Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!cornell!uw-beaver!rice!sun-spots-request
From: slevy@nic.mr.net (Stuart Levy)
Newsgroups: comp.sys.sun
Subject: Re: FTP problem on 3/60's
Message-ID: <8812171950.AA26770@nic.MR.NET>
Date: 30 Dec 88 01:56:01 GMT
Sender: usenet@rice.edu
Organization: Sun-Spots
Lines: 20
Approved: Sun-Spots@rice.edu
Original-Date: Sat, 17 Dec 88 13:50:43 CST
X-Sun-Spots-Digest: Volume 7, Issue 78, message 5 of 10

> We had this problem when a ypclient machine did not have its own host name
> in its own version of /etc/hosts.  This also disabled the "talk" program.
> To fix, add the host name to /etc/hosts and reboot.  Apparently, something
> in the kernel looks at /etc/hosts at boot time.

What's happening here is that the reverse-ARP code, which diskless Suns
use to find their addresses at boot time, is sloppy.  The address is
stored in a 16-byte struct sockaddr_in, including a 4-byte internet
address and 8 bytes of zero padding.  The RARP code fills in the IP
address but doesn't zero the 8 pad bytes.  This works for many things, but
if you try to bind() a socket to a specific IP address as ftpd and talkd
do, it fails unless those pad bytes are really zero.

They normally get cleared by the "ifconfig ??0 $hostname" in /etc/rc.boot.
But if the local /etc/hosts doesn't list whatever you have for hostname --
or if it does list it but at an IP address *different* from the one picked
up by the RARP code -- the ifconfig fails, and ftpd etc. report strange
errors.

	Stuart Levy