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Date: Fri, 17 Nov 1995 15:25:25 -0500
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Organization: Cybernet Systems Corporation
From: "Mark J. Taylor" <root@spiffy.cybernet.com>
To: <hackers@freebsd.org>
Subject: gethostbyXXX() blocking too long
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For quite some time now, our site has been plagued by long delays
during connecting to machines on the Internet.  The connection is
established quickly, followed by LONG delays in getting any data,
login prompt, etc.  I think that I've stumbled upon the answer.

Many services (ftpd, telnetd, rshd, etc.) perform a gethostbyaddr()
call right after a connection is established.  Of course, this
call blocks until the nameserver(s) are asked to reverse-name
resolve the IP address string.  Well, it turns out that our site
(at least) does not have any reverse name entries in our primary
Internet name servers (we have them here locally, but our DNS
primaries do not point to our DNS).  Therefore, any program on any
machine on the Internet will BLOCK until the DNS queries time out,
which takes anywhere from 60 to 240 seconds.

For example:

mymachine FTPs to oak.oakland.edu
inetd on oak.oakland.edu starts up a ftpd
(socket is established)
ftpd on oak does a gethostbyaddr() call on mymachine's IP address
DNS stuff starts
LONG DELAY
DNS times out (no replies)
ftpd continues, logs IP address instead of hostname


There are two ways that I can see to fix this problem:
1) get the reverse name entries in one of our primary Internet
   DNS servers
2) call alarm()/setitimer() before any blocking DNS calls
   (gethostbyname, gethostbyaddr) with a small time value
   (10 seconds or so) in all software that performs these calls
   (this would be a change in the remote site's software)

Of course, (2) will require the everyone to modify their software.  :)
(some already have, so it would seem)

So, am I totally wrong in requesting that change (2) go into FreeBSD
daemons, so that at least when someone at sites w/o reverse DNS
lookup entries connects to FreeBSD machines, there will not be these
LONG delays that speak of?  (would be a great win for FreeBSD- "My
'time to login:' at most sites sucks, but the ones that use FreeBSD as
their server really jams!")  I'm sure that my site (cybernet.com) is
not the only one on the Internet w/o DNS reverse name entries.
(I'm currently getting on my ISP's case about getting reverse DNS
set up for us at their site- it's not that hard to set up secondary
name servers.)

Thanks for listening.  I hope that I've made myself clear.


-Mark Taylor
mtaylor@cybernet.com