Re: Very slow DNS

From: Mark South (marksouth_at_null.invalid)
Date: 02/03/05 

Date: Thu, 03 Feb 2005 17:29:43 +0100

On Thu, 03 Feb 2005 16:43:45 +0100, Unforgiven wrote:

> Recently I've begun having problems with DNS being very slow under Linux, a
> DNS query could take up to 30 seconds. While Windows was unaffected, this
> problem was observed both under Fedora Core 3 and Knoppix 3.7.

Is this with IPv6 turned on or off? That 30 seconds delay seems VERY
familiar.

If it's IPv6, the problem is common with other distros, notably Mandrake
10.1

> Today I've been doing some digging using Ethereal, and it turns out that
> it's actually the DNS servers (or perhaps the network itself) at fault. They
> simply fail to respond to more than half the DNS queries. Under Windows,
> this problem is not as severe since it will retry a query every second if no
> response is received, and it will cache DNS records. Linux on the other hand
> only repeats the query about once every 5 seconds, which means if it fails
> twice, I have to wait 15 seconds. It also appears no or only limited caching
> is performed.

Is the half of the queries that are ignored made up of IPv6 packets, and
then they respond to the fallback IPv4 queries?

> So my question is: can I decrease the retry interval and/or set up a DNS
> cache?

Try turning off IPv6. It's worked like magic for a large number of us. 

-- 
Mark South: World Citizen, Net Denizen

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