35-60
Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 35 Configuring IP Unicast Routing
Configuring BGP
Beginning in privileged EXEC mode, use these commands to create an aggregate address in the routing
table:
To delete an aggregate entry, use the no aggregate-address address mask router configuration
command. To return options to the default values, use the command with keywords.
Configuring Routing Domain Confederations
One way to reduce the IBGP mesh is to divide an autonomous system into multiple subautonomous
systems and to group them into a single confederation that appears as a single autonomous system. Each
autonomous system is fully meshed within itself and has a few connections to other autonomous systems
in the same confederation. Even though the peers in different autonomous systems have EBGP sessions,
they exchange routing information as if they were IBGP peers. Specifically, the next hop, MED, and
local preference information is preserved. You can then use a single IGP for all of the autonomous
systems.
To configure a BGP confederation, you must specify a confederation identifier that acts as the
autonomous system number for the group of autonomous systems.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
router bgp autonomous-system Enter BGP router configuration mode.
Step 3
aggregate-address address mask Create an aggregate entry in the BGP routing table. The aggregate
route is advertised as coming from the AS, and the atomic aggregate
attribute is set to indicate that information might be missing.
Step 4
aggregate-address address mask as-set (Optional) Generate AS set path information. This command
creates an aggregate entry following the same rules as the previous
command, but the advertised path will be an AS_SET consisting of
all elements contained in all paths. Do not use this keyword when
aggregating many paths because this route must be continually
withdrawn and updated.
Step 5
aggregate-address address-mask
summary-only
(Optional) Advertise summary addresses only.
Step 6
aggregate-address address mask
suppress-map map-name
(Optional) Suppress selected, more specific routes.
Step 7
aggregate-address address mask
advertise-map map-name
(Optional) Generate an aggregate based on conditions specified by
the route map.
Step 8
aggregate-address address mask
attribute-map map-name
(Optional) Generate an aggregate with attributes specified in the
route map.
Step 9
end Return to privileged EXEC mode.
Step 10
show ip bgp neighbors [advertised-routes] Verify the configuration.
Step 11
copy running-config startup-config (Optional) Save your entries in the configuration file.
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