A traceroute mechanism enables responses to the traceroute to reach the
originating router (originator) along a multihop pseudowire (PW). A
traceroute message includes an accumulator operable to count hops along a
MH-PW, implemented as a time-to-live (TTL) field, as is known in the art.
An originator router employs multiple TTL values, and decrements one of
the TTL "accumulators" for each hop. At the ultimate (terminal) router
defining the end of the multihop PW, a TTL in the return message is set
to the number of hops traveled by the traceroute. The difference between
the accumulator and the initial TTL value determines the number of hops
traveled by the traceroute message, and hence the number of hops back to
the originating node. The traceroute return message, now having a TTL set
to the number of hops of the counterpart traceroute, reaches the
originator when the TTL value is decremented to zero.