Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!DAINICHI.TN.CORNELL.EDU!swb
From: swb@DAINICHI.TN.CORNELL.EDU (Scott Brim)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: What is INADDR_LOOPBACK for in sockets?
Message-ID: <8912040250.AA01269@chumley.TN.Cornell.EDU>
Date: 4 Dec 89 02:50:44 GMT
References: <17748@ea.ecn.purdue.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 24


   >Date: 2 Dec 89 15:15:27 GMT
   >From: ea.ecn.purdue.edu!housel@ee.ecn.purdue.edu  (Peter S. Housel)
   >Subject: Re: What is INADDR_LOOPBACK for in sockets?
   >To: tcp-ip@nic.ddn.mil
   >
   >	The nifty thing is that (on many systems with BSD-derived
   >networking) you can disable the loopback-net, through which address
   >127.0.0.1 is routed. Running "ifconfig lo0 down" will disable the
   >"loopback interface" and the machine will be unable to talk to itself.

I can't resist adding that you have to be careful, though, of
situations where you lose a route to 127.0.0.1 but you have a
"default" route floating around your net.  For example, I used to see
not infrequent situations where a BSD Unix-based router would be
generating a "default" route -- say because it was EGPing with a
backbone -- and on a broken system further away from the backbone,
sendmail would try to connect to 127.0.0.1, and would end up following
the default route and accidentally connecting to the
default-generating machine (which knew where "127.0.0.1" was --
itself!), so that all mail from the broken one would appear to be from
the correct userid but the incorrect system (the default-generating
one).
							Scott


Brought to you by Super Global Mega Corp .com