[110479] in North American Network Operators' Group
Re: ? how cisco router handle the out-of-order ICMP echo-reply packets
daemon@ATHENA.MIT.EDU (Steve Bertrand)
Tue Jan 6 08:52:12 2009
Date: Tue, 06 Jan 2009 08:52:02 -0500
From: Steve Bertrand <steve@ibctech.ca>
To: swm@emanon.com
In-Reply-To: <008b01c97000$034defc0$09e9cf40$@com>
Cc: nanog@merit.edu
Errors-To: nanog-bounces@nanog.org
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
Description
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.
Steve
