порт будет тот же
BFD packets received on tails for an IP multicast group MUST be consumed by tails and MUST NOT be forwarded to receivers. Nodes with the BFD session of type MultipointTail MUST identify packets received on an IP multipoint path as a BFD Control packet if the destination UDP port value equals 3784.
Т.е. для капетов используется DST IP == MCAST DST, c MPLS такая постанова:
For multipoint LSPs, when IP/UDP encapsulation of BFD Control packets is used, MultipointTail MUST expect destination UDP port 3784. The destination IP address of a BFD Control packet MUST be in the 127.0.0.0/8 range for IPv4 or in the 0:0:0:0:0:FFFF:7F00:0/104 range for IPv6. The use of these destination addresses is consistent with
the explanations and usage in [RFC8029].