The SR OS supports IP/UDP encapsulation for BFD. With this encapsulation type, the UDP headers are included on the BFD packet. IP/UDP encapsulation is supported for pseudowires that use router alert (VCCV Type 2), and for pseudowires with a control word (VCCV Type 1). In the control word case, the IPv4 channel (channel type 0x0021) is used. On the node, the destination IPv4 address is fixed at 127.0.0.1 and the source address is 127.0.0.2.
VCCV BFD sessions run end-to-end on a switched pseudowire. They do not terminate on an intermediate S-PE; therefore, the TTL of the pseudowire label on VCCV BFD packets is always set to 255 to ensure that the packets reach the far-end T-PE of an MS-PW.