[Techtalk] Slow DNS

[David Sumbler]

On Tue, 12 Oct 2004, Noirin Plunkett wrote:

> 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 =)

Oh - the plot thickens!  Thanks for the suggestion: I have made the
alteration you suggest.  It does seem to have improved things just a
little.  Now when I issue the same 'dig' command as before, I get:

; <<>> DiG 9.2.3 <<>> newswww.bbc.net.uk +trace
;; global options:  printcmd
.                       136237  IN      NS      c.root-servers.net.
.                       136237  IN      NS      d.root-servers.net.
.                       136237  IN      NS      e.root-servers.net.
.                       136237  IN      NS      f.root-servers.net.
.                       136237  IN      NS      g.root-servers.net.
.                       136237  IN      NS      h.root-servers.net.
.                       136237  IN      NS      i.root-servers.net.
.                       136237  IN      NS      j.root-servers.net.
.                       136237  IN      NS      k.root-servers.net.
.                       136237  IN      NS      l.root-servers.net.
.                       136237  IN      NS      m.root-servers.net.
.                       136237  IN      NS      a.root-servers.net.
.                       136237  IN      NS      b.root-servers.net.
;; Received 436 bytes from 212.159.13.49#53(212.159.13.49) in 33 ms

uk.                     172800  IN      NS      NS1.NIC.uk.
uk.                     172800  IN      NS      NS2.NIC.uk.
uk.                     172800  IN      NS      NS3.NIC.uk.
uk.                     172800  IN      NS      NS4.NIC.uk.
uk.                     172800  IN      NS      NS5.NIC.uk.
uk.                     172800  IN      NS      NS6.NIC.uk.
uk.                     172800  IN      NS      NS7.NIC.uk.
uk.                     172800  IN      NS      NSA.NIC.uk.
uk.                     172800  IN      NS      NSB.NIC.uk.
;; Received 346 bytes from 192.33.4.12#53(c.root-servers.net) in 10065 ms

bbc.net.uk.             172800  IN      NS      ns0.thdo.bbc.co.uk.
bbc.net.uk.             172800  IN      NS      ns0.thny.bbc.co.uk.
;; Received 89 bytes from 195.66.240.130#53(NS1.NIC.uk) in 10050 ms

newswww.bbc.net.uk.     300     IN      A       212.58.226.30
;; Received 52 bytes from 212.58.224.20#53(ns0.thdo.bbc.co.uk) in 2 ms

and the four steps are consistently taking about 1, 15, 15 and 10
seconds respectively.  Over all, 3 times as fast as before, but still
not very satisfactory!  Any other ideas?

David

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