When BFD for Layer 3 protocols is configured on VE interfaces, one of the physical ports is chosen to set up the session. This physical port is allocated after Address Resolution Protocol (ARP) is resolved for that neighbor. For more information, see ARP Overview.
If a member of a VE port goes down and a new egress port is identified, the session is moved to another physical port. If a new egress port is not identified, BFD tries to locate a destination IPv4 or IPv6 address. If the new egress port is not learned during the BFD detection time, the session is declared as down.