0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +---------------+---------------+---------------+---------------+
 |               |               |                               |
 |    Version    | PT_ECHO_REPLY |         PacketLength          |
 |               |               |                               |
 +---------------+---------------+---------------+---------------+
 |                               |               |               |
 |            Reserved           |     Flags     | HeaderLength  |
 |                               |               |               |
 +---------------+---------------+---------------+---------------+
 /                                                               /
 /                        Path Label TLV                         /
 /                                                               /
 +---------------+---------------+---------------+---------------+
 |                                                               |
 |                    Echo Reply Message TLVs                    |
 |                                                               |
 +---------------+---------------+---------------+---------------+