? how cisco router handle the out-of-order ICMP echo-reply packets

Steve Bertrand steve at ibctech.ca
Tue Jan 6 13:52:02 UTC 2009

Scott Morris wrote:
> There aren't sequence numbers with ICMP.  And the timeout value is
> watched/triggered before the next ICMP is sent, so there shouldn't really be
> any ordering problem/interpretation anyway.

FYI, from RFC 792:

  Sequence Number


      The data received in the echo message must be returned in the echo
      reply message.

      The identifier and sequence number may be used by the echo sender
      to aid in matching the replies with the echo requests.  For
      example, the identifier might be used like a port in TCP or UDP to
      identify a session, and the sequence number might be incremented
      on each echo request sent.  The echoer returns these same values
      in the echo reply.


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