Administrator Guide

For more information on prefix lists, see IP Prefix Lists.
To enable BFD sessions on specific neighbors, perform the following steps:
Enter the following command to enable BFD session on specific next-hop neighbors:
CONFIGURATION
ip route bfd prefix-list prefix-list-name
The BFD session is established for the next-hop neighbors that are specified in the prefix-list.
• The absence of a prefix-list causes BFD sessions to be enabled on all the eligible next-hop neighbors.
• You can use only valid unicast address prefixes in the BFD prefix list. An erroneous prefix in a prefix-list causes the entire prefix-list to
be rejected.
• A BFD session is enabled for the directly connected next-hop neighbor specified in the configured destination prefix list.
• If you attach an empty prefix-list, all the existing established BFD sessions are teared down. If a destination prefix or prefix range is not
present in the prefix-list, then it is considered as an implicit deny.
• When a destination prefix is deleted from the prefix-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 prefixes in the prefix-list are not pointing
to the same neighbor.
• The permit option enables creation of a BFD session for the specified static destination prefix or prefix range. The system prevents
creation of BFD sessions for all other destination prefixes that are explicitly specified as Deny in the prefix list.
• If other destination prefixes in the prefix-list are pointing to the same neighbor, then the no permit or the deny option on a
particular destination prefix neither creates a BFD session on a neighbor nor removes the static routes from the unicast database.
• BFD sessions created using any one IP prefix list are active at any given point in time. If a new prefix list is assigned, then BFD sessions
corresponding to the older (existing) prefix list are replaced with the newer ones.
• Each time a prefix list is modified, only addition or deletion of new entries in that prefix list are processed for BFD session
establishment or tear down.
Changing Static Route Session Parameters
BFD sessions are configured with default intervals and a default role.
The parameters you can configure are: Desired TX Interval, Required Min RX Interval, Detection Multiplier, and system role. These
parameters are configured for all static routes. If you change a parameter, the change affects 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 final 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.
• Disable BFD for static routes.
CONFIGURATION mode
no ip route bfd [prefix-list prefix-list-name] [interval interval min_rx min_rx multiplier
value role {active | passive}]
Configure BFD for IPv6 Static Routes
BFD offers systems a link state detection mechanism for static routes. With BFD, systems are notified to remove static routes from the
routing table as soon as the link state change occurs, rather than waiting until packets fail to reach their next hop.
Configuring BFD for IPv6 static routes is a three-step process:
1. Enable BFD globally.
2. Configure static routes on both routers on the system (either local or remote).
3. Configure an IPv6 route to connect BFD on the static routes using the ipv6 route bfd command.
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Bidirectional Forwarding Detection (BFD)