Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!usc!cs.utexas.edu!uunet!mcvax!ukc!etive!iain
From: iain@etive.ed.ac.uk (Iain Lindsay)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: ICMP Multiple Echo Replies
Summary: Dodgy Hardware ?
Keywords: ICMP echo reply
Message-ID: <2469@etive.ed.ac.uk>
Date: 30 Jun 89 08:48:59 GMT
References: <1131@umn-d-ub.D.UMN.EDU>
Reply-To: iain@ee.ed.ac.uk (Iain Lindsay)
Organization: Edinburgh University Electrical Engineering
Lines: 9

I have observed multiple echo replies when using an old 3com ethernet V1.0
interface on one of our vaxes.  What appears to happen is that the interface
sends a packet, which is then followed on the wire by a packet from another
machine, with minimal packet spacing.  The 3com i/f erroneously thinks the two
packets collided and flags an error, causing the packet to be retransmitted.
Thus, the target host sees two identical packets and sends two replies.  There
are probably numerous other mechanisms which can duplicate packets and which do
not invlove dogdy hardware.
-Iain..