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List:       opensolaris-networking-discuss
Subject:    Re: [networking-discuss] [brussels-dev] shrinking the ndd
From:       James Carlson <james.d.carlson () Sun ! COM>
Date:       2009-02-27 15:10:05
Message-ID: 18856.589.209428.382388 () gargle ! gargle ! HOWL
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Darren Reed writes:
> On 26/02/09 07:57 PM, Sowmini.Varadhan@Sun.COM wrote:
> > I don't know.. smells like a huge copy/paste project here :-)
> 
> I can easily imagine, back when Solaris first arrived with a TTL
> of 255, that they wanted to provide a knob in case some piece of
> network hardware reacted badly because of a bug that assumed 255 == -1.

I don't think this is the sort of thing that necessarily requires
imagination.  A quick trip through memory lane (also known as the SCCS
history ;-}) shows that all of the following parameters were added
with the IPv6 project in 1999:

  ip6_def_hops
  tcp_ipv4_ttl
  tcp_ipv6_hoplimit
  icmp_ipv4_ttl
  icmp_ipv6_hoplimit
  udp_ipv4_ttl
  udp_ipv6_hoplimit

Many of the folks involved with that project are still around and can
probably answer why they added these parameters.  (Unfortunately, I
don't know where that old project gate might be, if it still exists at
all.  That would probably have better records.)

My guess, if we're just guessing, is that they were added on spec:
someone thought that they might be useful somewhere down the road.  If
we're doing a clean-up project here, then it's probably high time to
figure out whether that initial speculation panned out.  If they're
not useful, then toss 'em.

These two are special:

  ip_def_ttl		- SID 1.5 ip.c, November 1991 Mentat update
  ip_broadcast_ttl	- CR 1162269

That first one seems like it could be related to some RFC issue
(though not clear what).  That second one (thankfully) has a record.

-- 
James Carlson, Solaris Networking              <james.d.carlson@sun.com>
Sun Microsystems / 35 Network Drive        71.232W   Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757   42.496N   Fax +1 781 442 1677
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