ipv6 support makes ipv4 dns painfully slow

[Simon Morgan]

the default "alias net-pf-10 ipv6" line in /etc/modprobe.d/aliases is causing my
dns query times (in firefox at least) to slow to a crawl, changing it to "alias
net-pf-10 off" fixes the problem.

[Matt Zimmerman (mdz)]

Why does this cause DNS queries to be slow for some users? I have never
experienced this problem.

[Fabio Massimo Di Nitto (fabbione)]

It is simply because firefox is ipv6 aware (like all the mozilla-*).
If ipv6 is loaded firefox attempts to resolve/connect via ipv6 first.
The timeout is pretty high in mozilla itself. It is not a dns problem.

It can also be configured via /proc interface but i really don't suggest
that approach.

In any case this behaviour prefectly conforms to RFC. the bug is invalid tho.

Fabio

[Matt Zimmerman (mdz)]

But I assume that behaviour should hold for all Ubuntu systems. I have never
seen a delay because of this.

[Fabio Massimo Di Nitto (fabbione)]

It depends. If he has an unrouted ipv6 network over there it can take time because
there might be a real ipv6 address assigned but firefox (or whatever application)
will take longer to go in timeout.

Probably ( I am only assuming ) there is a radvd instance running on another machine
on the same network that is releasing real ipv6 addresses that are not routed.

Fabio

[Simon Morgan (sjmorgan)]

I'm pretty sure my ISP (BT Yahoo!) doesn't support IPv6 at all. If other people
aren't having problems with DNS being slow in firefox/mozilla then should I file
this as a bug in those programs? As I say disabling IPv6 fixed it completely.

[Matt Zimmerman (mdz)]

*** Bug 13577 has been marked as a duplicate of this bug. ***

[nd (ndd)]

I have the same problem, I dont see what harm can come of setting ipv6 in
firefox to true by default. For many ppl with this problem, who dont happen to
know if their dns is 4 or 6, it will be a major turnoff when running this
distribution. Epiphany is slow with this setting too, Ive tried it!

[Trevor Schauls (trevorschauls)]

A fix for me was to change the dns servers to 208.67.222.222 and 208.67.220.220 Maybe this should be the default dns servers in Ubuntu?

[James Michael DuPont (jamesmikedupont)]

I have this problem in 9.04, only on one computer.
Cannot get any high speed internet access.
Even wget is failing. Only google works.
Ifconfig shows lots of failures.

Attached are the log files that I could collect and my attempts at changing the etc files.
I also added the ipv6 flag to firefox

here are some excerpts :
logs.txt:/var/log/syslog:Jun 25 13:12:40 Denethor kernel: [ 38.473013] eth0: no IPv6 routers present

Here is the route :
route.txt:192.168.2.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0
route.txt:169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth0
route.txt:0.0.0.0 192.168.2.254 0.0.0.0 UG 0 0 0 eth0

I tried to turn ipv6 off.
modes.txt:/etc/modprobe.d/00local:alias ipv6 off
modes.txt:/etc/modprobe.d/blacklist.local:blacklist ipv6

eth0 Link encap:Ethernet HWaddr 00:18:f3:93:9f:f6
          inet addr:192.168.2.129 Bcast:192.168.2.255 Mask:255.255.255.0
          inet6 addr: fe80::218:f3ff:fe93:9ff6/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:1295 errors:80 dropped:0 overruns:0 frame:80
          TX packets:904 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:878148 (878.1 KB) TX bytes:185797 (185.7 KB)
          Interrupt:19 Base address:0xdead

thanks,
mike