4.2.3.9 ICMP Messages

TCP MUST act on an ICMP error message passed up from the IP layer, directing it to the connection that created the error. The necessary demultiplexing information can be found in the IP header contained within the ICMP message.

• Source Quench

  TCP MUST react to a Source Quench by slowing transmission on the connection. The RECOMMENDED procedure is for a Source Quench to trigger a "slow start," as if a retransmission timeout had occurred.

• Destination Unreachable -- codes 0, 1, 5

  Since these Unreachable messages indicate soft error conditions, TCP MUST NOT abort the connection, and it SHOULD make the information available to the application.

  DISCUSSION:

  TCP could report the soft error condition directly to the application layer with an upcall to the ERROR_REPORT routine, or it could merely note the message and report it to the application only when and if the TCP connection times out.

• Destination Unreachable -- codes 2-4

  These are hard error conditions, so TCP SHOULD abort the connection.

• Time Exceeded -- codes 0, 1

  This should be handled the same way as Destination Unreachable codes 0, 1, 5 (see above).

• Parameter Problem

  This should be handled the same way as Destination Unreachable codes 0, 1, 5 (see above).