Cisco Systems 78-11741-02 Configuring BGP Interactions with IGPs, IPC-302, Timer Starts Wakeups

Configuring BGP

Configuring Basic BGP Features

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Local host: 172.16.232.178, Local port: 179

Foreign host: 172.16.232.179, Foreign port: 11002

Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)

Event Timers (current time is 0x2CF49CF8):
Timer	Starts	Wakeups	Next
Retrans	12518	0	0x0
TimeWait	0	0	0x0
AckHold	12514	12281	0x0
SendWnd	0	0	0x0
KeepAlive	0	0	0x0
GiveUp	0	0	0x0
PmtuAger	0	0	0x0
DeadWait	0	0	0x0

iss:	273358651	snduna:	273596614	sndnxt: 273596614		sndwnd:	15434
irs:	190480283	rcvnxt:	190718186	rcvwnd:	15491	delrcvwnd:	893
SRTT:	300 ms, RTTO: 607 ms, RTV: 3 ms, KRTT:				0 ms

minRTT: 0 ms, maxRTT: 300 ms, ACK hold: 200 ms

Flags: passive open, nagle, gen tcbs

Datagrams (max data segment is 1460 bytes):

Rcvd: 24889 (out of order: 0), with data: 12515, total data bytes: 237921

Sent: 24963 (retransmit: 0), with data: 12518, total data bytes: 237981

Configuring BGP Interactions with IGPs

If your autonomous system will be passing traffic through it from another autonomous system to a third autonomous system, make sure that your autonomous system is consistent about the routes that it advertises. For example, if your BGP were to advertise a route before all routers in your network had learned about the route through your IGP, your autonomous system could receive traffic that some routers cannot yet route. To prevent this condition from occurring, BGP must wait until the IGP has propagated routing information across your autonomous system, thus causing BGP to be synchronized with the IGP. Synchronization is enabled by default.

In some cases, you need not synchronize. If you will not be passing traffic from a different autonomous system through your autonomous system, or if all routers in your autonomous system will be running BGP, you can disable synchronization. Disabling this feature can allow you to carry fewer routes in your IGP and allow BGP to converge more quickly. To disable synchronization, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# no synchronization	Disables synchronization between BGP and an IGP.

See the “BGP Path Filtering by Neighbor Examples” section at the end of this chapter for an example of BGP synchronization.

In general, you will not want to redistribute most BGP routes into your IGP. A common design is to redistribute one or two routes and to make them exterior routes in IGRP, or have your BGP speaker generate a default route for your autonomous system. When redistributing from BGP into IGP, only the routes learned using eBGP get redistributed.

Cisco IOS IP Configuration Guide

IPC-302