User's Manual

38-46
Catalyst 3750 Switch Software Configuration Guide
OL-8550-09
Chapter 38 Configuring IP Unicast Routing
Configuring BGP
BGP Version 4 supports classless interdomain routing (CIDR) so you can reduce the size of your routing
tables by creating aggregate routes, resulting in supernets. CIDR eliminates the concept of network
classes within BGP and supports the advertising of IP prefixes.
These sections contain this configuration information:
• Default BGP Configuration, page 38-46
• Enabling BGP Routing, page 38-49
• Managing Routing Policy Changes, page 38-51
• Configuring BGP Decision Attributes, page 38-53
• Configuring BGP Filtering with Route Maps, page 38-55
• Configuring BGP Filtering by Neighbor, page 38-55
• Configuring Prefix Lists for BGP Filtering, page 38-57
• Configuring BGP Community Filtering, page 38-58
• Configuring BGP Neighbors and Peer Groups, page 38-59
• Configuring Aggregate Addresses, page 38-61
• Configuring Routing Domain Confederations, page 38-62
• Configuring BGP Route Reflectors, page 38-62
• Configuring Route Dampening, page 38-63
• Monitoring and Maintaining BGP, page 38-64
For detailed descriptions of BGP configuration, see the “Configuring BGP” chapter in the “IP Routing
Protocols” part of the Cisco IOS IP Configuration Guide, Release 12.2. For details about specific
commands, see the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.2.
Locate these documents from the Cisco.com page under Documentation > Cisco IOS Software > 12.2
Mainline > Configuration Guides or Command References.
For a list of BGP commands that are visible but not supported by the switch, see Appendix D,
“Unsupported Commands in Cisco IOS Release 12.2(55)SE.”
Default BGP Configuration
Table 38-9 shows the basic default BGP configuration. For the defaults for all characteristics, see the
specific commands in the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols,
Release 12.2.
Table 38-9 Default BGP Configuration
Feature Default Setting
Aggregate address Disabled: None defined.
AS path access list None defined.
Auto summary Enabled.
Best path
• The router considers as-path in choosing a route and does not compare similar
routes from external BGP peers.
• Compare router ID: Disabled.