[110481] in North American Network Operators' Group
RE: ? how cisco router handle the out-of-order ICMP echo-reply packets
daemon@ATHENA.MIT.EDU (Scott Morris)
Tue Jan 6 08:59:20 2009
From: "Scott Morris" <swm@emanon.com>
To: "'Steve Bertrand'" <steve@ibctech.ca>
In-Reply-To: <49636202.6030000@ibctech.ca>
Date: Tue, 6 Jan 2009 08:58:33 -0500
Cc: nanog@merit.edu
Reply-To: swm@emanon.com
Errors-To: nanog-bounces@nanog.org
Guess I'll have to go back and look at wireshark output again... I didn't
recall seeing sequence number used in pings between Cisco devices, although
that may just be the implementation ('may be used') part.
I'll stand corrected. ;)
Scott
-----Original Message-----
From: Steve Bertrand [mailto:steve@ibctech.ca]
Sent: Tuesday, January 06, 2009 8:52 AM
To: swm@emanon.com
Cc: 'Zhao Ping'; nanog@merit.edu
Subject: Re: ? how cisco router handle the out-of-order ICMP echo-reply
packets
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
