Bgp Maximum Prefix; Configure Discard Extra Paths - Cisco NCS 5500 Series Configuration Manual

Bgp configuration ios xr
Hide thumbs Also See for NCS 5500 Series:
Table of Contents

Advertisement

Implementing BGP
Step 11
commit

BGP Maximum Prefix

The maximum-prefix feature imposes a maximum limit on the number of prefixes that are received from a
neighbor for a given address family. Whenever the number of prefixes received exceeds the maximum number
configured, the BGP session is terminated, which is the default behavior, after sending a cease notification to
the neighbor. The session is down until a manual clear is performed by the user. The session can be resumed
by using the clear bgp command. It is possible to configure a period after which the session can be automatically
brought up by using the maximum-prefix command with the restart keyword. The maximum prefix limit
can be configured by the user. Default limits are used if the user does not configure the maximum number of
prefixes for the address family.
On the same lines, the following describes the actions when the maximum prefix value is changed:
• If the maximum value alone is changed, a route-refresh message is sourced, if applicable.
• If the new maximum value is greater than the current prefix count state, the new prefix states are saved.
• If the new maximum value is less than the current prefix count state, then some existing prefixes are
There is currently no way to control which prefixes are deleted.

Configure Discard Extra Paths

The discard extra paths option in the maximum-prefix configuration allows you to drop all excess prefixes
received from the neighbor when the prefixes exceed the configured maximum value. This drop does not,
however, result in session flap.
The benefits of discard extra paths option are:
• Limits the memory footstamp of BGP.
• Stops the flapping of the peer if the paths exceed the set limit.
When the discard extra paths configuration is removed, BGP sends a route-refresh message to the neighbor
if it supports the refresh capability; otherwise the session is flapped.
• When the router drops prefixes, it is inconsistent with the rest of the network, resulting in possible
Note
• If prefixes are dropped, the standby and active BGP sessions may drop different prefixes.
• The discard extra paths configuration cannot co-exist with the soft reconfig configuration.
Perform this task to configure BGP maximum-prefix discard extra paths.
deleted to match the new configured state value.
routing loops.
Consequently, an NSR switchover results in inconsistent BGP tables.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
BGP Maximum Prefix
25

Hide quick links:

Advertisement

Table of Contents
loading

Table of Contents