Concept Guide

LocalAddr RemoteAddr Interface State Rx-int Tx-int Mult VRF Clients
* 13.1.1.1 13.1.1.2 Gi 1/2 Up 200 200 3 2 R
* 23.1.1.1 23.1.1.2 Vl 300 Up 200 200 3 2 R
* 33.1.1.1 33.1.1.2 Vl 301 Up 200 200 3 2 R
Establishing Static Route Sessions on Specic Neighbors
You can selectively enable BFD sessions on specic neighbors based on a destination prex-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 specic next-hop neighbors. You can
specify the next-hop neighbors to be part of a BFD session by including them in a prex-list.
Prex lists are used in route maps and route ltering operations. You can use prex lists as an alternative to existing access lists (ACLs). A
prex is a portion of the IP address. Prex 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 prex list, the prex 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 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.
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Bidirectional Forwarding Detection (BFD)