BFD sessions established over the IRB with no physical interface part of the bridge-domain/ethernet-table in EVPN-VXLAN setup will be running in centralized mode ( non-distributed mode )

The BFD session that are established over the IRB in EVPN-VXLAN setup with no physical interfaces part of the bridge-domain/ethernet-table (only vtep interfaces) will be working in centralized mode instead of distributed mode .

If the RE (Routing Engine) CPU is very busy for any reason, i.e. due to a network churn and the BFD times are set aggressively , the BFD sessions running over IRB may flap since the sessions are not distributed

In order to move the BFD sessions to distributed mode in such setup we need to add a physical interfaces to be part of the bridge-domain/ethernet-table

Understanding How BFD Detects Network Failures