Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!proteon.com!jas
From: jas@proteon.com (John A. Shriver)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Small TTL values evaporate in large networks
Message-ID: <8905242135.AA26778@monk.proteon.com>
Date: 24 May 89 21:35:26 GMT
References: <8905241815.AA15718@sirius.cc.utexas.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 36

Neither value is correct.  It is clearly called out in RFC 793 (TCP)
to be sixty (60).  To quote:

  TCP/Lower-Level Interface

    The TCP calls on a lower level protocol module to actually send and
    receive information over a network.  One case is that of the ARPA
    internetwork system where the lower level module is the Internet
    Protocol (IP) [2].

    If the lower level protocol is IP it provides arguments for a type
    of service and for a time to live.  TCP uses the following settings
    for these parameters:

      Type of Service = Precedence: routine, Delay: normal, Throughput:
      normal, Reliability: normal; or 00000000.

      Time to Live    = one minute, or 00111100.

        Note that the assumed maximum segment lifetime is two minutes.
        Here we explicitly ask that a segment be destroyed if it cannot
        be delivered by the internet system within one minute.

Thus, neither 4.2bsd (15) nor 4.3bsd (30) is correct.  (Why fix a bug
with another bug?)

You can do a quick check by examining the value of TCP_TTL in
/usr/sys/netinet/tcp_timer.h, but there is no guaruntee that your
vendor compiled the kernel using this file.

In SunOS 3.5.2, the value has been increased to 30, which is not so
bad a bug.

The TTL was still 15 on Ultrix-32 V2.2.  I reported it in SPR
487999/ICA-16612.  I got patches for three kernel files.  I presume
that it is fixed in V3.0.