IP in IP - Handling ICMP Messages

Handling ICMP Messages

After sending a datagram, there may be chances of encapsulator getting ICMP messages from intermediate nodes. The encapsulator takes action for ICMP message depending on the Type and Code of the ICMP messages. The following are the ICMP messages with Type and Code as well as the action taken by the encapsulator:

  • Destination Unreachable (Type 3)
    • Network Unreachable (Code 0) – ICMP error message with Type 3 Code 0 should be sent to original sender.
    • Host Unreachable (Code 1) – ICMP error message with Type 3 Code 0 should be sent to original sender.
    • Protocol Unreachable (Code 2) – ICMP error message with Type 3 Code 0 or 1 should be sent to original sender.
    • Port Unreachable (Code 3) – No ICMP error message should be sent to original sender.
    • Datagram too big (Code 4) – ICMP error message with Type 3 Code 4 should be sent to original sender.
    • Source Route Failed (Code 5) – No ICMP error message should be sent to original sender.
  • Source Quence (Type 4) – No ICMP error message should be sent to original sender
  • Redirect (Type 5) – No ICMP error message should be sent to original sender
  • Time Exceeded (Type 6) – ICMP error message with Type 3 Code 1 should be sent to original sender (Case of Routing loops within tunnels)
  • Parameter Problem (Type 12)
    • If the error message points to a field copied from unencapsulated datagram, then the ICMP error message should be sent to original sender.
    • If the error message points to a field inserted by encapsulator, then the ICMP error message should not be sent to original sender

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