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Configuring Aggregate Routes Configuring BGP
page 4-32 OmniSwitch 6800/6850/9000 Advanced Routing Configuration Guide December 2007
Configuring Aggregate Routes
Aggregate routes are used to reduce the size of routing tables by combining the attributes of several differ-
ent routes and allowing a single aggregate route to be advertised to peers.
You cannot aggregate an address (for example, 100.10.0.0) if you do not have at least one more-specific
route of the address (for example, 100.10.20.0) in the BGP routing table.
Aggregate routes do not need to be known to the local BGP speaker.
1 Indicate the address and mask for the aggregate route using the ip bgp aggregate-address command:
-> ip bgp aggregate-address 172.22.2.0 255.255.255.0
2 Optional. When an aggregate route is created BGP does not aggregate the AS paths of all routes
included in the aggregate. However, you may specify that a new AS path be created for the aggregate
route that includes the ASs traversed for all routes in the aggregate. To specify that the AS path also be
aggregated use the ip bgp aggregate-address as-set command. For example:
-> ip bgp aggregate-address 172.22.2.0 255.255.255.0 as-set
3 Optional. By default an aggregate route suppresses the advertisement of all more-specific routes within
the aggregate. This suppression of routes is the function of an aggregate route. However, you can disable
route summarization through the no ip bgp aggregate-address summary-only. For example:
-> no ip bgp aggregate-address 172.22.2.0 255.255.255.0 summary-only
4 Optional. You can manipulate several BGP attributes for routes included in this aggregate route. These
attributes and the corresponding commands used to manipulate them are shown in the table below:
Optional Aggregate Route Attribute Manipulation
5 Once you have finished configuring values for this aggregate route, enable it using the
ip bgp aggregate-address status command. For example:
-> ip bgp aggregate-address 172.22.2.0 255.255.255.0 status enable
BGP Attribute Command
Community list for this aggregate route ip bgp aggregate-address community
Local preference value for this aggregate.
This value overrides the value set in the
ip bgp default-lpref command.
ip bgp aggregate-address local-preference
MED value for this aggregate route. ip bgp aggregate-address metric