Express Forwarding Commands on Cisco ASR 9000 Series Router module in the Cisco ASR 9000 Series
Aggregation Services Router IP Addresses and Services Command Reference for details on BGP policy
accounting.
Table policy also provides the ability to drop routes from the RIB based on match criteria. This feature can
be useful in certain applications and should be used with caution as it can easily create a routing ‘black hole’
where BGP advertises routes to neighbors that BGP does not install in its global routing table and forwarding
table.
Update Groups
The BGP Update Groups feature contains an algorithm that dynamically calculates and optimizes update
groups of neighbors that share outbound policies and can share the update messages. The BGP Update Groups
feature separates update group replication from peer group configuration, improving convergence time and
flexibility of neighbor configuration.
To use this feature, you must understand the following concepts:
Related Topics
BGP Update Generation and Update Groups , on page 33
BGP Update Group , on page 33
BGP Update Generation and Update Groups
The BGP Update Groups feature separates BGP update generation from neighbor configuration. The BGP
Update Groups feature introduces an algorithm that dynamically calculates BGP update group membership
based on outbound routing policies. This feature does not require any configuration by the network operator.
Update group-based message generation occurs automatically and independently.
BGP Update Group
When a change to the configuration occurs, the router automatically recalculates update group memberships
and applies the changes.
For the best optimization of BGP update group generation, we recommend that the network operator keeps
outbound routing policy the same for neighbors that have similar outbound policies. This feature contains
commands for monitoring BGP update groups.
BGP Cost Community
The BGP cost community is a nontransitive extended community attribute that is passed to internal BGP
(iBGP) and confederation peers but not to external BGP (eBGP) peers. The cost community feature allows
you to customize the local route preference and influence the best-path selection process by assigning cost
values to specific routes. The extended community format defines generic points of insertion (POI) that
influence the best-path decision at different points in the best-path algorithm.
The cost community attribute is applied to internal routes by configuring the set extcommunity cost command
in a route policy. See the Routing Policy Language Commands on Cisco ASR 9000 Series Router module
of Cisco ASR 9000 Series Aggregation Services Router Routing Command Reference for information on the
set extcommunity cost command. The cost community set clause is configured with a cost community ID
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
OL-30423-03 33
Implementing BGP
Update Groups
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