News Group Posts

slow ping times dns resolv.conf

From: Jeff Liebermann <jeffl@comix.santa-cruz.ca.us>
Subject: Re: terrible ping and DNS
Date: Thu, 20 Jun 2002 07:11:15 -0700
References: <l7u2husk77gkjcdgbr5fao4rfl1ggafos5@4ax.com> 

On Thu, 20 Jun 2002 09:58:39 +0200, Andrzej Pinczuk <andy@send.pl>
wrote:

>Hello
>
>I configured DNS server (sco 5.0.5). All fine works but...
>When I reboot server and I try ping from other hosts
>by IP (not by domain !) adress, it looks like:
>
>ttl=64 time=0
>ttl=64 time=3030
>ttl=64 time=6060
>ttl=64 time=9090 
>  (time is still increasing by value 3030)
>
>  etc., etc.
>
>Files resolv.conf contains:
>
>domain  .
>nameserver   10.9.0.11
>hostresorder  bind local
>
>More info:
>1. When line "hostresorder" no exists,
>ping by IP doesn't work !
>2. When I stop DNS server by  /etc/ndc stop
>ale is OK (problem appears when I reboot/turn off computer).
>
>Where is problem ?
>Andy

I just had the same problem in my office precipitated by replacing my
Linux based firewall, with a Watchguard SOHO router/firewall.

It took two cups of coffee to figure out what I broke.  What happened
is that I had the cacheing DNS server in the Linux firewall set as the
first DNS nameserver in my resolv.conf.  The Watchguard does NOT have
a DNS cache.  I guess(tm) it takes exactly one second for ping to
decide that the first nameserver is not returning anything useful and
go on to the 2nd nameserver line.  

One difference is that my delays were exactly 1 second instead of your
3 second delays.  My guess(tm) is that your OSR5 box is trying 3 times
before blundering onward, while my 3.2v4.2 box only tries once.

I don't understand why ping insists on doing a lookup on every packet,
even for ping by IP address.  My guess(tm) is that ping is doing a
reverse DNS lookup and that's failing.  I could dig out the sniffer
and be sure, but not this week.  Therefore my guess(tm) is that your
internal nameserver at 10.9.0.1 is having a bad day and is comatose.
See if temporarily replaceing that nameserver with a real outside DNS
server fixes the problem.

Incidentally, my resolv.conf resolution order looks like this:
   hostresorder  local bind
I had to put my internal hosts in /etc/hosts to prevent telnet and ftp
login delays caused by an unwanted server reverse DNS lookup.  With
the reversed order, I found that my system was doing numerous wasted
DNS lookups to the various outside nameservers before decideing to
lookup the name/ip in /etc/hosts.

Disclaimer:  There's an awful lot of guesswork in the above.

-- 
Jeff Liebermann  150 Felker St #D  Santa Cruz CA 95060
(831)421-6491 pgr (831)426-1240 fax (831)336-2558 home
http://www.LearnByDestroying.com   WB6SSY
jeffl@comix.santa-cruz.ca.us   jeffl@cruzio.com
 

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