BFD for BGP Sessions

BGP sessions experiencing undesired flapping due to BFD

BFD is an intensive protocol that consumes system resources. Specifying a minimum interval for BFD less than 100 milliseconds for Routing Engine-based sessions and less than 10 milliseconds for distributed BFD sessions can cause undesired BFD flapping.

Depending on your network environment, these additional recommendations might apply:

• To prevent BFD flapping during the general Routing Engine switchover event, specify a minimum interval of 5000 milliseconds for Routing Engine-based sessions. This minimum value is required because, during the general Routing Engine switchover event, processes such as RPD, MIBD, and SNMPD utilize CPU resources for more than the specified threshold value. Hence, BFD processing and scheduling is affected because of this lack of CPU resources.
• For BFD sessions to remain up during the dual chassis cluster control link scenario, when the first control link fails, specify the minimum interval of 6000 milliseconds to prevent the LACP from flapping on the secondary node for Routing Engine-based sessions.
• For large-scale network deployments with a large number of BFD sessions, specify a minimum interval of 300 milliseconds for Routing Engine-based sessions and 100 milliseconds for distributed BFD sessions.
• For very large-scale network deployments with a large number of BFD sessions, contact Juniper Networks customer support for more information.
• For BFD sessions to remain up during a Routing Engine switchover event when nonstop active routing (NSR) is configured, specify a minimum interval of 2500 milliseconds for Routing Engine-based sessions. For distributed BFD sessions with NSR configured, the minimum interval recommendations are unchanged and depend only on your network deployment.

Note: EX4600 switches do not support minimum interval values of less than 1 second.

Note: Configuring both BFD and graceful restart for BGP on the same device is counterproductive. When an interface goes down, BFD detects this instantly, stops traffic forwarding and the BGP session goes down whereas graceful restart forwards traffic despite the interface failure, this behavior might cause network issues. Hence we do not recommend configuring both BFD and graceful restart on the same device.

Note: QFX5110, QFX5120, QFX5200, and QFX5210 switches support multihop Bidirectional Forwarding Detection (BFD) inline keep alive support which will enable sessions to be configured at less than 1 second. Performance may vary depending on the system load. 10 inline BFD sessions are supported and can be configured with a timer of 150 x 3 milliseconds. Single-hop sessions are also supported.

For more detailed information, please refer to the following documentation:

https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/topic-map/bfd-for-bgp-session.html