[Techtalk] Slow DNS

[Noirin Plunkett]

Sounds like you may be (unwittingly) using IPv6 now - but the sites
you're trying to visit might not have AAAA records - so the machine is
spending time looking for one, then eventually giving up, and failing
over to IPv4...
You can disable IPv6 by adding the following line to
/etc/modprobe.conf:

alias net-pf-10 off

Once you've rebooted then, it should seem happier =)
Noirin

On Tue, 12 Oct 2004 01:44:05 +0100 (BST), David Sumbler
<david at aeolia.co.uk> wrote:
> Since I upgraded from Fedora Core 1 (with 2.4 kernel) to FC2 (with
> 2.6), I have noticed that often it takes a long time to resolve host
> names.  I haven't changed my /etc/resolv.conf file (which is correct)
> or anything like that.
> 
> It isn't associated with any particular program: for instance, Mozilla
> Firefox and Links both have the problem.
> 
> I just tried an experiment: I entered 'dig newswww.bbc.net.uk +trace'
> 
> and got the following output:
> 
> ; <<>> DiG 9.2.3 <<>> newswww.bbc.net.uk +trace
> ;; global options:  printcmd
> .                       165188  IN      NS      d.root-servers.net.
> .                       165188  IN      NS      e.root-servers.net.
> .                       165188  IN      NS      f.root-servers.net.
> .                       165188  IN      NS      g.root-servers.net.
> .                       165188  IN      NS      h.root-servers.net.
> .                       165188  IN      NS      i.root-servers.net.
> .                       165188  IN      NS      j.root-servers.net.
> .                       165188  IN      NS      k.root-servers.net.
> .                       165188  IN      NS      l.root-servers.net.
> .                       165188  IN      NS      m.root-servers.net.
> .                       165188  IN      NS      a.root-servers.net.
> .                       165188  IN      NS      b.root-servers.net.
> .                       165188  IN      NS      c.root-servers.net.
> ;; Received 436 bytes from 212.159.13.49#53(212.159.13.49) in 36 ms
> 
> uk.                     172800  IN      NS      NS1.NIC.uk.
> uk.                     172800  IN      NS      NS2.NIC.uk.
> uk.                     172800  IN      NS      NS4.NIC.uk.
> uk.                     172800  IN      NS      NS3.NIC.uk.
> uk.                     172800  IN      NS      NS5.NIC.uk.
> uk.                     172800  IN      NS      NSA.NIC.uk.
> uk.                     172800  IN      NS      NSB.NIC.uk.
> uk.                     172800  IN      NS      NS6.NIC.uk.
> uk.                     172800  IN      NS      NS7.NIC.uk.
> ;; Received 346 bytes from 128.8.10.90#53(d.root-servers.net) in 30144 ms
> 
> bbc.net.uk.             172800  IN      NS      ns0.thny.bbc.co.uk.
> bbc.net.uk.             172800  IN      NS      ns0.thdo.bbc.co.uk.
> ;; Received 89 bytes from 195.66.240.130#53(NS1.NIC.uk) in 30144 ms
> 
> newswww.bbc.net.uk.     300     IN      A       212.58.226.40
> ;; Received 52 bytes from 212.58.240.20#53(ns0.thny.bbc.co.uk) in 1 ms
> 
> I did this 4 times, within a few minutes, and got almost identical
> results each time.
> 
> Despite the times reported, only the first step took perhaps the time
> it says.  The 2nd an 3rd steps say that they took about 30 seconds
> each, but in fact it was about 45 seconds for each step, and the final
> step took not 1 millisecond, but about 30 seconds!
> 
> So where and why are these delays occurring?  Any ideas anybody?  My
> ISP assures me that they have no known problems relating to this.
> 
> David
> 
> --
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