Cabletron Systems 9032578-05 manual Setting the Autonomous System Number, Setting the Router ID

Chapter 12: BGP Configuration Guide

Setting the Autonomous System Number

An autonomous system number identifies your autonomous system to other routers. To set the SSR’s autonomous system number, enter the following command in Configure mode.

Set the SSR’s autonomous system number.

ip-router global set autonomous-system <num1> loops <num2>

The autonomous-system<num1> parameter sets the AS number for the router. Specify a number from 1–65534. The loops <num2> parameter controls the number of times the AS may appear in the as-path. The default is 1.

Setting the Router ID

The router ID uniquely identifies the SSR. To set the router ID to be used by BGP, enter the following command in Configure mode.

Set the SSR’s router ID.

ip-router global set router-id <hostname-or-IPaddr>

If you do not explicitly specify the router ID, then an ID is chosen implicitly by the SSR. A secondary address on the loopback interface (the primary address being 127.0.0.1) is the most preferred candidate for selection as the SSR’s router ID. If there are no secondary addresses on the loopback interface, then the default router ID is set to the address of the first interface that is in the up state that the SSR encounters (except the interface en0, which is the Control Module’s interface). The address of a non point-to-point interface is preferred over the local address of a point-to-point interface. If the router ID is implicitly chosen to be the address of a non-loopback interface, and if that interface were to go down, then the router ID is changed. When the router ID changes, an OSPF router has to flush all its LSAs from the routing domain.

If you explicitly specify a router ID, then it would not change, even if all interfaces were to go down.

Configuring a BGP Peer Group

A BGP peer group is a group of neighbor routers that have the same update policies. To configure a BGP peer group, enter the following command in Configure mode:

Configure a BGP peer group.

bgp create peer-group <number-or-string>type externalinternalrouting [autonomous-system <number>] [proto anyripospfstatic] [interface <interface-name-or-ipaddr>all]

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