Administrator Guide

● 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.
Related Configuration Tasks
● Changing IPv6 Static Route Session Parameters
● Disabling BFD for Static Routes
Bidirectional Forwarding Detection (BFD)
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