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