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Catalyst 3560 Switch Software Configuration Guide
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Chapter 36 Configuring IP Unicast Routing
Steps for Configuring Routing
Static unicast routing forwards packets from predetermined ports through a single path into and out of a
network. Static routing is secure and uses little bandwidth, but does not automatically respond to changes
in the network, such as link failures, and therefore, might result in unreachable destinations. As networks
grow, static routing becomes a labor-intensive liability.
Dynamic routing protocols are used by routers to dynamically calculate the best route for forwarding
traffic. There are two types of dynamic routing protocols:
• Routers using distance-vector protocols maintain routing tables with distance values of networked
resources, and periodically pass these tables to their neighbors. Distance-vector protocols use one
or a series of metrics for calculating the best routes. These protocols are easy to configure and use.
• Routers using link-state protocols maintain a complex database of network topology, based on the
exchange of link-state advertisements (LSAs) between routers. LSAs are triggered by an event in
the network, which speeds up the convergence time or time required to respond to these changes.
Link-state protocols respond quickly to topology changes, but require greater bandwidth and more
resources than distance-vector protocols.
Distance-vector protocols supported by the switch are Routing Information Protocol (RIP), which uses
a single distance metric (cost) to determine the best path and Border Gateway Protocol (BGP), which
adds a path vector mechanism. The switch also supports the Open Shortest Path First (OSPF) link-state
protocol and Enhanced IGRP (EIGRP), which adds some link-state routing features to traditional
Interior Gateway Routing Protocol (IGRP) to improve efficiency.
Note The supported protocols are determined by the software running on the switch. If the switch is running
the IP base image, only default routing, static routing and RIP are supported. All other routing protocols
require the IP services image.
Steps for Configuring Routing
By default, IP routing is disabled on the switch, and you must enable it before routing can take place.
For detailed IP routing configuration information, see the Cisco IOS IP Configuration Guide,
Release 12.2 from the Cisco.com page under Documentation > Cisco IOS Software > 12.2 Mainline
> Configuration Guides.
In the following procedures, the specified interface must be one of these Layer 3 interfaces:
• A routed port: a physical port configured as a Layer 3 port by using the no switchport interface
configuration command.
• A switch virtual interface (SVI): a VLAN interface created by using the interface vlan vlan_id
global configuration command and by default a Layer 3 interface.
• An EtherChannel port channel in Layer 3 mode: a port-channel logical interface created by using
the interface port-channel port-channel-number global configuration command and binding the
Ethernet interface into the channel group. For more information, see the “Configuring Layer 3
EtherChannels” section on page 35-13.
Note The switch does not support tunnel interfaces for unicast routed traffic.
All Layer 3 interfaces on which routing will occur must have IP addresses assigned to them. See the
“Assigning IP Addresses to Network Interfaces” section on page 36-5.