Concept Guide
Establishing Static Route Sessions on Specic Neighbors
You can selectively enable BFD sessions on specic neighbors based on a destination prex-list.
When you establish a BFD session using the ip route bfd command, all the next-hop neighbors in the static route become part of the
BFD session. Starting with Dell EMC Networking OS release 9.11.0.0, you can enable BFD sessions on specic next-hop neighbors. You can
specify the next-hop neighbors to be part of a BFD session by including them in a prex-list.
Prex lists are used in route maps and route ltering operations. You can use prex lists as an alternative to existing access lists (ACLs). A
prex is a portion of the IP address. Prex lists constitute any number of bits in an IP address starting from the far left bit of the far left
octet. By specifying the exactly number of bits in an IP address that belong to a prex list, the prex list can be used to aggregate
addresses and perform some functions; for example, redistribution.
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 specied prex list or prex 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 specied prex list or prex list range.
For more information on prex lists, see IP Prex Lists.
To enable BFD sessions on specic neighbors, perform the following steps:
Enter the following command to enable BFD session on specic next-hop neighbors:
CONFIGURATION
ip route bfd prefix-list prefix-list-name
The BFD session is established for the next-hop neighbors that are specied in the prex-list.
• The absence of a prex-list causes BFD sessions to be enabled on all the eligible next-hop neighbors.
• You can use only valid unicast address prexes in the BFD prex list. An erroneous prex in a prex-list causes the entire prex-list to be
rejected.
• A BFD session is enabled for the directly connected next-hop neighbor specied in the congured destination prex list.
• If you attach an empty prex-list, all the existing established BFD sessions are teared down. If a destination prex or prex range is not
present in the prex-list, then it is considered as an implicit deny.
• When a destination prex is deleted from the prex-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 prexes in the prex-list are not pointing to
the same neighbor.
• The permit option enables creation of a BFD session for the specied static destination prex or prex range. The system prevents
creation of BFD sessions for all other destination prexes that are explicitly specied as Deny in the prex list.
• If other destination prexes in the prex-list are pointing to the same neighbor, then the no permit or the deny option on a
particular destination prex neither creates a BFD session on a neighbor nor removes the static routes from the unicast database.
• BFD sessions created using any one IP prex list are active at any given point in time. If a new prex list is assigned, then BFD sessions
corresponding to the older (existing) prex list are replaced with the newer ones.
• Each time a prex list is modied, only addition or deletion of new entries in that prex list are processed for BFD session establishment
or tear down.
Changing Static Route Session Parameters
BFD sessions are congured with default intervals and a default role.
The parameters you can congure are: Desired TX Interval, Required Min RX Interval, Detection Multiplier, and system role. These
parameters are congured for all static routes. If you change a parameter, the change aects all sessions for static routes.
To change parameters for static route sessions, use the following command .
• Change parameters for all static route sessions.
Bidirectional Forwarding Detection (BFD)
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