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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
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Chapter38 Configuring IP Unicast Routing
Configuring BGP
In BGP, each route consists of a network number, a list of autonomous systems that information ha s
passed through (the autonomous system path), and a list of other path attributes. The primary function
of a BGP system is to exchange network reachability information, including information about the list
of AS paths, with other BGP systems. This information can be used to determine AS connectivity, to
prune routing loops, and to enforce AS-level policy decisions.
A router or switch running Cisco IOS does not select or use an IBGP route unless it has a route available
to the next-hop router and it has received synchronization from an IGP (unless IGP sy nchro niza tion is
disabled). When multiple routes are available, BGP bases its path selection on attribute values. See the
“Configuring BGP Decision Attributes” section on page 38-53 for information about BGP attributes.
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, page38-57
•Configuring BGP Community Filtering, page38-58
•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, page38-64
For detailed descriptions of BGP configuration, see the “Configuring BGP” chapter in the “IP R outi ng
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.
For a list of BGP commands that are visible but not supported by the switch, see Appendix C,
“Unsupported Commands in Cisco IOS Release 12.2(40)EX1.”
Default BGP Configuration
Table38-9 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,
Release12.2.