News Group Posts

resolv.conf dns cache

From: Jeff Liebermann <jeffl@comix.santa-cruz.ca.us>
Newsgroups: comp.unix.sco.misc
Subject: Re: network configuration woes,gateway,DNS
Date: Tue, 13 Jun 2000 10:11:01 -0700
Message-ID: <i8pcksk88uk3qapeb9nci5j7r9lia6e49s@4ax.com> 
References: <8gvmgj$lhj$1@nnrp1.deja.com>
<5ep6js0jdqdangq11bkv1cg9f2gd3pgakb@4ax.com>
<20000530075956.I19369@jpradley.jpr.com>
<39463169.7115654@news.supernews.com>
<0gpaks0a5b1ktokjvs51cebgqro6dpavqo@4ax.com>
<4.3.2.7.2.20000612193600.00c76960@scogr1.cscc.maximus.com> 

On Mon, 12 Jun 2000 23:39:52 GMT, Ken Wolff <kenw@cscc.maximus.com>
wrote:

>We've got all internal IPs in /etc/hosts.  We also have 'hostresorder local 
>bind', but if our internet connection goes down, telnet/ftp/pop takes about 
>2 minutes to connect.  I just don't see where the hostresorder line is even 
>being looked at.  We're not running named on our OpenServer machine but are 
>running routed.  If what you say is suppose to work, what are we doing wrong?

To keep things exact, we are talking about running telnet/ftp/pop3
*FROM* an OSR5 box to somewhere else.  If this is in reference to
Windoze workstations, doing DNS lookups for netbios names, the
following discussion does *NOT* apply.  In these cases, the Windoze
workstations initiate their own DNS lookups.  Unfortunately, a variety
of bugs and registry tweaks seem to be required to stop these DNS
lookups.  (I have a list of MS Q numbers somewhere on the topic).  The
common practice is to block these Windoze initiated netbios lookups at
the firewall.

Now, back to OSR5.

Resolv.conf has one nasty habit.  You can horribly misconfigure it and
not one single program will ever complain.  It even says this in the
man pages.

Everything you've done is correct.  I don't know if routed has any
effect.  Probably not.  In theory, a telnet or ftp to a local machine
listed in /etc/hosts should NOT require a DNS lookup.  However, POP3
might require a reverse DNS lookup to authenticate the HELO line.
Checking.... yep.  If my domain does not agree with my connected IP,
Qpop claims I'm a charlatin.  POP3 is going to lookup the name.  Later
versions of Qpopper allow the reverse DNS feature to be disarmed.
        http://www.eudora.com/qpopper/

I can test if telnet and ftp initiate DNS lookups easily enough in my
office while sniffing the network.  I have a test setup that should
work.  However, I won't be there until Thurs or Fri.

Incidentally, the reason most systems use DNS caches is not to speed
up DNS lookups.  It's to reduce the tendency to bring up a dialup link
every time there's a DNS lookup.  In my case, if my full time
connection is dead, the DNS cache will return an almost immediate
"nothing found" allowing the application to continue instead of
waiting 3 minutes for a response.  [Insert plug for configurable
timeouts on everything].  The DNS servers return fast responses.  It's
the applications that are waiting around for 3 or more minutes for a
response.

-- 
Jeff Liebermann   jeffl@comix.santa-cruz.ca.us
150 Felker St #D  Santa Cruz CA  95060
831-421-6491 pager   831-429-1240 fax
http://www.cruzio.com/~jeffl/sco/   SCO stuff

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