_really_ slow dns resolving

Rellig · n00b Joined: 25 Feb 2006 Posts: 46

hi,
dns resolving on the linux hosts in my network is really slow. i have no problems when using a windows pc, so i think it may be the router which sends somehow bad dns information.
do you have any idea about that and maybe know how to fix it without buing new hardware?

msalerno · Posted: Tue Dec 15, 2009 4:35 pm Post subject:

Check your DNS server, are both systems using the same servers?

By default windows caches DNS queries, which would make it look as if Windows was much faster.
Do the same nslookup from your windows system and your linux system, and before you do it on the windows system, do an ipconfig /flushdns

Rellig · n00b Joined: 25 Feb 2006 Posts: 46

every pc in the network uses my router dns-server.

i already did this and it's really like that, that windows is much faster in resloving dns names.

wrc1944 · Posted: Tue Dec 15, 2009 5:27 pm Post subject:

Don't know what "really slow" means in your case as it's a subjective description, but NOT disabling ipv6 on the local browser and machine can cause that- sometimes very perceptible.

In my case having ipv6 enabled made for very noticable slow web site accessing (dns lookup).

Edit: Other thoughts: Is your router and/or ISP even ipv6 capable, or does windows have ipv6 disabled?
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Rellig · n00b Joined: 25 Feb 2006 Posts: 46

dns lookups take up to 10 seconds.

everything here is ipv4

i did not disable ipv6 in windows and i don't know if it is turned on or not.

how can i disable ipv6 on gentoo?

msalerno · Posted: Tue Dec 15, 2009 7:54 pm Post subject:

It's a kernel config option. Here is some stuff that you need to answer.

1. When did this start happening? Has this always been the case?
2. What was the last thing to change?
3. How up to date is your gentoo install?
4. Are both systems connected the same way? (wireless or wired)
5. Are there any errors on your interface?
6. Is your router blocking any kind of traffic?
7. Did you try changing the DNS server on the linux server to a public DNS server other than your router? Was it faster?
8. On the linux host, is there a difference between dns queries via TCP or UDP (man dig)

That's all I can think of for now, I'm sure there are more questions, but you need to provide more details.

Rellig · n00b Joined: 25 Feb 2006 Posts: 46

1. i noticed it about 6 months ago, but i always had trubles using konqueror, but it had worked elsewhere
2. ?
3. up to date ~amd64
4. they are all connected via the same wired switch
5. everything works fine (except dns)
6. it is running a firewall (i never really cared about it in detail)
7. i just tried the google dns server (8.8.8.8) without any success, which is somehow surprising for me at the moment ...
8. i don't see a difference between tcp or udp - but i never got a time higher than 150ms

i have to add that if i'm not at home (as one gentoo host is my notebook) everything works fine ...

edit: i just installed dnsmasq. not the proper solution but better than nothing ...

wrc1944 · Posted: Tue Dec 15, 2009 9:51 pm Post subject:

Rellig,
In /etc/modprobe.d/aliases.conf, uncomment it in this section, like this

gajop · n00b Joined: 14 Oct 2009 Posts: 21

i'm having some trouble with DNS, but i think it's my IPS specific, switching to OPENDNS seems to makes things better