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JunosE 11.2.x BGP and MPLS Configuration Guide
BFD and BGP Graceful Restart
140
the minimum receive interval and the minimum transmit interval to the same value.
The default value is 300 milliseconds.
You can use the multiplier keyword to specify the detection multiplier value. The
calculated BFD liveness detection interval can be different on each peer. The multiplier
value is roughly equivalent to the number of packets that can be missed before the
BFD session is declared to be down. The default value is 3.
For details on liveness detection negotiation, see JunosE IP Services Configuration Guide.
You can change the BFD liveness detection parameters at any time without stopping
or restarting the existing session; BFD automatically adjusts to the new parameter
value. However, no changes to BFD parameters take place until the values resynchronize
with each peer.
If you specify a BGP peer group by using the peerGroupName argument, all the members
of the peer group inherit the characteristic configured with this command unless it is
overridden for a specific peer.
This command takes effect immediately.
The BGP session does not flap when you enable BFD for a session that is already up
or change the BFD timer values for an established session.
If you remove the BFD configuration while the BGP sessions and the BFD protocol
session are up, BFD moves to the Admin Down state and communicates the change
to the peer to enable the client protocols to handle this in a seamless manner without
going down. For the Admin Down state to work, the peer, which receives the Admin
Down state notification, must have the capability to distinguish between
administratively down state and real link down.
NOTE: The BFD Admin Down state is used to bring down a BFD session administratively,
to protect client applications from BFD configuration removal, license issues, and
clearing of BFD sessions.
Use the no version to disable BFD liveness detection for the neighbor. Use the default
version to remove the explicit configuration from the peer or peer group and reestablish
inheritance of the feature configuration.
See neighbor bfd-liveness-detection.
So that BFD can maintain its BFD protocol sessions across a BGP graceful restart, BGP
requests that BFD set the C bit to 1 in transmitted BFD packets. When the C bit is set to
1, BFD can maintain its session in the forwarding plane in spite of disruptions in the control
plane. Setting the bit to 1 gives BGP neighbors acting as a graceful restart helper the most
accurate information about whether the forwarding plane is up.
When BGP is acting as a graceful restart helper and the BFD session to the BGP peer is
lost, one of the following actions takes place:
Copyright © 2010, Juniper Networks, Inc.
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