Administrator Guide

You can use the following options to enable or disable the BFD session:
• Permit – The permit option enables creation of a BFD session on the specied prex list or prex list range. The no permit option
enables tear down of the BFD session if and only if the ACL has no permit entry that shares the same neighbor.
• Deny – The deny option prevents BFD sessions from getting created for the specied prex list or prex list range.
For more information on prex lists, see IP Prex Lists.
To enable BFD sessions on specic neighbors, perform the following steps:
Enter the following command to enable BFD session on specic next-hop neighbors:
CONFIGURATION
ip route bfd prefix-list prefix-list-name
The BFD session is established for the next-hop neighbors that are specied in the prex-list.
• The absence of a prex-list causes BFD sessions to be enabled on all the eligible next-hop neighbors.
• You can use only valid unicast address prexes in the BFD prex list. An erroneous prex in a prex-list causes the entire prex-list to be
rejected.
• A BFD session is enabled for the directly connected next-hop neighbor specied in the congured destination prex list.
• If you attach an empty prex-list, all the existing established BFD sessions are teared down. If a destination prex or prex range is not
present in the prex-list, then it is considered as an implicit deny.
• When a destination prex is deleted from the prex-list using the no permit option, the corresponding BFD session is torn down
immediately. In this scenario, the BFD session tear down occurs only if the other destination prexes in the prex-list are not pointing to
the same neighbor.
• The permit option enables creation of a BFD session for the specied static destination prex or prex range. The system prevents
creation of BFD sessions for all other destination prexes that are explicitly specied as Deny in the prex list.
• If other destination prexes in the prex-list are pointing to the same neighbor, then the no permit or the deny option on a
particular destination prex neither creates a BFD session on a neighbor nor removes the static routes from the unicast database.
• BFD sessions created using any one IP prex list are active at any given point in time. If a new prex list is assigned, then BFD sessions
corresponding to the older (existing) prex list are replaced with the newer ones.
• Each time a prex list is modied, only addition or deletion of new entries in that prex list are processed for BFD session establishment
or tear down.
Changing Static Route Session Parameters
BFD sessions are congured with default intervals and a default role.
The parameters you can congure are: Desired TX Interval, Required Min RX Interval, Detection Multiplier, and system role. These
parameters are congured for all static routes. If you change a parameter, the change aects all sessions for static routes.
To change parameters for static route sessions, use the following command .
• Change parameters for all static route sessions.
CONFIGURATION mode
ip route bfd [prefix-list prefix-list-name] interval milliseconds min_rx milliseconds
multiplier value role [active | passive]
To view session parameters, use the show bfd neighbors detail command.
Disabling BFD for Static Routes
If you disable BFD, all static route BFD sessions are torn down.
A nal Admin Down packet is sent to all neighbors on the remote systems, and those neighbors change to the Down state.
To disable BFD for static routes, use the following command.
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Bidirectional Forwarding Detection (BFD)