Catalyst 3550 Multilayer Switch Software Configuration Guide, 12.1(12c)EA1
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This guide is for the networking professional managing the Catalyst 3550 switch, hereafter referred to as the switch or the multilayer switch. Before using this guide, you should have experience working with the Cisco IOS and be familiar with the concepts and terminology of Ethernet and local area networking.


This guide provides the information you need to configure Layer 2 and Layer 3 software features on your switch. The Catalyst 3550 switch is supported by either the standard multilayer software image (SMI), which provides Layer 2+ features and basic Layer 3 routing, or the enhanced multilayer software image (EMI), which provides Layer 2+ features, full Layer 3 routing, and advanced services. All Catalyst 3550 Gigabit Ethernet switches are shipped with the EMI pre-installed. Catalyst 3550 Fast Ethernet switches are shipped with either the SMI or the EMI pre-installed. After initial deployment, you can order the Enhanced Multilayer Software Image Upgrade kit to upgrade Catalyst 3550 Fast Ethernet switches from the SMI to the EMI.

This guide provides procedures for using the commands that have been created or changed for use with the Catalyst 3550 switch. It does not provide detailed information about these commands. For detailed information about these commands, refer to the Catalyst 3550 Multilayer Switch Command Reference for this release. For information about the standard IOS Release 12.1 commands, refer to the IOS documentation set available from the home page at Service and Support > Technical Documents. On the Cisco Product Documentation home page, select Release 12.1 from the Cisco IOS Software drop-down list.

This guide also includes an overview of the Cluster Management Suite (CMS) web-based, switch management interface, which helps you create and manage clusters of switches. This guide does not provide field-level descriptions of the CMS windows nor does it provide the procedures for configuring switches and switch clusters from CMS. For all CMS window descriptions and procedures, refer to the CMS online help, which is integrated with the software image.

This guide does not describe system messages you might encounter or how to install your switch. For more information, refer to the Catalyst 3550 Multilayer Switch System Message Guide for this release and to the Catalyst 3550 Multilayer Switch Hardware Installation Guide.


This guide is organized into these chapters:

"Overview," lists the software features of this release and provides examples of how the switch can be deployed in a network.

"Using the Command-Line Interface," describes how to access the command modes, use the command-line interface (CLI), and describes CLI messages that you might receive. It also describes how to get help, abbreviate commands, use no and default forms of commands, use command history and editing features, and how to search and filter the output of show and more commands.

"Getting Started with CMS," describes the Cluster Management Suite (CMS) web-based, switch management interface. For information on configuring your web browser and accessing CMS, refer to the release notes. For field-level descriptions of all CMS windows and procedures for using the CMS windows, refer to the online help.

"Assigning the Switch IP Address and Default Gateway," describes how to create the initial switch configuration (for example, assign the switch IP address and default gateway information) by using a variety of automatic and manual methods. It also describes how to modify the switch startup configuration.

"Configuring IE2100 CNS Agents," describes how to configure Cisco Intelligence Engine 2100 (IE2100) Series Cisco Networking Services (CNS) embedded agents on your switch. By using the IE 2100 Series Configuration Registrar network management application, you can automate initial configurations and configuration updates by generating switch-specific configuration changes, sending them to the switch, executing the configuration change, and logging the results.

"Clustering Switches," describes switch clusters and the considerations for creating and maintaining them. The online help provides the CMS procedures for configuring switch clusters. Configuring switch clusters is most easily performed through CMS; therefore, CLI procedures are not provided. Cluster commands are described in the Catalyst 3550 Multilayer Switch Command Reference.

"Administering the Switch," describes how to perform one-time operations to administer your switch. It describes how to set the system date and time, system name and prompt, create a login banner, how to manage the MAC address table, and how to optimize system resources for user-selected features.

"Configuring Switch-Based Authentication," describes how to configure switch-based authentication on your switch. It describes how to prevent unauthorized access to your switch through the use of passwords, privilege levels, the Terminal Access Controller Access Control System Plus (TACACS+), the Remote Authentication Dial-In User Service (RADIUS), Kerberos, and the Secure Shell (SSH).

"Configuring 802.1X Port-Based Authentication," describes how to configure 802.1X port-based authentication to prevent unauthorized devices (clients) from gaining access to the network.

"Configuring Interface Characteristics," defines the types of Layer 2 and Layer 3 interfaces on the switch. It describes the interface command and provides procedures for configuring physical interfaces.

"Configuring VLANs," describes how to create and maintain VLANs. It includes information about the VLAN database, VLAN configuration modes, extended VLANs, VLAN Trunks, and the VLAN Membership Policy Server (VMPS).

"Configuring VTP," describes how to use the VLAN Trunking Protocol (VTP) VLAN database for managing VLANs. It includes VTP characteristics and configuration.

"Configuring Voice VLAN," describes how to configure a voice VLAN on the switch for a connection to an IP phone.

"Configuring 802.1Q and Layer 2 Protocol Tunneling," describes how to use 802.1Q tunneling to maintain and segregate customer VLANs across a service provider infrastructure and Layer 2 protocol tunneling to ensure that all customer sites receive complete STP, CDP, and VTP information.

"Configuring STP," describes how to configure the Spanning Tree Protocol (STP) on your switch.

"Configuring RSTP and MSTP," describes how to configure the Cisco implementation of the IEEE 802.1W Rapid Spanning Tree Protocol (RSTP) and the IEEE 802.1S Multiple STP (MSTP) on your switch. RSTP provides rapid convergence, and MSTP enables VLANs to be grouped into a spanning-tree instance.

"Configuring Optional Spanning-Tree Features," describes how to configure optional spanning-tree features that can be used when your switch is running the per-VLAN spanning-tree (PVST) or the MSTP.

"Configuring the DHCP Option 82 for Subscriber Identification," describes how to configure the Dynamic Host Configuration Protocol (DHCP) relay agent information (option 82) feature so that the switch can include information about itself and the attached client when forwarding DHCP requests from a DHCP client to a DHCP server.

"Configuring IGMP Snooping and MVR," describes how to configure Layer 2 Internet Group Management Protocol (IGMP) snooping. It also describes Multicast VLAN Registration (MVR), a local IGMP snooping feature available on the switch, and how to use IGMP filtering to control multicast group membership.

"Configuring Port-Based Traffic Control," describes how to reduce traffic storms by setting broadcast, multicast, and unicast storm-control threshold levels; how to protect ports from receiving traffic from other ports on a switch; how to block unknown broadcast and unicast traffic; and how to configure port security using secure MAC addresses.

"Configuring CDP," describes how to configure Cisco Discovery Protocol (CDP) on your switch.

"Configuring UDLD," describes how to configure the UniDirectional Link Detection (UDLD) feature. UDLD enables devices connected through fiber-optic or twisted-pair Ethernet cables to monitor the physical configuration of the cables and detect when a unidirectional link exists.

"Configuring SPAN and RSPAN," describes how to configure Switched Port Analyzer (SPAN) and Remote SPAN (RSPAN), which selects network traffic for analysis by a network analyzer such as a SwitchProbe device or other Remote Monitoring (RMON) probe.

"Configuring RMON," describes how to configure remote monitoring (RMON). The RMON feature, which is used with the Simple Network Management Protocol (SNMP) agent in the switch, means that you can monitor all the traffic flowing among switches on all connected LAN segments.

"Configuring System Message Logging," describes how to configure system message logging. It describes the message format, how to change the message display destination device, limit the type of messages sent, configure UNIX server syslog daemon and define the UNIX system logging facility, and timestamp messages.

"Configuring SNMP," describes how to configure the Simple Network Management Protocol (SNMP). It describes how to configure community strings, enable trap managers and traps, set the agent contact and location information, and how to limit TFTP servers used through SNMP.

"Configuring Network Security with ACLs," describes how to configure network security on your switch by creating standard and extended IP access control lists (ACLs) or named MAC extended ACLs and applying them to routed interfaces (router ACLs), Layer 2 interfaces (port ACLs), or VLANs (VLAN maps).

"Configuring QoS," describes how to configure automatic or standard quality of service (QoS) on your switch. With this feature, you can provide preferential treatment to certain types traffic.

"Configuring EtherChannels," describes how to bundle a set of individual ports into a single logical link on Layer 2 and Layer 3 interfaces.

"Configuring IP Unicast Routing," describes how to configuring IP unicast routing on your switch, including configuring IP addressing features, Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF) protocol, Enhanced IGRP (EIGRP), and Border Gateway Protocol (BGP). It includes configuration information and examples for configuring multiple VPN routing/forwarding (multi-VRF) instances in customer edge (CE) devices.

"Configuring HSRP," describes how to use Hot Standby Router Protocol (HSRP) to provide routing redundancy for routing IP traffic without depending on the availability of any single router.

"Configuring Web Cache Services By Using WCCP," describes how to configure your switch to redirect traffic to cache engines (web caches such as the Cisco Cache Engine 550) by using the Web Cache Communication Protocol (WCCP).

"Configuring IP Multicast Routing," how to configuring IP multicast routing. It describes how to use and configure the Internet Group Management Protocol (IGMP), Protocol-Independent Multicast (PIM) protocol, Cisco Group Management Protocol (CGMP) server functionality, and how to inter-operate between PIM and Distance Vector Multicast Routing Protocol (DVMRP) domains.

"Configuring MSDP," describes how to configure the Multicast Source Discovery Protocol (MSDP), which is a mechanism to connect multiple PIM sparse-mode domains.

"Configuring Fallback Bridging," describes how to configure fallback bridging on your switch. With fallback bridging, you can bridge non-IP protocols between VLAN bridge domains and routed ports.

"Troubleshooting," describes how to identify and resolve software problems related to the IOS software. It also described how to identify connectivity problems.

"Supported MIBs," lists the supported MIBs for this release and how to use FTP to access the MIB files.

"Working with the IOS File System, Configuration Files, and Software Images," describes how to manipulate the Flash file system, how to copy configuration files, and how to archive (upload and download) software images.

"Unsupported CLI Commands in Release 12.1(12c)EA1," lists the unsupported command-line interface (CLI) commands that are displayed when you enter the question mark (?) at the switch prompt. The unsupported commands are listed by software feature and command mode.


This publication uses these conventions to convey instructions and information:

Command descriptions use these conventions:

Commands and keywords are in boldface text.

Arguments for which you supply values are in italic.

Square brackets ([ ]) mean optional elements.

Braces ({ }) group required choices, and vertical bars ( | ) separate the alternative elements.

Braces and vertical bars within square brackets ([{ | }]) mean a required choice within an optional element.

Interactive examples use these conventions:

Terminal sessions and system displays are in screen font.

Information you enter is in boldface screen font.

Nonprinting characters, such as passwords or tabs, are in angle brackets (< >).

Notes, cautions, and timesavers use these conventions and symbols:

Note Means reader take note. Notes contain helpful suggestions or references to materials not contained in this manual.

Caution Means reader be careful. In this situation, you might do something that could result equipment damage or loss of data.

Timesaver Means the following will help you solve a problem. The tips information might not be troubleshooting or even an action, but could be useful information.

Related Publications

These documents provide complete information about the switch and are available from this site:

You can order printed copies of documents with a DOC-xxxxxx= number from the sites and from the telephone numbers listed in the "Ordering Documentation" section.

Release Notes for the Catalyst 3550 Multilayer Switch (not orderable but available on

Note Switch requirements and procedures for initial configurations and software upgrades tend to change and therefore appear only in the release notes. Before installing, configuring, or upgrading the switch, refer to the release notes on for the latest information.

Catalyst 3550 Multilayer Switch Software Configuration Guide (order number DOC-7811194=)

Catalyst 3550 Multilayer Switch Command Reference (order number DOC-7811195=)

Catalyst 3550 Multilayer Switch System Message Guide (order number DOC-7811196=)

Cluster Management Suite (CMS) online help (available only from the switch CMS software)

Catalyst 3550 Multilayer Switch Hardware Installation Guide (order number DOC-7811358=)

1000BASE-T Gigabit Interface Converter Installation Note (not orderable but is available on

Catalyst GigaStack Gigabit Interface Converter Hardware Installation Guide (order number DOC-786460=)

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