Bgp Update Group; Bgp Cost Community Reference; Bgp Next Hop Reference - Cisco NCS 5500 Series Configuration Manual

Information about Implementing BGP

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 Reference

The cost community attribute is applied to internal routes by configuring the set extcommunity cost command
in a route policy. The cost community set clause is configured with a cost community ID number (0–255)
and cost community number (0–4294967295). The cost community number determines the preference for the
path. The path with the lowest cost community number is preferred. Paths that are not specifically configured
with the cost community number are assigned a default cost community number of 2147483647 (the midpoint
between 0 and 4294967295) and evaluated by the best-path selection process accordingly. When two paths
have been configured with the same cost community number, the path selection process prefers the path with
the lowest cost community ID. The cost-extended community attribute is propagated to iBGP peers when
extended community exchange is enabled.
The following commands include the route-policy keyword, which you can use to apply a route policy that
is configured with the cost community set clause:
• aggregate-address
• redistribute
• network

BGP Next Hop Reference

Event notifications from the RIB are classified as critical and noncritical. Notifications for critical and noncritical
events are sent in separate batches. BGP is notified when any of the following events occurs:
• Next hop becomes unreachable
• Next hop becomes reachable
• Fully recursed IGP metric to the next hop changes
• First hop IP address or first hop interface change
• Next hop becomes connected
• Next hop becomes unconnected
• Next hop becomes a local address
• Next hop becomes a nonlocal address
Note Reachability and recursed metric events trigger a best-path recalculation.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
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Implementing BGP