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Old 01-12-2006, 10:11 AM   #1
intargc
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Registered: Jan 2006
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Slow DNS Resolution


I've searched this forum as well as Google for DAYS. Actually, Month's... I'm at my wits end. I'm about to give up Slackware and switch to another distro... It's driving me insane. I can install any other distro on my laptop (I've tried Debian, Fedora and Gentoo) and they all seem to not have this problem! I've used Slackware since 7.0 and this problem started to arise in 9.1 for me. However, I just used a local DNS caching system and everything sped up tremendously. Well, now I can at home, but not at work due to firewall constraints...

DNS Resolution is SO slow sometimes. It takes anywhere from 30 to 45 seconds to resolve a name. This isn't just in Mozilla or any browser, but even when I ping or SSH to somewhere. My /etc/nsswitch.conf is correct as well as my /etc/resolv.conf. Same as they are when I had Fedora and Debian on this laptop, as a matter of fact.

Right now, I'm at work and I'm behind a firewall, of course. However, this didn't seem to bother Debian, Fedora, Gentoo or heck, even Windows XP! When I take my laptop home, I'm NOT behind a firewall and this same issue exists.

Right now I'm using Slackware 10.2 with kernel 2.6.14.3. Does anyone at all have any idea why DNS resolution is so slow in Slackware? This is my last chance at trying to figure this out before I just grin and bare it on learning a whole new distro and possibly facing the days of compile time using Gentoo again.
 
Old 01-12-2006, 12:56 PM   #2
Alien Bob
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Registered: Sep 2005
Location: Eindhoven, The Netherlands
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Perhaps you could start with posting the content of some of your configuration files?
To mind come the following;

/etc/resolv.conf
/etc/host.conf
/etc/nsswitch.conf
/etc/rc.d/rc.inet1.conf

Do you use a local caching DNS server? Then, also post:

/etc/named.conf
/var/named/caching-example/named.ca (I assume you're using this default file)

That last file could contain IP addresses for the root servers that are no longer in use, and if your own caching DNS server picks the wrong server for its query, it will find the door closed... to check out the list of current root servers, try running this command:
Code:
dig @a.root-servers.net . ns
and then compare the IP addresses of these current rootservers with the IP addresses of the rootservers in your local file (likely /var/named/caching-example/named.ca). You will probably notice that for some of the servers, the IP addresses has indeed changed over time.

Rather than using a caching DNS server that starts resolving process by querying one of the root servers (which can lead to long delays) it is often faster to rely on your local network or ISP's DNS server. If your computer uses DHCP to get an IP address, the DHCP server will also send the IP address(es) of nearby DNS servers, and this information is then written into /etc/resolv.conf.

Now, this is an answer that might not even apply to your problem (we'll see that when you post your config files) but I thought it would be good to show that relying on the Internet's root servers is not by definition a good idea (unless you keep your local list of root servers current... I do that by running this script as a cron job once a month).

Eric
 
  


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