[Techtalk] Slow DNS
plunkett at gmail.com
Tue Oct 12 08:14:01 EST 2004
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
alias net-pf-10 off
Once you've rebooted then, it should seem happier =)
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 22.214.171.124#53(126.96.36.199) 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 188.8.131.52#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 184.108.40.206#53(NS1.NIC.uk) in 30144 ms
> newswww.bbc.net.uk. 300 IN A 220.127.116.11
> ;; Received 52 bytes from 18.104.22.168#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.
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