Cisco Systems 78-11741-02 BGP Synchronization Examples, BGP Path Filtering by Neighbor Examples

Configuring BGP

BGP Configuration Examples

BGP Synchronization Examples

The example shown in Figure 59 shows how to use the no synchronization router configuration command. In the figure, synchronization is on, and Router B does not advertise network 198.92.68.0 to Router A until an IGRP route for network 198.92.68.0 exists. If you specify the no synchronization router configuration command, Router B advertises network 198.92.68.0 as soon as possible. However, because routing information still must be sent to interior peers, you must configure a full iBGP mesh.

Figure 59 BGP Synchronization Configuration

	AS
Router	IGRP

Router A Router B Router

Router

IBGP connections

Physical connectivity

EGBP connections

Router

Network 198.92.68.0

S2566

BGP Path Filtering by Neighbor Examples

The following example shows BGP path filtering by neighbor. Only the routes that pass autonomous system path access list 2 will be sent to 193.1.12.10. Similarly, only routes passing access list 3 will be accepted from 193.1.12.10.

router bgp	200
neighbor 193.1.12.10 remote-as			100
neighbor 193.1.12.10 filter-list 1				out
neighbor 193.1.12.10 filter-list 2				in
ip as-path	access-list 1 permit		_109_
ip as-path	access-list 2 permit		_200$
ip as-path	access-list 2	permit	^100$
ip as-path	access-list 3	deny _690$
ip as-path	access-list 3	permit	.*

Cisco IOS IP Configuration Guide

IPC-340