Cisco Systems 3560-X, 3750-X Configuring OSPF

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Catalyst 3750-X and 3560-X Switch Software Configuration Guide

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Chapter 42 Configuring IP Unicast Routing Configuring OSPF

Routers connected to broadcast-type IP networks and using distance-vector routing protocols normally

use the split-horizon mechanism to reduce the possibility of routing loops. Split horizon blocks

information about routes from being advertised by a router on any interface from which that information

originated. This feature can optimize communication among multiple routers, especially when links are

broken.

Note In general, we do not recommend disabling split horizon unless you are certain that your application

requires it to properly advertise routes.

Beginning in privileged EXEC mode, follow these steps to disable split horizon on the interface:

To enable the split horizon mechanism, use the ip split-horizon interface configuration command.

Configuring OSPF

This section briefly describes how to configure Open Shortest Path First (OSPF). For a complete

description of the OSPF commands, see the “OSPF Commands” chapter of the Cisco IOS IP Command

Reference, Volume 2 of 3: Routing Protocols, Release 12.2.

Note OSPF classifies different media into broadcast, nonbroadcast, and point-to-point networks. The switch

supports broadcast (Ethernet, Token Ring, and FDDI) and point-to-point networks (Ethernet interfaces

configured as point-to-point links).

OSPF is an Interior Gateway Protocol (IGP) designed expressly for IP networks, supporting IP

subnetting and tagging of externally derived routing information. OSPF also allows packet

authentication and uses IP multicast when sending and receiving packets. The Cisco implementation

supports RFC 1253, OSPF management information base (MIB).

The Cisco implementation conforms to the OSPF Version 2 specifications with these key features:

• Definition of stub areas is supported.

• Routes learned through any IP routing protocol can be redistributed into another IP routing protocol.

At the intradomain level, this means that OSPF can import routes learned through EIGRP and RIP.

OSPF routes can also be exported into RIP.

Command Purpose

Step 1 configure terminal Enter global configuration mode.

Step 2 interface interface-id Enter interface configuration mode, and specify the interface to

configure.

Step 3 ip address ip-address subnet-mask Configure the IP address and IP subnet.

Step 4 no ip split-horizon Disable split horizon on the interface.

Step 5 end Return to privileged EXEC mode.

Step 6 show ip interface interface-id Verify your entries.

Step 7 copy running-config startup-config (Optional) Save your entries in the configuration file.