Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!njin!princeton!phoenix!jsm
From: jsm@phoenix.Princeton.EDU (John Scott McCauley Jr.)
Newsgroups: comp.protocols.tcp-ip
Subject: Small TTL values evaporate in large networks (actually IPTTLDEC)
Message-ID: <8770@phoenix.Princeton.EDU>
Date: 29 May 89 19:59:46 GMT
References: <8905242046.AA20920@sirius.cc.utexas.edu> <8905251324.AA24553@sirius.cc.utexas.edu>
Reply-To: jsm@phoenix.Princeton.EDU (John Scott McCauley Jr.)
Organization: Princeton University, NJ
Lines: 21

A similar problem: at least one BSDish implementation of TCP I've seen
had IPTTLDEC set to 5, not 1. (IPTTLDEC apparantly is the number that gets
subtracted from a packet's TTL when the machine forwards the packet -- it
also serves as the minimum ttl value that a packet can have before sending an
ICMP TTL_EXCEEDED message I think.)

This wasn't too much of a problem as the machine wasn't a gateway. However,
another machine on the local net was sending out broadcast packets with a
TTL of 3 (don't know why), so the first machine was the only machine on
the net sending out ICMP TTL_EXCEEDED messages.

I did a binary patch to change IPTTLDEC to 1 (in two places) and the
problem went away.

	Scott

-- 
Scott McCauley, jsm@phoenix.princeton.edu (INTERNET)
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