Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BGP AND MPLS CONFIGURATION GUIDE 2010-10-12 Configuration Manual page 162

JunosE 11.3.x BGP and MPLS Configuration Guide
bgp graceful-restart
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Note that the receiving peer does not defer its best-path selection process while waiting
for a restarted peer to reestablish a session. The receiving peer continues to use the stale
routes from the restarted peer in the decision process. When it flushes stale routes, the
receiving peer then uses the freshly updated routes.
A restarting peer must bring the session back up and refresh its routes within a limited
period, or BGP on the receiving peer will flush all the stale routes. When a BGP speaker
advertises the graceful restart capability, it also advertises how long it expects to take
to reestablish a session if it restarts. If the session is not reestablished within this restart
period, the speaker's peers flush the stale routes from the speaker. You can use the bgp
graceful-restart restart-time command to modify the restart period advertised to all
peers; the neighbor graceful-restart restart-time command modifies the restart period
advertised to specific peers or peer groups. A receiving peer starts the timer as soon as
it recognizes that the session with the restarting peer has transitioned to down.
The receiving peer also has a configurable timer that starts when it recognizes that the
session with the restarting peer has gone down. The bgp graceful-restart stalepaths-time
command determines how long a receiving peer is willing to use stale paths from any
restarted peer; the neighbor graceful-restart stalepaths-time command does the same
for a specified restarted peer or peer group. If the receiving peer does not receive an
End-of-RIB marker from the restarted peer before the stalepaths timer expires, the
receiving peer flushes all stale routes from the peer.
In this release, BGP supports the graceful restart capability to inform peers that the
forwarding state for IPv6 address families, namely unicast, multicast, VPN unicast, and
unicast labeled subsequent address family identifiers (SAFIs), can be preserved during
a stateful SRP switchover. MPLS also provides high availability support for IPv6 by
preserving the MPLS state for IPv6 interfaces during a stateful SRP switchover. This
capability of MPLS enables BGP to support graceful restart for IPv6 labeled address
families. During a restart, BGP acts as a restarting speaker for the IPv6 unlabeled and
labeled address-families. The function of BGP as a graceful restart helper for both IPv4
and IPv6 address families had been available in lower-numbered releases, and there is
no change to this functionality in this release.
NOTE: The function of BGP as a graceful restart helper for both IPv4 and
IPv6 address families had been available in lower-numberered releases, and
there is no change to this functionality in this release.
Use to enable the BGP graceful restart capability.
Advertisement of the graceful restart capability is disabled by default.
The no neighbor capability negotiation command prevents the advertisement of all
BGP capabilities, including graceful restart, to the specified peers.
This command takes effect immediately and automatically bounces the session.
Example
host1(config-router)#bgp graceful-restart
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