Debian 6 Slow DNS Resolution

[KIA]

Hi,

DNS is slow to resolve under certain situations. A ping to a random domain will resolve almost instantly:

root@debian:~# time ping -c 1 bbc.co.uk
PING bbc.co.uk (212.58.224.138) 56(84) bytes of data.
64 bytes from virtual-vip.thdo.bbc.co.uk (212.58.224.138): icmp_req=1 ttl=122 time=31.8 ms

--- bbc.co.uk ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 31.805/31.805/31.805/0.000 ms

real    0m0.125s

It's a different story when it comes to wget against a fast HTTP server:

root@debian:~# time wget http://www.thinkbroadband.com/images/header/thinkbroadband-white.png
--2011-04-03 16:58:06--  http://www.thinkbroadband.com/images/header/thinkbroadband-white.png
Resolving www.thinkbroadband.com... 80.249.99.130, 2a02:68:1::4
Connecting to www.thinkbroadband.com|80.249.99.130|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 4015 (3.9K) [image/png]
Saving to: `thinkbroadband-white.png.1'

100%[======================================>] 4,015       --.-K/s   in 0.03s

2011-04-03 16:58:11 (124 KB/s) - `thinkbroadband-white.png.1' saved [4015/4015]


real    0m5.202s

I'm currently using Google DNS. The same issue occurs if I switch to OpenDNS.

Any ideas?

Cheers.

 

[eXor]

Looking at those timings, I'm not quite sure what the problem is.

real 0m5.202s vs real 0m0.125s ?

Isn't that the timing for the entire command, not just the DNS part?

Wget is doing a whole lot more than ping is doing, and pulling in many more bytes.

 

[KIA]

If you were to see a video of the wget command in action, you would see it sit on "resolving domain.com" for four seconds.

Here's the same command on another box:

[user@host /usr/home/user]$ time wget http://www.thinkbroadband.com/images/header/thinkbroadband-white.png
--2011-04-03 16:32:32--  http://www.thinkbroadband.com/images/header/thinkbroadband-white.png
Resolving www.thinkbroadband.com (www.thinkbroadband.com)... 80.249.99.130, 2a02:68:1::4
Connecting to www.thinkbroadband.com (www.thinkbroadband.com)|80.249.99.130|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 4015 (3.9K) [image/png]
Saving to: `thinkbroadband-white.png'

100%[======================================>] 4,015       --.-K/s   in 0.002s

2011-04-03 16:32:32 (2.49 MB/s) - `thinkbroadband-white.png' saved [4015/4015]


real    0m0.235s

 

[Subliminal Aura]

Output from these commands

cat /etc/resolv.conf

dig overclockers.co.uk @8.8.8.8

 

[KIA]

root@debian:~# cat /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4
root@debian:~#

root@debian:~# dig overclockers.co.uk @8.8.8.8

; <<>> DiG 9.7.2-P3 <<>> overclockers.co.uk @8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19790
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;overclockers.co.uk.            IN      A

;; ANSWER SECTION:
overclockers.co.uk.     9772    IN      A       91.151.218.10

;; Query time: 40 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Apr  3 19:50:45 2011
;; MSG SIZE  rcvd: 52

Similar to http://www.linuxquestions.org/questions/linux-networking-3/slow-dns-resolution-789109/

dig, host & ping don't suffer from the issue.

 

[Subliminal Aura]

dig, host & ping don't suffer from the issue.

Does it affect any other program other than wget ? Is web browsing ok ?

How about using curl instead

Tried this ?

http://www.mail-archive.com/[email protected]/msg00078.html

 

[KIA]

curl is just as slow as is ftp.

 

[Subliminal Aura]

curl is just as slow as is ftp.

Answer the question fully .... what about web browsing ?

 

[KIA]

Answer the question fully .... what about web browsing ?

It's a headless box. I'm not going to install a GUI.

 

[Subliminal Aura]

It's a headless box. I'm not going to install a GUI.

Don't need to install a GUI - anyway not to worry.

How about this

strace wget www.google.com

What does it hang on ?

 

[KIA]

I know of x11 forwarding etc. I don't want to install anything unnecessary if I can help it.

It hangs on:

recvfrom(3, "a`\201\200\0\1\0\3\0\0\0\0\3www\6google\3com\0\0\1\0\1"..., 2048, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("8.8.8.8")}, [16]) = 84
gettimeofday({1301858080, 376379}, NULL) = 0
poll([{fd=3, events=POLLIN}], 1, 4915

Let me know if you need the rest of the output.

 

[russ0r]

Post the output of

$ grep ipv6 /etc/modprobe.d/aliases

 

[KIA]

# alias net-pf-10 ipv6

 

[russ0r]

Edit that file and change the line to:

alias net-pf-10 off ipv6

Then reboot.

Not sure if it'll help but worth a shot.

 

[Subliminal Aura]

This is slowest terminal I've ever used.

You've tried as suggested above

wget -4 www.google.com

right ?

 

[KIA]

Edit that file and change the line to:

alias net-pf-10 off ipv6

Then reboot.

Not sure if it'll help but worth a shot.

Didn't help.

wget -4 www.google.com

right ?

Much quicker.

Sadly the issue still affects apt-get etc.

 

[Subliminal Aura]

Much quicker.

Thought you tried the link I posted earlier.

Please try to keep up when others are helping you out. So it is an ipv6 issue... Scroll up, there's enough in this thread for you to figure it out, without me spoon feeding the answer to you.

Follow @russ0r route

 

[KIA]

Thought you tried the link I posted earlier.

Please try to keep up when others are helping you out. So it is an ipv6 issue... Scroll up, there's enough in this thread for you to figure it out, without me spoon feeding the answer to you.

Oh dear, I missed something but I must have done it on purpose, right?

Forget the "help" if you're going to speak to me like that.

Thank you, russ0r, for the help without the unnecessary remarks.

 

[Subliminal Aura]

Oh dear, I missed something but I must have done it on purpose, right?

Forget the "help" if you're going to speak to me like that.

Thank you, russ0r, for the help without the unnecessary remarks.

LOL! Your post makes me feel a whole lot better ... thanks