Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!decvax!decwrl!ucbvax!SH.CS.NET!dennis
From: dennis@SH.CS.NET.UUCP
Newsgroups: mod.protocols.tcp-ip
Subject: Re: 127.0.0.1
Message-ID: <8607180653.AA18071@ucbvax.Berkeley.EDU>
Date: Fri, 18-Jul-86 02:55:37 EDT
Article-I.D.: ucbvax.8607180653.AA18071
Posted: Fri Jul 18 02:55:37 1986
Date-Received: Fri, 18-Jul-86 17:53:38 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 22
Approved: tcp-ip@sri-nic.arpa

Hans, everybody,

There's a bug (*not* a feature!) in the 4.2 network code that assigns the
source address of a packet to be some single IP interface on that machine
(in fact, it binds the local address too early, before the packet or
connection has been routed).  For incoming TCP connections, there is no
problem; the local address is specified by the host that initiates the
connection.  For outgoing UDP packets, the first interface in the interface
list (given by netstat -i) is usually used (although the loopback interface
{which uses 127.0.0.1 as its address} is most often the last listed
interface).

CSNET requires that X25net sites install this fix; during installation and
checkout, we most often do not tell our kernel how to reach a site's local
network.  This causes TCP connections from our new site to the Internet fail
while connections from the Internet to the new site work.

There are fixes for this available from BRL (at least, that's where I got
them).  Mike?  Are they in anonymous FTP?

Dennis Rockwell
CSNET Technical Staff