address, which is used for communication with an SNMP network manager or other TCP/IP application (for example BOOTP, TFTP). The Switch's default IP address is 10.90.90.90. You can change the default Switch IP Address to meet the specification of your networking address scheme. The Switch is also assigned a unique MAC address by the factory. This MAC address cannot be changed, and can be found from the initial boot console screen ­ shown below. Figure 5-1. Boot screen The Switch's MAC address can also be found from the console program under the Switch Information menu item, as shown below. 15 8-port Gigabit Ethernet Switch User's Guide Figure 5-2. Switch Information screen In addition, you can also set an IP Address for a gateway router. This becomes necessary when the network management station is located on a different IP network from the Switch, making it necessary for management packets to go through a router to reach the network manager, and vice-versa. For security, you can set in the Switch a list of IP Addresses of the network managers that you allow to manage the Switch. You can also change the default SNMP Community Strings in the Switch and set the access rights of these Community Strings. In addition, a VLAN may be designated as a Management VLAN. Traps Note: Traps are messages that alert you of events that occur on the Switch. The events can be as serious as a reboot (someone accidentally turned OFF the Switch), or less serious like a port status change. The Switch generates traps and sends them to the network manager (trap recipient). Trap recipients are special users of the network who are given certain rights and access in overseeing the maintenance of the network. Trap recipients will receive traps sent from the Switch; they must immediately take certain actions to avoid future failure or breakdown of the network. You can also specify which network managers may receive traps from the Switch by entering a list of the IP addresses of authorized network managers. Up to four trap recipient IP addresses, and four corresponding SNMP community strings can be entered. Note: SNMP community strings function like passwords in that the community string entered for a given IP address must be used in the management station software, or a trap will be sent. The following are trap types the Switch can send to a trap recipient: 16 8-port Gigabit Ethernet Switch User's Guide · Cold Start ­ This trap signifies that the Switch has been powered up and initialized such that software settings are reconfigured and hardware systems are rebooted. A cold start is different from a factory reset in that configuration settings saved to non-volatile RAM used to reconfigure the switch. Warm Start ­ This trap signifies that the Switch has been rebooted, however the POST (Power On Self-Test) is skipped. Authentication Failure ­ This trap signifies that someone has tried to logon to the switch using an invalid SNMP community string. The Switch automatically stores the source IP address of the unauthorized user. New Root ­ This trap indicates that the Switch has become the new root of the Spanning Tree, the trap is sent by the switch soon after its election as the new root. This implies that upon expiration of the Topology Change Timer the new root trap is sent out immediately after the Switch's election as the new root. Topology Change (STP) ­ A Topology Change trap is sent by the Switch when any of its configured ports transitions from the Learning state to the Forwarding state, or from the Forwarding state to the Blocking state. The trap is not sent if a new root trap is sent for the same transition. New Root (STP) ­ A New Root trap is sent be the switch whenever a new root port is elected within an STP group. Link Up ­ This trap is sent whenever the link of a port changes from link down to link up. Link Down ­ This trap is sent whenever the link of a port changes from link up to link down. · · · · · · · MIBs Management and counter information are stored in the Switch in the Management Information Base (MIB). The Switch uses the standard MIB-II Management Information Base module. Consequently, values for MIB objects can be retrieved from any SNMP-based network management software. In addition to the standard MIB-II, the Switch also supports its own proprietary enterprise MIB as an extended Management Information Base. These MIBs may also be retrieved by specifying the MIB's Object-Identity (OID) at the network manager. MIB values can be either read-only or read-write. Read-only MIBs variables can be either constants that are programmed into the Switch, or variables that change while the Switch is in operation. Examples of read-only constants are the number of port and type of ports. Examples of read-only variables are the statistics counters such as the number of errors that have occurred, or how many kilobytes of data have been received and forwarded through a port. Read-write MIBs are variables usually related to user-customized configurations. Examples of these are the Switch's IP Address, Spanning Tree Algorithm parameters, and port status. If you use a third-party vendors' SNMP software to manage the Switch, a diskette listing the Switch's propriety enterprise MIBs can be obtained by request. If your software provides functions to browse or modify MIBs, you can also get the MIB values and change them (if the MIBs' attributes permit the write operation). This process however can be quite involved, since you must know the MIB OIDs and retrieve them one by one. SNMP Simple Network Management Protocol (SNMP) is an OSI layer 7 (the application layer) protocol for remotely monitoring and configuring network devices. SNMP enables network management stations to read and modify the settings of gateways, routers, switches, and other network devices. SNMP can be used to perform many of the same functions as a directly connected console, or can be used within an integrated network management software package such as DView. The Switch has a software program called an `agent' that processes SNMP requests, but the user program that makes the requests and collects the responses runs on a management station (a designated computer on the network). The SNMP agent and the user program both use the UDP/IP protocol to exchange packets. 17 8-port Gigabit Ethernet Switch User's Guide Authentication The authentication protocol ensures that both the router SNMP agent and the remote user SNMP application program discard packets from unauthorized users. Authentication is accomplished using `community strings', which function like passwords. The remote user SNMP application and the router SNMP must use the same community string. SNMP community strings of up to 20 characters may be entered under the Remote Management Setup menu of the console program. Packet Forwarding The Switch enters the relationship between destination MAC or IP addresses and the Ethernet port or gateway router the destination resides on into its forwarding table. This information is then used to forward packets. This reduces the traffic congestion on the network, because packets, instead of being transmitted to all ports, are transmitted to the destination port only. Example: if Port 1 receives a packet destined for a station on Port 2, the Switch transmits that packet through Port 2 only, and transmits nothing through the other ports. This process is referred to as `learning' the network topology. MAC Address Aging Time The Aging Time affects the learning process of the Switch. Dynamic forwarding table entries, which are made up of the source and destination MAC addresses and their associated port numbers, are deleted from the table if they are not accessed within the aging time. The aging time can be from 10 to 1,000,000 seconds with a default value of 300 seconds. A very long aging time can result in dynamic forwarding table entries that are out-of-date or no longer exist. This may cause incorrect packet forwarding decisions by the Switch. If the Aging Time is too short however, many entries may be aged out too soon. This will result in a high percentage of received packets whose source addresses cannot be found in the forwarding table, in which case the switch will broadcast the packet to all ports, negating many of the benefits of having a switch. Static forwarding entries are not affected by the aging time. Filtering The Switch uses a filtering database to segment the network and control communication between segments. It can also filter packets off the network for intrusion control. Static filtering entries can be made by MAC Address or IP Address filtering. Each port on the Switch is a unique collision domain and the switch filters (discards) packets whose destination lies on the same port as where it originated. his keeps local packets from disrupting communications on other parts of the network. For intrusion control, whenever a switch encounters a packet originating from or destined to a MAC address or an IP Address entered into the filter table, the switch will discard the packet. Some filtering is done automatically by the switch: · · · Dynamic filtering ­ automatic learning and aging of MAC addresses and their location on the network. Filtering occurs to keep local traffic confined to its segment. Filtering done by the Spanning Tree Protocol, which can filter packets based on topology, making sure that signal loops don't occur. Filtering done for VLAN integrity. Packets from a member of a VLAN (VLAN 2, for example) destined for a device on another VLAN (VLAN 3) will be filtered. 18 8-port Gigabit Ethernet Switch User's Guide Some filtering requires the manual entry of information into a filtering table: · MAC address filtering ­ the manual entry of specific MAC addresses to be filtered from the network. Packets sent from one manually entered MAC address can be filtered from the network. The entry may be specified as either a source, a destination, or both. IP address filtering ­ the manual entry of specific IP addresses to be filtered from the network (switch must be in IP Routing mode). Packets sent from one manually entered IP address to another can be filtered from the network. The entry may specified as either a source, a destination, or both (switch must be in IP Routing mode). · IP Addressing and Subnetting This section gives basic information needed to configure your Layer 3 switch for IP routing. The information includes how IP addresses are broken down and how subnetting works. You will learn how to assign each interface on the router an IP address with a unique subnet. Definitions · · · · · · · IP Address ­ the unique number ID assigned to each host or interface on a network. IP addresses have the form xxx.xxx.xxx.xxx. Subnet ­ a portion of a network sharing a particular network address. Subnet mask ­ a 32-bit number used to describe which portion of a Network Address refers to the subnet and which portion refers to the host. Subnet masks have the form xxx.xxx.xxx.xxx. Interface ­ a network connection IP Interface ­ another name for subnet. Network Address ­ the resulting 32-bit number from a bitwise logical AND operation performed between an IP address and a subnet mask. Subnet Address ­ another name for network address. Note: In a subnetted network, all addresses consist of two parts: an IP address and a subnet mask. The two are used together and one is meaningless without the other. IP Addresses The Internet Protocol (IP) was designed for routing data between network sites. Later, it was adapted for routing between networks (referred to as "subnets") within a site. The IP defines a way of generating an unique number that can be assigned each network in the internet and each of the computers on each of those networks. This number is called the IP address. IP addresses use a "dotted decimal" notation. Here are some examples of IP addresses written in this format: 1. 2. 3. 210.202.204.205 189.21.241.56 125.87.0.1 This allows IP address to be written in a string of 4 decimal (base 10) numbers. Computers can only understand binary (base 2) numbers, and these binary numbers are usually grouped together in bytes, or eight bits. (A bit is a binary digit ­ either a "1" or a "0"). The dots (periods) simply make the IP address easier to read. A computer sees an IP address not as four decimal numbers, but as a long string of binary digits (32 binary digits or 32 bits, IP addresses are 32-bit addresses). The three IP addresses in the example above, written in binary form are: 1. 2. 3. 11010010.11001010.11001100.11001101 10111101.00010101.11110001.00111000 01111101.01010111.00000000.00000001 The dots are included to make the numbers easier to read. 19 8-port Gigabit Ethernet Switch User's Guide Eight binary bits are called a `byte' or an `octet'. An octet can represent any decimal value between `0' (00000000) and `255' (11111111). IP addresses, represented in decimal form, are four numbers whose value is between `0' to `255'. The total range of IP addresses are then: Lowest possible IP address Highest possible IP address 0.0.0.0 255.255.255.255 To convert decimal numbers to 8-bit binary numbers (and vice-versa), you can use the following chart: Binary Octet Digit Decimal Equivalent Binary Number 128+64+32+16+8+4+2+1= 255 27 128 1 26 64 1 25 32 1 24 16 1 23 8 1 22 4 1 21 2 1 2 0 1 1 Table 5-1. Binary to Decimal Conversion Each digit in an 8-bit binary number (an octet) represents a power of two. The left-most digit represents 2 raised to the 7th power (2x2x2x2x2x2x2=128) while the right-most digit represents 2 raised to the 0th power (any number raised to the 0th power is equal to one, by definition). IP addresses actually consist of two parts, one identifying the network and one identifying the destination (node) within the network. The IP address discussed above is one part and a second number called the Subnet mask is the other part. To make this a bit more confusing, the subnet mask has the same numerical form as and IP address. Address Classes Address classes refer to the range of numbers in the subnet mask. Grouping the subnet masks into classes makes the task of dividing a network into subnets a bit easier. There are 5 address classes. The first 4 bits in the IP address determine which class the IP address falls in. · · · · · Class A addresses begin with 0xxx, or 1 to 126 decimal. Class B addresses begin with 10xx, or 128 to 191 decimal. Class C addresses begin with 110x, or 192 to 223 decimal. Class D addresses begin with 1110, or 224 to 239 decimal. Class E addresses begin with 1111, or 240 to 254 decimal. Addresses beginning with 01111111, or 127 decimal, are reserved. They are used for internal testing on a local machine (called loopback). The address 127.0.0.1 can always be pinged from a local node because it forms a loopback and points back to the same node. Class D addresses are reserved for multicasting. Class E Addresses are reserved for future use. They are not used for node addresses. The part of the IP address that belongs to the network is the part that is `hidden' by the `1's in the subnet mask. This can be seen below: · · · Class A Class B Class C NETWORK.node.node.node NETWORK.NETWORK.node.node NETWORK.NETWORK.NETWORK.node For example, the IP address 10.42.73.210 is a Class A address, so the Network part of the address (called the Network Address) is the first octet (10.x.x.x). The node part of the address is the last three octets (x.42.73.210). To specify the network address for a given IP address, the node part is set to all "0"s. In our example, 10.0.0.0 specifies the network address for 10.42.73.210. When the node part is set to all "1"s, the address specifies a broadcast address. So, 10.255.255.255 is the broadcast address for the network 10.0.0.0. 20 8-port Gigabit Ethernet Switch User's Guide Subnet Masking A subnet mask can be applied to an IP address to identify the network and the node parts of the address. A bitwise logical AND operation between the IP address and the subnet mask results in the Network Address. For example: 00001010.00101010.01001001.11010010 10.42.73.210 11111111.00000000.00000000.00000000 255.0.0.0 Class A IP address Class A Subnet Mask 00001010.00000000.00000000.00000000 10.0.0.0 Network Address The Default subnet masks are: · · · Class A ­ 11111111.00000000.00000000.00000000 Class B ­ 11111111.11111111.00000000.00000000 Class C ­ 1111111.11111111.11111111.00000000 255.0.0.0 255.255.0.0 255.255.255.0 Additional bits can be added to the default subnet mask for a given Class to further subnet a network. When a bitwise logical AND operation is performed between the subnet mask and the IP address, the result defines the Subnet Address. Some restrictions apply to subnet addresses. Addresses of all "0"s and all "1"s are reserved for the local network (when a host does not know its network address) and for all hosts on the network (the broadcast address). This also applies to subnets. A subnet address cannot be all "0"s or all "1"s. A 1-bit subnet mask is also not allowed. Calculating the Number of Subnets and Nodes To calculate the number of subnets and nodes, use the formula (2n ­ 2) where n = the number of bits in either the subnet mask or the node portion of the IP address. Multiplying the number of subnets by the number of nodes available per subnet gives the total number of nodes for the entire network. Example 00001010.00101010.01001001.11010010 11111111.11100000.00000000.00000000 00001010.00100000.00000000.00000000 00001010.00101010.11111111.11111111 10.42.73.210 255.224.0.0 10.32.0.0 10.32.255.255 Class A IP address Subnet Mask Network Address Broadcast Address This example uses an 11-bit subnet mask. (There are 3 additional bits added to the default Class A subnet mask). So the number of subnets is: 23 ­ 2 = 8 ­ 2 = 6 Subnets of all "0"s and all "1"s are not allowed, so 2 subnets are subtracted from the total. The number of bits used in the node part of the address is 24 ­ 3 = 21 bits, so the total number of nodes is: 221 ­ 2 = 2,097,152 ­ 2 = 2,097,150 Multiplying the number of subnets times the number of nodes gives 12,582,900 possible nodes. Note that this is less than the 16,777,214 possible nodes that an unsubnetted class A network would have. Subnetting reduces the number of possible nodes for a given network, but increases the segmentation of the network. 21 8-port Gigabit Ethernet Switch User's Guide Classless InterDomain Routing ­ CIDR Under CIDR, the subnet mask notation is reduced to a simplified shorthand. Instead of specifying all of the bits of the subnet mask, it is simply listed as the number of contiguous "1"s (bits) in the network portion of the address. Look at the subnet mask of the above example in binary - 11111111.11100000.00000000.00000000 ­ and you can see that there are 11 "1"s or 11 bits used to mask the network address from the node address. Written in CIDR notation this becomes: 10.32.0.0/11 # of Bit s 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Subnet Mask CID R Not atio n /10 /11 /12 /13 /14 /15 /16 /17 /18 /19 /20 /21 /22 /23 /24 /25 /26 /27 /28 /29 /30 # of Subnets # of Hosts Total Hosts 255.192.0.0 255.224.0.0 255.240.0.0 255.248.0.0 255.252.0.0 255.254.0.0 255.255.0.0 255.255.128.0 255.255.192.0 255.255.224.0 255.255.240.0 255.255.248.0 255.255.252.0 255.255.254.0 255.255.255.0 255.255.255.128 255.255.255.192 255.255.255.224 255.255.255.240 255.255.255.248 255.255.255.252 2 6 14 30 62 126 254 510 1022 2046 4094 8190 16382 32766 65534 131070 262142 525286 1048574 2097150 4194302 4194302 2097150 1048574 524286 262142 131070 65534 32766 16382 8190 4094 2046 1022 510 254 126 62 30 14 6 2 8388604 12582900 14680036 15728580 16252804 16514820 16645636 16710660 16742404 16756740 16760836 16756740 16742404 16710660 16645636 16514820 16252804 15728580 14680036 12582900 8388604 Table 5-2. Class A Subnet Masks # of Bits 2 3 4 5 6 7 8 9 10 11 12 13 14 Subnet Mask CIDR Notatio n /18 /19 /20 /21 /22 /23 /24 /25 /26 /27 /28 /29 /30 # of Subnets 2 6 14 30 62 126 254 510 1022 2046 4094 8190 16382 # of Hosts 16382 8190 4094 2046 1022 510 254 126 62 30 14 6 2 Total Hosts 32764 49140 57316 61380 63364 64260 64516 64260 63364 61380 57316 49140 32764 255.255.192 255.255.224.0 255.255.240.0 255.255.248.0 255.255.252.0 255.255.254.0 255.255.255.0 255.255.255.12 8 255.255.255.19 2 255.255.255.22 4 255.255.255.24 0 255.255.255.24 8 255.255.255.25 22 8-port Gigabit Ethernet Switch User's Guide 2 Table 5-3. Class B Subnet Masks # of Bits 2 3 4 5 6 Subnet Mask 255.255.255.192 255.255.255.224 255.255.255.240 255.255.255.248 255.255.255.252 CIDR Notation /26 /27 /28 /29 /30 # of Subnets 2 6 14 30 62 # of Hosts 62 30 14 6 2 Total Hosts 124 180 196 180 124 Table 5-4. Class C Subnet Masks 802.1Q VLANs A VLAN is a collection of end nodes grouped by logic instead of physical location. End nodes that frequently communicate with each other are assigned to the same VLAN, regardless of where they are physically on the network. Logically, a VLAN can be equated to a broadcast domain, because broadcast packets are forwarded to only members of the VLAN on which the broadcast was initiated. Notes About VLANs 1. N o matter what basis is used to uniquely identify end nodes and assign these nodes VLAN membership, packets cannot cross VLANs without a network device performing a routing function between the VLANs. The DGS-3308 supports only IEEE 802.1Q VLANs. The port untagging function can be used to remove the 802.1 tag from packet headers to maintain compatibility with devices that are tagunaware. The Switch's default - in both Layer 2 Only mode and IP Routing mode - is to assign all ports to a single 802.1Q VLAN named DEFAULT_VLAN. As new VLANs are created, the member ports assigned to the new VLAN will be removed from the DEFAULT_ VLAN port member list. The DEFAULT_VLAN has a VID = 1. An IP interface called System in the IP interface entry menu also has a VID = 1, and therefore corresponds to the DEFAULT_VLAN. There is no difference in the creation, deletion, configuration, or editing of 802.1Q VLANs whether the Switch is in Layer 2 Only, or IP Routing mode. There is a difference in the behavior of VLANs when the Switch is in Layer 2 Only or IP Routing mode. In Layer 2 Only mode, network resources cannot be shared across VLANs. In IP Routing mode, network resources are shared via routing. The Switch allows the assignment of an IP interface to each VLAN, in IP Routing mode. The VLANs must be configured before setting up the IP interfaces. In addition, an IP addressing scheme must be determined. Some consideration is required to arrive at a suitable combination of VLANs and IP interfaces. See the section titled IP Addressing and Subnetting in Chapter 5 for more information. 2. 3. 4. 5. 6. A VLAN that is not assigned an IP interface will behave as a layer 2 VLAN ­ and IP routing will not be possible on this VLAN regardless of the Switch's operating mode. IEEE 802.1Q VLANs Some relevant terms: · Tagging ­ The act of putting 802.1Q VLAN information into the header of a packet. 23 8-port Gigabit Ethernet Switch User's Guide · · · Untagging ­ The act of stripping 802.1Q VLAN information out of the packet header. Ingress port ­ A port on a switch where packets are flowing into the switch and VLAN decisions must be made. Egress port ­ A port on a switch where packets are flowing out of the switch, either to another switch or to an end station, and tagging decisions must be made. IEEE 802.1Q (tagged) VLANs are implemented on the Switch. 802.1Q VLANs require tagging, which enables them to span the entire network (assuming all switches on the network are IEEE 802.1Q-compliant). IEEE 802.1Q VLANs also allow for dynamic VLAN registration using GVRP. VLANs can also provide a level of security to your network. IEEE 802.1Q VLANs will only deliver packets between stations that are members of the VLAN. Any port can be configured as either tagging or untagging. The untagging feature of IEEE 802.1Q VLANs allow VLANs to work with legacy switches that don't recognize VLAN tags in packet headers. The tagging feature allows VLANs to span multiple 802.1Q-compliant switches through a single physical connection and allows Spanning Tree to be enabled on all ports and work normally. The IEEE 802.1Q standard restricts the forwarding of untagged packets to the VLAN the receiving port is a member of. The main characteristics of IEEE 802.1Q are as follows: · · · Assigns packets to VLANs by filtering. Assumes the presence of a single global spanning tree. Uses an explicit tagging scheme with one-level tagging. 802.1Q VLAN Packet Forwarding Packet forwarding decisions are made based upon the following three types of rules: · · · Ingress rules ­ rules relevant to the classification of received frames belonging to a VLAN. Forwarding rules between ports ­ decides filter or forward the packet Egress rules ­ determines if the packet must be sent tagged or untagged. 24 8-port Gigabit Ethernet Switch User's Guide Figure 5-3. IEEE 802.1Q Packet Forwarding 802.1Q VLAN Tags The figure below shows the 802.1Q VLAN tag. There are four additional octets inserted after the source MAC address. Their presence is indicated by a value of 0x8100 in the EtherType field. When a packet's EtherType field is equal to 0x8100, the packet carries the IEEE 802.1Q/802.1p tag. The tag is contained in the following two octets and consists of 3 bits or user priority, 1 bit of Canonical Format Identifier (CFI ­ used for encapsulating Token Ring packets so they can be carried across Ethernet backbones) and 12 bits of VLAN ID (VID). The 3 bits of user priority are used by 802.1p. The VID is the VLAN identifier and is used by the 802.1Q standard. The tag is inserted into the packet header making the entire packet longer by 4 octets. All of the information contained in the packet originally is retained. Figure 5-4. IEEE 802.1Q Tag 25 8-port Gigabit Ethernet Switch User's Guide The EtherType and VLAN ID are inserted after the MAC source address, but before the originial EtherType/Length or Logical Link Control. Because the packet is now a bit longer than it was originally, the Cyclic Redundancy Check (CRC) must be recalculated. Figure 5-5. Adding an IEEE 802.1Q Tag Port VLAN ID Packets that are tagged (are carrying the 802.1Q VID information) can be transmitted from one 802.1Q compliant network device to another with the VLAN information intact. This allows 802.1Q VLANs to span network devices (and indeed, the entire network ­ if all network devices are 802.1Q compliant). Every physical port on a switch has a PVID. 802.1Q ports are also assigned a PVID, for use within the switch. If no VLANs are defined on the switch, all ports are then assigned to a default VLAN with a PVID equal to 1. Untagged packets are assigned the PVID of the port on which they were received. Forwarding decisions are based upon this PVID, in so far as VLANs are concerned. Tagged packets are forwarded according to the VID contained within the tag. Tagged packets are also assigned a PVID, but the PVID is not used to make packet forwarding decisions, the VID is. Tag-aware switches must keep a table to relate PVIDs within the switch to VIDs on the network. The switch will compare the VID of a packet to be transmitted to the VID of the port that is to transmit the packet. If the two VIDs are different, the switch will drop the packet. Because of the existence of the PVID for untagged packets and the VID for tagged packets, tag-aware and tag-unaware network devices can coexist on the same network. A switch port can have only one PVID, but can have as many VIDs as the switch has memory in its VLAN table to store them. Because some devices on a network may be tag-unaware, a decision must be made at each port on a tag-aware device before packets are transmitted ­ should the packet to be transmitted have a tag or not? If the transmitting port is connected to a tag-unaware device, the packet should be untagged. If the transmitting port is connected to a tag-aware device, the packet should be tagged. Tagging and Untagging Every port on an 802.1Q compliant switch can be configured as tagging or untagging. Ports with tagging enabled will put the VID number, priority and other VLAN information into the header of all packets that flow into and out of it. If a packet has previously been tagged, the port will not alter the packet, thus keeping the VLAN information intact. The VLAN information in the tag can then be used by other 802.1Q compliant devices on the network to make packet forwarding decisions. Ports with untagging enabled will strip the 802.1Q tag from all packets that flow into and out of those ports. If the packet doesn't have an 802.1Q VLAN tag, the port will not alter the packet. Thus, all packets received by and forwarded by an untagging port will have no 802.1Q VLAN information. (Remember that the PVID is only used internally within the switch). Untagging is used to send packets from an 802.1Q-compliant network device to a non-compliant network device. 26 8-port Gigabit Ethernet Switch User's Guide Ingress Filtering A port on a switch where packets are flowing into the switch and VLAN decisions must be made is referred to as an ingress port. If ingress filtering is enabled for a port, the switch will examine the VLAN information in the packet header (if present) and decide whether or not to forward the packet. If the packet is tagged with VLAN information, the ingress port will first determine if the ingress port itself is a member of the tagged VLAN. If it is not, the packet will be dropped. If the ingress port is a member of the 802.1Q VLAN, the switch then determines if the destination port is a member of the 802.1Q VLAN. If it is not, the packet is dropped. If the destination port is a member of the 802.1Q VLAN, the packet is forwarded and the destination port transmits it to its attached network segment. If the packet is not tagged with VLAN information, the ingress port will tag the packet with its own PVID as a VID (if the port is a tagging port). The switch then determines if the destination port is a member of the same VLAN (has the same VID) as the ingress port. If it does not, the packet is dropped. If it has the same VID, the packet is forwarded and the destination port transmits it on its attached network segment. This process is referred to as ingress filtering and is used to conserve bandwidth within the switch by dropping packets that are not on the same VLAN as the ingress port at the point of reception. This eliminates the subsequent processing of packets that will just be dropped by the destination port. Layer 3-Based VLANs The DGS-3308 allows an IP subnet to be configured for each 802.1Q VLAN that exists on the switch. Even though a switch inspects a packet's IP address to determine VLAN membership, no route calculation is performed, the RIP or OSPF protocols are not employed, and packets traversing the switch are bridged using the Spanning Tree algorithm. A switch that implements layer 3 (or `subnet') VLANs without performing any routing function between these VLANs is referred to as performing `IP Switching'. IP switching does not allow packets to cross VLANs (in this case ­ IP subnets) without a network device performing a routing function between the VLANs (IP subnets). The DGS-3308 does not directly support IP switching, however it is possible to do the equivalent by assigning IP subnets to configured VLANs and then disabling the Routing Information Protocol (RIP). This will prevent packets from crossing IP subnets without going through an external router. VLANs in Layer 2 Only Mode The switch initially configures one VLAN, VID = 1, called the DEFAULT_VLAN. The factory default setting assigns all ports on the switch to the DEFAULT_VLAN. As new VLANs are configured, there respective member ports are removed from the DEFAULT_VLAN. If the DEFAULT_VLAN is reconfigured, all ports are again assigned to it. Ports that are not desired to be part of the DEFAULT_VLAN are removed during the configuration. Packets cannot cross VLANs if the switch is in Layer 2 Only mode.If a member of one VLAN wants to connect to another VLAN, the link must be through an external router. When the switch is in Layer 2 Only mode, 802.1Q VLANs are supported. Setting up IP Interfaces The Layer 3 switch allows ranges of IP addresses (OSI layer 3) to be assigned to VLANs (OSI layer 2). Each VLAN must be configured prior to setting up the corresponding IP interface. An IP addressing scheme must then be established, and implemented when the IP interfaces are set up on the switch. 27 8-port Gigabit Ethernet Switch User's Guide An example is presented below: VLAN Name System (default) Engineering Marketing Shipping VID 1 2 3 4 Switch Ports 7, 8 1, 2 5, 6 3,4 Table 5-5. VLAN Example ­ Assigned Ports In this case, 4 IP interfaces are required, so a CIDR notation of 10.32.0.0/10 (or a 10-bit) addressing scheme will work. This addressing scheme will give a subnet mask of 11111111.11000000.00000000.00000000 (binary) or 255.192.0.0 (decimal). Using a 10.xxx.xxx.xxx IP address notation, the above example would give 4 network addresses and 4 subnets. Any IP address from the allowed range of IP addresses for each subnet can be chosen as an IP address for an IP interface on the switch. For this example, we have chosen the next IP address above the network address: VLAN Name System (default) Engineering Marketing Shipping VID 1 2 3 4 Network Address 10.0.0.0 10.64.0.0 10.128.0.0 10.192.0.0 IP Address 10.0.0.1 10.64.0.1 10.128.0.1 10.192.0.1 Table 5-6. VLAN Example ­ Assigned IP Addresses The 4 IP interfaces, each with an IP address (listed in the table above), and a subnet mask of 255.192.0.0 can be entered into the Setup IP Interface menu. Spanning Tree Protocol The IEEE 802.1D Spanning Tree Protocol allows for the blocking of links between switches that form loops within the network. When multiple links between switches are detected, a primary link is established. Duplicated links are blocked from use and become standby links. The protocol allows for the duplicate links to be used in the event of a failure of the primary link. Once the Spanning Tree Protocol is configured and enabled, primary links are established and duplicated links are blocked automatically. The reactivation of the blocked links (at the time of a primary link failure) is also accomplished automatically ­ without operator intervention. This automatic network reconfiguration provides maximum uptime to network users. However, the concepts of the Spanning Tree Algorithm and protocol are a complicated and complex subject and must be fully researched and understood. It is possible to cause serious degradation of the performance of the network if the Spanning Tree is incorrectly configured. Please read the following before making any changes from the default values. The DGS-3308 STP allows two levels of spanning trees to be configured. The first level constructs a spanning tree on the links between switches. This is referred to as the Switch or Global level. The second level is on a port group basis. Groups of ports are configured as being members of a spanning tree and the algorithm and protocol are applied to the group of ports. This is referred to as the Port or VLAN level. 28 8-port Gigabit Ethernet Switch User's Guide The Switch STP performs the following functions: · · · · Creates a single spanning tree from any combination of switching or bridging elements. Creates multiple spanning trees ­ from any combination of ports contained within a single switch, in userspecified groups. Automatically reconfigures the spanning tree to compensate for the failure, addition, or removal of any element in the tree. Reconfigures the spanning tree without operator intervention. STP Operation Levels The Switch allows for two levels of operation: the switch level and the port level. The switch level forms a spanning tree consisting of links between one or more switches. The port level constructs a spanning tree consisting of groups of one or more ports. The STP operates in much the same way for both levels. Note: On the switch level, STP calculates the Bridge Identifier for each switch and then sets the Root Bridge and the Designated Bridges. Note: On the port level, STP sets the Root Port and the Designated Ports. The following are the user-configurable STP parameters for the switch level: Parameter Bridge Identifier (Not userconfigurable except by setting priority below) Priority Description A combination of the User-set priority and the switch's MAC address. The Bridge Identifier consists of two parts: a 16-bit priority and a 48-bit Ethernet MAC address A relative priority for each switch ­ lower numbers give 29 Default Value 32768 + MAC 32768 8-port Gigabit Ethernet Switch User's Guide switch ­ lower numbers give a higher priority and a greater chance of a given switch being elected as the root bridge Hello Time The length of time between broadcasts of the hello message by the switch Measures the age of a received BPDU for a port and ensures that the BPDU is discarded when its age exceeds the value of the maximum age timer. The amount time spent by a port in the learning and listening states waiting for a BPDU that may return the port to the blocking state. 2 seconds Maximum Age Timer 20 seconds Forward Timer Delay 15 seconds Table 5-7. STP Parameters ­ Switch Level The following are the user-configurable STP parameters for the port or port group level: Variable Port Priority Description A relative priority for each port ­ lower numbers give a higher priority and a greater chance of a given port being elected as the root port A value used by STP to evaluate paths ­ STP calculates path costs and selects the path with the minimum cost as the active path. Default Value 32768 Port Cost 19 ­ 100Mbps Fast Ethernet ports 4 ­ 1000Mbps Gigabit Ethernet ports Table 5-8. STP Parameters ­ Port Group Level Bridge Protocol Data Units For STP to arrive at a stable network topology, the following information is used: · · · The unique switch identifier The path cost to the root associated with each switch port The port identifier STP communicates between switches on the network using Bridge Protocol Data Units (BPDUs). Each BPDU contains the following information: · The unique identifier of the switch that the transmitting switch currently believes is the root switch 30 8-port Gigabit Ethernet Switch User's Guide · · The path cost to the root from the transmitting port The port identifier of the transmitting port The switch sends BPDUs to communicate and construct the spanning-tree topology. All switches connected to the LAN on which the packet is transmitted will receive the BPDU. BPDUs are not directly forwarded by the switch, but the receiving switch uses the information in the frame to calculate a BPDU, and, if the topology changes, initiates a BPDU transmission. The communication between switches via BPDUs results in the following: · · · · · One switch is elected as the root switch The shortest distance to the root switch is calculated for each switch A designated switch is selected. This is the switch closest to the root switch through which packets will be forwarded to the root. A port for each switch is selected. This is the port providing the best path from the switch to the root switch. Ports included in the STP are selected. Creating a Stable STP Topology to make the fastest link the root port. If all switches have STP enabled with default settings, the switch with the lowest MAC address in the network will become the root switch. By increasing the priority (lowering the priority number) of the best switch, STP can be forced to select the best switch as the root switch. When STP is enabled using the default parameters, the path between source and destination stations in a switched network might not be ideal. For instance, connecting higher-speed links to a port that has a higher number than the current root port can cause a root-port change. STP Port States The BPDUs take some time to pass through a network. This propagation delay can result in topology changes where a port that transitioned directly from a Blocking state to a Forwarding state could create temporary data loops. Ports must wait for new network topology information to propagate throughout the network before starting to forward packets. They must also wait for the packet lifetime to expire for BPDU packets that were forwarded based on the old topology. The forward delay timer is used to allow the network topology to stabilize after a topology change. In addition, STP specifies a series of states a port must transition through to further ensure that a stable network topology is created after a topology change. Each port on a switch using STP exists is in one of the following five states: · · · · · Blocking ­ the port is blocked from forwarding or receiving packets Listening ­ the port is waiting to receive BPDU packets that may tell the port to go back to the blocking state Learning ­ the port is adding addresses to its forwarding database, but not yet forwarding packets Forwarding ­ the port is forwarding packets Disabled ­ the port only responds to network management messages and must return to the blocking state first A port transitions from one state to another as follows: · · From initialization (switch boot) to blocking From blocking to listening or to disabled 31 8-port Gigabit Ethernet Switch User's Guide · · · · From listening to learning or to disabled From learning to forwarding or to disabled From forwarding to disabled From disabled to blocking Figure 5-6. STP Port State Transitions You can modify each port state by using management software. When you enable STP, every port on every switch in the network goes through the blocking state and then transitions through the states of listening and learning at power up. If properly configured, each port stabilizes to the forwarding or blocking state. No packets (except BPDUs) are forwarded from, or received by, STP enabled ports until the forwarding state is enabled for that port. Default Spanning-Tree Configuration Feature Enable state Port priority Port cost Bridge Priority Default Value STP enabled for all ports 128 19 32,768 Table 5-9. Default STP Parameters 32 8-port Gigabit Ethernet Switch User's Guide User-Changeable STA Parameters The factory default setting should cover the majority of installations. However, it is advisable to keep the default settings as set at the factory; unless, it is absolutely necessary. The user changeable parameters in the Switch are as follows: · · Priority ­ A Priority for the switch can be set from 0 to 65535. 0 is equal to the highest Priority. Hello Time ­ The Hello Time can be from 1 to 10 seconds. This is the interval between two transmissions of BPDU packets sent by the Root Bridge to tell all other Switches that it is indeed the Root Bridge. If you set a Hello Time for your Switch, and it is not the Root Bridge, the set Hello Time will be used if and when your Switch becomes the Root Bridge. Note: The Hello Time cannot be longer than the Max. Age. Otherwise, a configuration error will occur. · Max. Age ­ The Max. Age can be from 6 to 40 seconds. At the end of the Max. Age, if a BPDU has still not been received from the Root Bridge, your Switch will start sending its own BPDU to all other Switches for permission to become the Root Bridge. If it turns out that your Switch has the lowest Bridge Identifier, it will become the Root Bridge. Forward Delay Timer ­ The Forward Delay can be from 4 to 30 seconds. This is the time any port on the Switch spends in the listening state while moving from the blocking state to the forwarding state. Note: Observe the following formulas when setting the above parameters: Max. Age Max. Age · · 2 x (Forward Delay - 1 second) 2 x (Hello Time + 1 second) · Port Priority ­ A Port Priority can be from 0 to 255. The lower the number, the greater the probability the port will be chosen as the Root Port. Port Cost ­ A Port Cost can be set from 1 to 65535. The lower the number, the greater the probability the port will be chosen to forward packets. Illustration of STP A simple illustration of three switches connected in a loop is depicted in Figure 5-7. In this example, you can anticipate some major network problems if the STP assistance is not applied. If switch A broadcasts a packet to switch B, switch B will broadcast it to switch C, and switch C will broadcast it to back to switch A ... and so on. The broadcast packet will be passed indefinitely in a loop, potentially causing a network failure. In this example, STP breaks the loop by blocking the connection between switch B and C. The decision to block a particular connection is based on the STP calculation of the most current Bridge and Port settings. Now, if switch A broadcasts a packet to switch C, then switch C will drop the packet at port 2 and the broadcast will end there. Setting-up STP using values other than the defaults, can be complex. Therefore, you are advised to keep the default factory settings and STP will automatically assign root bridges/ports and block loop connections. Influencing STP to choose a particular switch as the root bridge using the Priority setting, or influencing STP to choose a particular port to block using the Port Priority and Port Cost settings is, however, relatively straight forward. 33 8-port Gigabit Ethernet Switch User's Guide Figure 5-7. Before Applying the STA Rules In this example, only the default STP values are used. Figure 5-8. After Applying the STA Rules The switch with the lowest Bridge ID (switch C) was elected the root bridge, and the ports were selected to give a high port cost between switches B and C. The two (optional) Gigabit ports (default port cost = 4) on switch A are connected to one (optional) Gigabit port on both switch B and C. The redundant link between switch B and C is deliberately chosen as a 100 Mbps Fast Ethernet link (default port cost = 19). Gigabit ports could be used, but the port cost should be increased from the default to ensure that the link between switch B and switch C is the blocked link. Internet Protocols This is a brief introduction to TCP/IP, or the collection of Internet protocols that are commonly called TCP/IP. It is intended to give the reader some understanding of the terminology and the resources available. It is not intended to be a complete description. 34 8-port Gigabit Ethernet Switch User's Guide Protocol Layering The task of connecting users to networks, and then networks to networks, is made somewhat easier by dividing up the overall job into simpler, but related, tasks. Each task is structured to be resilient to failures in the connecting hardware, software, data loss, data corruption, and data received out of order. Taken together, these tasks are referred to as a protocol suite. Each task, or protocol, must communicate with other protocols. To manage this communication, the concept of layering was introduced as a way of structuring the overall network. The idea of protocol layering is to start with the most basic layer, the physical (or hardware) layer, and to define data formats and functions for that layer. The physical layer passes data to next higher layer, the data link layer, and so on until one user is connected to another. Protocol layering then provides clearly defined breaks in the process of communicating over a network. Each break in the process has a clearly defined data format so that the layer below can perform its task in any way that is suitable, so long as the data it generates is in the format expected by the next layer. The advantage of this approach is that the exact method and tools (or software and hardware) used to accomplish the task at each layer is not critically important. Hardware and software designers are free to improve the performance or to reduce the cost of accomplishing the task of each protocol layer, so long as the data format between layers conforms to the defined formats (and of course, the layer's task is accomplished). The protocol layer concept currently used by the Internet, the OSI seven-layer model, was developed from earlier, simpler layered models. Much of the current layer model owes its origin to the Xerox Network Systems (XNS) model. The OSI (Open Systems Interconnection) model actually refers to a system of protocols proposed by ISO (the International Standards Organization) that are themselves not widely used or supported. The layered model itself is, however, taken as the framework for nearly all modern networking. A diagram of the OSI model is shown below (note that this is not a complete listing of the protocols contained within each layer of the model): Figure 5-8. OSI Seven Layer Network Model Each layer has a distinct set of tasks to accomplish and clearly defined formats in which to receive and forward data and messages. A distinct set of programs, executing a distinct set of protocols, is required to accomplish the task set by each layer. Although the layers are separated from other layers in the model, they must all communicate and interoperate. For this to work, there must be very well-defined and well-known methods for transferring messages and data. Within a device connected to a network, this inter-layer communication is managed by the device's protocol stack. 35 8-port Gigabit Ethernet Switch User's Guide Using the protocol layering model to visualize the organization of the network software, Layer 2 represents switching and Layer 3 represents routing. In fact, the protocol layering model gives only guidelines for writing programs to accomplish certain tasks and functions. How the layers communicate within a protocol stack (for example, within a network device or a computer) is determined by the operating system programmers. So long as the communication between devices on the network follows the well-defined and well-known methods and data formats, the protocol stack can accomplish its tasks in any way suitable. Figure 5-9. The Protocol Stack Elements on the same layer of a protocol stack are known as peers. They communicate with other peers, in other protocol stacks (on other network devices) using the well-defined and well-known methods and formats. Messages and data are transferred via published (and therefore well-known) protocols. Elements within the same stack communicate using an internal interface. This interface is part of the operating system and is usually not published (and therefore not well-known). In addition, internal protocol stack interfaces are generally proprietary. This means that communication within the protocol stack has the same characteristics as a protocol in that two protocol stacks from the same operating system vendor will communicate (within the stack) in the same way. The difference from a protocol is that stacks from different operating system vendors (or two different operating system products from the same vendor) may communicate within the stack in completely different ways. The result is that communication between layers in within a protocol stack (and within a given network device) are often proprietary and different from communication within a second protocol stack. Communication between peers (between two protocol stacks, but at the same layer) is accomplished by well-known and published protocols. So, peers communicate in an open and consistent way, and peers from completely different systems from different vendors can communicate easily. This principle has allowed the rapid growth of layered networking. A brief description of the most commonly used layers of the OSI model is helpful to understand the scope of how protocol layering works. 36 8-port Gigabit Ethernet Switch User's Guide Layer 1 Layer 2 This is commonly called the switching layer. It allows for the addressing of end stations and for the interconnection of end stations. This allows a practical way to construct simple but high-performance networks connecting thousands of end stations. Switching forwards packets based on the unique Media Access Control (MAC) address of each end station. Switches records the MAC address and the port number of end stations and enter the information into a lookup table. In this way, a switch `learns' the location of end stations and other switches attached to its ports. Switching is usually limited to the Local Area Network (LAN) and requires a routing function to connect to the Internet or to a Wide Area Network (WAN). Layer 3 This is commonly called the routing layer. The backbone of the Internet, along with the backbones of the networks of many large organizations, is built on a layer 3 foundation. The Internet Protocol (IP) is the most important layer 3 protocol. In addition to layer 2 MAC addresses, each IP packet contains source and destination IP addresses. IP itself is not a very complex protocol. The IP suite of protocols do, however, provide an extensive range of functions. Some examples are: the Dynamic Host Configuration Protocol (DHCP) which can assign IP configurations to network devices, the Domain Name System (DNS) which manages the association of IP addresses with text names, the Routing Information Protocol (RIP) which enables layer 3 network devices to direct data to destinations in other networks. IP also allows for transmitting packets from a single point to multiple destinations (known as IP multicasting). Layer 4 This is commonly called the transport layer. It is responsible for the communication path between user applications and the network. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) are the most well-known layer 4 protocols. TCP is a `connection-oriented' protocol. It requires a connection to be established before data is exchanged. UDP is a `connection-less' protocol. It requires on connection to be setup before it transmits data. Because UDP does not have the overhead of establishing a connection before transmitting data, it is frequently used for multicast transmissions. TCP and UDP also have very different error recovery mechanisms. Both TCP and UDP are layered on top of IP, but IP has very limited error recovery or detection. TCP keeps track of the transmitted data and retransmits lost or corrupted data. UDP relies upon the application (at a higher layer) to keep track of transmitted data. Layer 7 This commonly called the application layer. It provides access to application software running either on a computer or other network device. Application software usually does not communicate directly with the transport layer, but uses other software from a communication library, such as the WinSock library. The application software designers must decide on the type of transport protocol that is most suitable for their task. Databases, for example, require error-free transmission, so TCP would be the best choice. Multimedia is much less sensitive to errors, so the low overhead of UDP becomes the best choice. 37 8-port Gigabit Ethernet Switch User's Guide TCP/IP Transmission Control Protocol/Internet Protocol (TCP/IP) is the official name of a suite of protocols designed to allow computers to communicate and share resources across a network. TCP and IP are only the two best known protocols of the suite, but TCP/IP is used to refer to the entire suite. TCP/IP is itself a layered set of protocols. For two computers to communicate across a network, there is first a protocol that defines a set of commands used by the two computers to identify the sender, the recipient, and the content of the message. The application then relies on TCP/IP to actually transmit and receive the packets that make up the message. TCP keeps track of what was sent and received, and retransmits any lost or corrupted packets. If the message is too large for a single packet, TCP divides the message into as many packets as are necessary. TCP also makes sure these packets are receive and reassembled in the correct order. IP routes the packets generated by TCP from their source to their destinations. This may require the packets to cross other networks. IP can route packets through networks connected with gateways so that a user on one network can communicate with any user on any connected network. IP is not aware of the relationship between individual packets, or the contents of the packet ­ except for the source and destination IP addresses. This is called demultiplexing. The information required by IP is contained in a series of headers which are added to or removed from the packet as it travels from network to network. A header is a few octets of data added to the beginning of a packet to keep track of it. As more data is required for the packet to cross a network, a new header is added. When the data is no longer required, the header is removed and the data in the previous header is used to forward the packet. This process is called encapsulation. To send a packet over the internet, many levels of encapsulation may be used, and IP does all of this transparently to the user. TCP and UDP Well-Known Ports Network devices and computers connected to a network can have multiple connections with other devices and computers simultaneously. Received packets must be directed to the appropriate application at the receiving end. TCP and UDP use IP addresses to keep track of which devices are part of the connection, and port numbers to keep track of which applications within each device are communicating. To retrieve a file from a server using the File Transfer Protocol (FTP), a connection from the user, at 10.0.0.1 (for example) to an FTP Server, at 10.0.0.2 (for example). TCP then opens a connection on the user's computer using some random port number, 1234. The connection on the FTP server is opened using the well-known port number 21 for the FTP application. So, FTP is running on 10.0.0.1 port number 1234, and FTP Server is running on 10.0.0.1 port number 21 (the well-known port for FTP). There is a published list of well-known ports (sometimes called sockets) for many applications. There is no need for a well-known port to be chosen for 10.0.0.1. It is only necessary for TCP to know which port has been chosen. The FTP Server, on the other hand, must have a well-known port number so that connections can be made, commands sent, and messages exchanged. Note that the connection is actually described by a set of four numbers, the IP address and the TCP port number for the local end and the IP address and the TCP port number for the remote end. The Internet address is in the IP header and the TCP port number is in the TCP header. No two connections can have the same set of numbers, but only one number of the four must be different. This allows two different users to send files to the same destination, at the same time. Two FTP Server Connections TCP ports Internet addresses 38 8-port Gigabit Ethernet Switch User's Guide Connection 1 1234, 21 10.42.73.23 210.128.12.1 Connection 2 1235, 21 10.42.73.23 210.128.12.1 So the local computer, 10.42.73.23 has two connections to the FTP Server, 210.128.12.1. Commands sent from 10.42.73.23 are received by the FTP Server on the well-known TCP port number 21, but the transmitted files are received by 10.42.73.23 on either TCP port number 1234 or 1235, depending on which port issued the command. FTP actually uses two different connections. One for sending commands and a second one opened when a request to send data is issued. This is done to allow the user to continue sending commands (such as, abort the file transfer). Connections with a remote terminal use a single connection. When a command is to be sent, a special character is sent that indicates the next character is part of a command. UDP and ICMP TCP will divide large messages into several packets and manage the sending and receiving of all of these packets. Many applications do not require messages that must be divided into many smaller packets. The User Datagram Protocol (UDP) is designed for applications that do not need sequences of packets to be put together. UDP also does not keep track of what is sent and cannot resend data. UDP does use port numbers in much the same way as TCP. UDP allows several programs to make connections to a server at the same time. UDP port numbers are used just like TCP port numbers and there are well-known port numbers for servers that use UDP. Figure 5-10. UDP Packet Header Note that a UDP header is shorter than a TCP header, but it still has source and destination port numbers, and a checksum. The Internet Control Message Protocol (ICMP) is alternative protocol. It is used for messages intended for the TCP/IP software itself, such as error messages, rather than by any particular user program. ICMP can also be used for find information about the network. There are no port numbers since ICMP messages are processed by the network software itself. Packet Headers TCP TCP takes messages and data that are too long to fit into a single packet and divides the transmission up among a series of packets, transmits them, and reassembles them in the correct order when they are received. To do this, TCP needs to know how large a packet the network can handle. The TCPs at either end of a connection tell each other how large a packet they can process. The smaller of the two sizes is selected. 39 8-port Gigabit Ethernet Switch User's Guide The TCP header is added to the beginning of each packet. This header contains at least 20 octets including the source and destination TCP port numbers. Each packet is given a sequence number that is used to ensure that the packets are received in the correct order. The packets themselves are not numbered, instead, the octets the packet contains is numbered. So if there are 100 octets of data in each packet, the first packet would be numbered 0, the second 100, the third 200, and so on. A checksum is calculated by adding up all the octets in the packet and the result is put in the header. The receiving TCP calculates its own checksum and if the two checksums differ, the packet is dropped. Figure 5-11. TCP Packet Header An acknowledgement is sent to indicate that the packets have been received. This is simply a packet with its acknowledgement number field filled in. The acknowledgement number is the number of octets of data received at the time the acknowledgement packet is sent. If the sender does not receive an acknowledgement within a reasonable amount of time, the data is resent. The window field controls the amount of data in transit at any one time. Each end of a connection indicates how much data it is currently able to receive by putting that number of octets in the window field. As the computer receives data, the number in the window field is decremented and when it reaches zero, the sender must stops transmitting. As the recipient processes data, it increases its window, indicating that it is ready to receive more data. IP TCP sends packets to IP, along with source and destination IP addresses. IP is not concerned with the contents of the packets or with the TCP header. IP routes the packet from the source to the destination. IP adds its own header to the packet to allow intermediate gateways or other network devices to forward the packet. The header contains the source and destination IP addresses, a protocol number, and a checksum. The protocol number allows IP to pass the packet to the appropriate protocol (usually TCP) at the receiving end. The checksum is calculated in same way as the TCP checksum and allows IP to verify that the data was not corrupted in transit. 40