Help needed: DNS slow in Ubuntu 9.04

Wcool

Hi all,

For some reason DNS lookup on my Ubuntu 9.04 desktop is slow.
The rest of my computers (Windows and another Ubuntu computer) connected to the same router, be it wifi or CAT, are all fast.

These are the symptons: whenever I open a page in Firefox or Opera, the message "Looking up ... " appears, often more than 10 seconds, transfer after that seems normal. A second lookup on the same domain is slightly faster but still slow.

nslookup and dig is fast though.

I did some research but even after following most of the tips
(disable ipv6? editting all sorts of files, including network manager config) i am still lost.

Some quick questions:
1) how am i sure ipv6 is disabled?
If I type ifconfig -a, i still see a ip6 address out there?
2) some tips suggest I should edit /etc/modprobe.d/aliases
But I don't have that file! what is going on?
3) Is there a tool that can show me how an address is resolved?

Happy to post any conf file here if anyone would like to help.

Thanks a lot in advance.

bushy...

Run Wireshark on it and see what its actually doing , you'll see the DNS stuff a mile off

Wcool

Thanks Bushy,

After installing Wireshark I had a peek but at the same time DNS became fast again. I had made changes to my config files after reading some Ubuntu forums (especially resolv.conf) but didn't notice any difference in speed. Maybe it took installing Wireshark to refresh the DNS cache.

It seems to be working fast again now, so maybe the changes worked but just needed a reset. Thanks a lot, Wireshark is a very cool tool!

An Fear Aniar

Try Open DNS, if you're not already using it:

https://www.opendns.com/start/ubuntu.php


I've been looking at some threads on this and it seems the fixes you mentioned don't work in Jaunty because ipv6 is built into the kernel rather than being a module you can blacklist.

In Firefox you can disable ipv6 by typing about:config into the address bar, type in ipv6 and change the default to "true".

Hope this helps. They were talking about some fixes for jaunty but I tried some of the easy ones and they didn't work for me.

http://www.uluga.ubuntuforums.org/showthread.php?p=7268348

Hope this helps.
.

Wcool

An Fear Aniar wrote: »

Try Open DNS, if you're not already using it:

https://www.opendns.com/start/ubuntu.php


I've been looking at some threads on this and it seems the fixes you mentioned don't work in Jaunty because ipv6 is built into the kernel rather than being a module you can blacklist.

In Firefox you can disable ipv6 by typing about:config into the address bar, type in ipv6 and change the default to "true".

Hope this helps. They were talking about some fixes for jaunty but I tried some of the easy ones and they didn't work for me.

http://www.uluga.ubuntuforums.org/showthread.php?p=7268348

Hope this helps.
.

Thanks a lot! I am not a big fan of OpenDNS, I use Level 5 (4.2.2.1 - 4.2.2.6) Actually I also disabled the ipv6 setting in Firefox and noticed no difference, that's why I downloaded Opera to get see if that was the problem (but Opera had the same problem)

BUT: I followed the instructions in your first link (OpenDNS) but changed DNS to Level 5 and DID NOT REBOOT -> still having the same problem
The reboot solved it as in the instructions

I think this solved my problem! Thanks!

bushy...

Forgot to answer this bit

Wcool wrote: »

1) how am i sure ipv6 is disabled?

cat /proc/sys/net/ipv6/conf/all/disable_ipv6

to kill it

echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6

An Fear Aniar

bushy... wrote: »

Forgot to answer this bit



cat /proc/sys/net/ipv6/conf/all/disable_ipv6

to kill it

echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6

I tried that, as sudo su but when I rebooted it went back to status 0 again.

Bit puzzled.

I also tried the other one, adding

ipv6.disable=1

to the kernel boot line in /boot/grub/menu.lst but it didn't recognise the command.

.

Wcool

I think you can make those types of settings permanent by adding them to /etc/sysctl.conf


For instance:

net.ipv4.conf.all.log_martians = 1

equals:

echo 1 > /proc/sys/net/ipv4/conf/all/log_martians

bushy...

An Fear Aniar wrote: »

I tried that, as sudo su but when I rebooted it went back to status 0 again.

Bit puzzled.

.

Sorry ,was early when i posted , it will go back to whatever it "should" be at when you reboot.

Good few other things in there you can poke at

echo 1 > /proc/sys/net/ipv4/ip_forward

will enable routing between interfaces

Capt'n Midnight

opendns.org is handy alright,
use nslookup to check dns at command line

Probably not related to this problem, more for others later on, FireFox uses it's own DNS cache. https://addons.mozilla.org/ga-IE/firefox/addon/5914

An Fear Aniar

Capt'n Midnight wrote: »

Probably not related to this problem, more for others later on, FireFox uses it's own DNS cache. https://addons.mozilla.org/ga-IE/firefox/addon/5914

How does this work? Does the cache build up the more you use it? Does Firefox look in here first before asking a nameserver to rsolve the name?

.