Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!bloom-beacon!bu-cs!encore!calliope!boykin
From: boykin@calliope.Encore.COM (Joseph Boykin)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: ICMP Multiple Echo Replies
Keywords: ICMP echo reply
Message-ID: <9691@xenna.Encore.COM>
Date: 30 Jun 89 21:19:29 GMT
References: <1131@umn-d-ub.D.UMN.EDU> <25908@agate.BERKELEY.EDU>
Sender: news@Encore.COM
Reply-To: boykin@calliope.UUCP (Joseph Boykin)
Organization: Encore Computer Corp, Marlboro, MA
Lines: 40

In article <1131@umn-d-ub.D.UMN.EDU> tperala@umn-d-ub.D.UMN.EDU (Tim Perala) writes:
>I have been getting strange behaviour when pinging a particular
>host on the Internet.  I have not seen this behaviour with any
>other host.  
>>In article <25908@agate.BERKELEY.EDU> cliff@violet.berkeley.edu (Cliff Frost) writes:
>>Duplicate ICMP Echo Replies are an interesting phenomenon.  I've
>>seen a lot of them and in my experience they have never been caused
>>by errors at the recipient, although that is always a possibility.
...
>I don't think they always mean trouble.  I see them occasionally 
>going across the NSFNet backbone and yet we have no problems
>with the backbone.

The Internet host being talked about is mine, and since I've done must
of the TCP/IP hacking on this system I thought it would be useful
for me to respond.

Firstly, I have also seen multiple ICMP replies from various hosts
(although never from multimax.encore.com).  And as was also suggested,
I've never seen these to cause problems, either when we've recieved
them or in other cases.

Our host is hooked up to the Internet (NEARnet) via a Cisco gateway box.
In doing some experimentation we've found that the real cause of the problem
is that the gateway box is the one duplicating the reply messages.  At this
point we don't know why, but we'll look into it (after the July 4th holiday!).

In case anyone is interested... the system is an Encore Multimax 520 with
eight NS32532 CPUS's (8+MIPS/CPU) running a parallelized version of the MACH
operating system.

----

Joe Boykin
Encore Computer Corp
Vice-Chair, IEEE Computer Societies'
    Technical Activities Board

Internet: boykin@encore.com
UUCP: encore!boykin