ICMP

The following ICMPv4 messages are supported in MAP-T on the VSR; other types of ICMP messages are not supported:

• ICMP query messages

  These messages contain an identifier field in the ICMP header, which is referred to as the ‟query identifier” or ‟query-id” and it is used in MAP-T in the same way as the L4 ports are used in TCP or UDP. ICMP Echo Req/Rep (PING) and traceroute are examples that rely on ICMP Query messages.

• ICMP error messages

  These messages contain the embedded original datagram that triggers the ICMP error message. The ICMP error messages do not contain the query-id field.

The ICMP Query messages and ICMP Error messages are supported regardless of whether they are just passing through a VSR (transit messages), or are terminated or generated in or from a VSR.

The NAT-related ICMPv4 behavior is described in RFC 5508. The following NAT messages are supported in the MAP-T VSR (RFC 5508, §7, Requirement 10a):

• ICMPv4 Error Message: Destination Unreachable Message (Type 3)

• ICMPv4 Error Message: Time Exceeded Message (Type 11)

• ICMPv4 Query Message: Echo and Echo Reply Messages (Type 8 and Type 0)