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From: karn@FALINE.BELLCORE.COM (Phil R. Karn)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: ..."layering violations"
Message-ID: <8710291906.AA15222@faline.bellcore.com>
Date: Thu, 29-Oct-87 14:06:28 EST
Article-I.D.: faline.8710291906.AA15222
Posted: Thu Oct 29 14:06:28 1987
Date-Received: Thu, 5-Nov-87 04:39:38 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 13

>Phil,	ICMP messages DO conatin an IP source address of the gateway
>which sent the message - look in the IP header's Source Address field.

Yes, I know they're *supposed* to. I meant to say that I've seen many
gateways use the destination IP address of the original datagram as the
source address for the IP datagram containing the ICMP message, and this
makes it impossible to discern where the problem is.

One implementation around here returns every broadcast it sees with
a "port unreachable" ICMP message and puts the IP broadcast address in
the IP source field!

Phil