Delayed DNS server response ...

Albretch Mueller · External Since: Jul 15, 2009 Posts: 9

Hi,
~
I have noticed a very delayed DNS server response (for about 15
seconds) even if I hit the same server so it makes my internet
connection very slow
~
I am using Linux/knoppix through a router and I have checked and
changed my router. What do you think could be causing this problem?
~
Thanks
lbrtchx

David Schwartz · External Since: Apr 29, 2007 Posts: 57

On Jul 15, 5:21 pm, Albretch Mueller <lbrt... DeleteThis @gmail.com> wrote:

> I have noticed a very delayed DNS server response (for about 15
> seconds) even if I hit the same server so it makes my internet
> connection very slow

When you do what? Test with 'nslookup'? Or use some kind of
application?

What is the exact command that replicates the problem?

> I am using Linux/knoppix through a router and I have checked and
> changed my router. What do you think could be causing this problem?

We'd have to guess without details. Are you hitting a local server
that you administer or a remote one? Are you having problems with
names that don't exist, names that do exist, all, only local names?
Remote ones?

Are you putting a '.' on the end of the name when you test? Or are you
making the system try different domain endings?

Have you looked to see what's going on during those 15 seconds?

DS

Albretch Mueller · External Since: Jul 15, 2009 Posts: 9

actually I am using wget like this:
~
knoppix@Knoppix:~/cmllpz/jobs/certs/comptia/RFID/Antennas/PIERB/12$
wget http://ceta.mit.edu/PIERB/pierb12/12.08122303.pdf
--21:33:51-- http://ceta.mit.edu/PIERB/pierb12/12.08122303.pdf
=> `12.08122303.pdf'
Resolving ceta.mit.edu... 18.62.7.143
Connecting to ceta.mit.edu|18.62.7.143|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 819,916 (801K) [application/pdf]

100%
[================================================================================>]
819,916 187.04K/s ETA 00:00

21:34:11 (183.68 KB/s) - `12.08122303.pdf' saved [819916/819916]

knoppix@Knoppix:~/cmllpz/jobs/certs/comptia/RFID/Antennas/PIERB/12$
wget http://ceta.mit.edu/PIERB/pierb12/13.08120503.pdf
--21:34:11-- http://ceta.mit.edu/PIERB/pierb12/13.08120503.pdf
=> `13.08120503.pdf'
Resolving ceta.mit.edu... 18.62.7.143
Connecting to ceta.mit.edu|18.62.7.143|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 466,194 (455K) [application/pdf]

100%
[================================================================================>]
466,194 182.12K/s

21:34:29 (181.52 KB/s) - `13.08120503.pdf' saved [466194/466194]
~
and I do notice a number of things that shouldn't be happening like a
constant delay of approx. 5 seconds if I use nslookup hitting a number
of different sites or the same site and 10 seconds if I simply ping
the same site
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
knoppix@Knoppix:~/tmp$ sh ./nslookup00.sh
Wed Jul 15 22:00:29 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.45.100
Name: google.com
Address: 74.125.67.100
Name: google.com
Address: 74.125.127.100

Wed Jul 15 22:00:34 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: youtube.com
Address: 208.65.153.238
Name: youtube.com
Address: 208.117.236.69

Wed Jul 15 22:00:39 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.de
Address: 72.14.221.104
Name: google.de
Address: 74.125.77.104
Name: google.de
Address: 216.239.59.104

Wed Jul 15 22:00:44 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.it
Address: 216.239.59.104
Name: google.it
Address: 72.14.221.104
Name: google.it
Address: 74.125.77.104

Wed Jul 15 22:00:49 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: facebook.com
Address: 69.63.184.142
Name: facebook.com
Address: 69.63.178.11
Name: facebook.com
Address: 69.63.176.140

Wed Jul 15 22:00:54 EDT 2009
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
knoppix@Knoppix:~/tmp$ sh ./nslookup02.sh
Wed Jul 15 22:06:33 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.45.100
Name: google.com
Address: 74.125.67.100
Name: google.com
Address: 74.125.127.100

Wed Jul 15 22:06:38 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.127.100
Name: google.com
Address: 74.125.45.100
Name: google.com
Address: 74.125.67.100

Wed Jul 15 22:06:43 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.67.100
Name: google.com
Address: 74.125.127.100
Name: google.com
Address: 74.125.45.100

Wed Jul 15 22:06:48 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.45.100
Name: google.com
Address: 74.125.67.100
Name: google.com
Address: 74.125.127.100

Wed Jul 15 22:06:54 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.127.100
Name: google.com
Address: 74.125.45.100
Name: google.com
Address: 74.125.67.100

Wed Jul 15 22:06:59 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.67.100
Name: google.com
Address: 74.125.127.100
Name: google.com
Address: 74.125.45.100

Wed Jul 15 22:07:04 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.45.100
Name: google.com
Address: 74.125.67.100
Name: google.com
Address: 74.125.127.100

Wed Jul 15 22:07:14 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.127.100
Name: google.com
Address: 74.125.45.100
Name: google.com
Address: 74.125.67.100

Wed Jul 15 22:07:19 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.67.100
Name: google.com
Address: 74.125.127.100
Name: google.com
Address: 74.125.45.100

Wed Jul 15 22:07:24 EDT 2009
Server: 192.168.0.1
Address: 192.168.0.1#53

Non-authoritative answer:
Name: google.com
Address: 74.125.45.100
Name: google.com
Address: 74.125.67.100
Name: google.com
Address: 74.125.127.100

Wed Jul 15 22:07:29 EDT 2009
knoppix@Knoppix:~/tmp$
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
knoppix@Knoppix:~/tmp$ sh ./nslookup04.sh
Wed Jul 15 22:14:01 EDT 2009
PING google.com (74.125.45.100) 56(84) bytes of data.
64 bytes from yx-in-f100.google.com (74.125.45.100): icmp_seq=1 ttl=53
time=54.9 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 54.954/54.954/54.954/0.000 ms
Wed Jul 15 22:14:06 EDT 2009
PING google.com (74.125.127.100) 56(84) bytes of data.
64 bytes from pz-in-f100.google.com (74.125.127.100): icmp_seq=1
ttl=52 time=122 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 122.044/122.044/122.044/0.000 ms
Wed Jul 15 22:14:17 EDT 2009
PING google.com (74.125.67.100) 56(84) bytes of data.
64 bytes from gw-in-f100.google.com (74.125.67.100): icmp_seq=1 ttl=53
time=51.4 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 51.431/51.431/51.431/0.000 ms
Wed Jul 15 22:14:27 EDT 2009
PING google.com (74.125.45.100) 56(84) bytes of data.
64 bytes from yx-in-f100.google.com (74.125.45.100): icmp_seq=1 ttl=53
time=51.2 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 51.266/51.266/51.266/0.000 ms
Wed Jul 15 22:14:37 EDT 2009
PING google.com (74.125.127.100) 56(84) bytes of data.
64 bytes from pz-in-f100.google.com (74.125.127.100): icmp_seq=1
ttl=52 time=130 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 130.722/130.722/130.722/0.000 ms
Wed Jul 15 22:14:47 EDT 2009
PING google.com (74.125.67.100) 56(84) bytes of data.
64 bytes from gw-in-f100.google.com (74.125.67.100): icmp_seq=1 ttl=53
time=51.4 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 51.491/51.491/51.491/0.000 ms
Wed Jul 15 22:14:57 EDT 2009
PING google.com (74.125.45.100) 56(84) bytes of data.
64 bytes from yx-in-f100.google.com (74.125.45.100): icmp_seq=1 ttl=53
time=51.5 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 51.531/51.531/51.531/0.000 ms
Wed Jul 15 22:15:08 EDT 2009
PING google.com (74.125.127.100) 56(84) bytes of data.
64 bytes from pz-in-f100.google.com (74.125.127.100): icmp_seq=1
ttl=52 time=122 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 122.113/122.113/122.113/0.000 ms
Wed Jul 15 22:15:18 EDT 2009
PING google.com (74.125.67.100) 56(84) bytes of data.
64 bytes from gw-in-f100.google.com (74.125.67.100): icmp_seq=1 ttl=53
time=54.9 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 54.993/54.993/54.993/0.000 ms
Wed Jul 15 22:15:28 EDT 2009
PING google.com (74.125.45.100) 56(84) bytes of data.
64 bytes from yx-in-f100.google.com (74.125.45.100): icmp_seq=1 ttl=53
time=54.9 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 54.962/54.962/54.962/0.000 ms
Wed Jul 15 22:15:38 EDT 2009
knoppix@Knoppix:~/tmp$

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Why is this happening?
~
lbrtchx

Maxwell Lol · External Since: Feb 11, 2009 Posts: 8

David Schwartz <davids.DeleteThis@webmaster.com> writes:

> Have you looked to see what's going on during those 15 seconds?

wireshark/tcpdump would be a great way to see what is going on.

Joe Beanfish · External Since: Apr 11, 2006 Posts: 105

Albretch Mueller wrote:
> Hi,
> ~
> I have noticed a very delayed DNS server response (for about 15
> seconds) even if I hit the same server so it makes my internet
> connection very slow
> ~
> I am using Linux/knoppix through a router and I have checked and
> changed my router. What do you think could be causing this problem?

Maybe you have multiple servers configured in resolv.conf and the
first one doesn't work.

Joe · External Since: Jul 16, 2009 Posts: 7

On 2009-07-16, Joe Beanfish <joe.DeleteThis@nospam.duh> wrote:
> Albretch Mueller wrote:
>> Hi,
>> ~
>> I have noticed a very delayed DNS server response (for about 15
>> seconds) even if I hit the same server so it makes my internet
>> connection very slow
>> ~
>> I am using Linux/knoppix through a router and I have checked and
>> changed my router. What do you think could be causing this problem?
>
> Maybe you have multiple servers configured in resolv.conf and the
> first one doesn't work.

It's also possible that your system is configured to use IPV6 and the
DNS server does not support it yet. This is becoming more rare, but
if it's the case, DNS lookups can be delayed until the IPV6 request
times out.

--
Joe - Linux User #449481/Ubuntu User #19733
joe at hits - buffalo dot com
"Hate is baggage, life is too short to go around pissed off all the
time..." - Danny, American History X

Pascal Hambourg · External Since: Oct 11, 2006 Posts: 186

Hello,

Joe a écrit :
>
> It's also possible that your system is configured to use IPV6 and the
> DNS server does not support it yet. This is becoming more rare, but
> if it's the case, DNS lookups can be delayed until the IPV6 request
> times out.

I don't think that ping would issue IPv6 queries for direct and reverse
resolutions.

Joe · External Since: Jul 16, 2009 Posts: 7

On 2009-07-16, Pascal Hambourg <boite-a-spam.RemoveThis@plouf.fr.eu.org> wrote:
> Hello,
>
> Joe a écrit :
>>
>> It's also possible that your system is configured to use IPV6 and the
>> DNS server does not support it yet. This is becoming more rare, but
>> if it's the case, DNS lookups can be delayed until the IPV6 request
>> times out.
>
> I don't think that ping would issue IPv6 queries for direct and reverse
> resolutions.

The DNS request goes out that way on some systems. I know it was a
serious problem when IPV6 was first introduced to Ubuntu, and occurred
in various other distros as well.

At this time, most DNS servers have been upgraded to at least deny the
IPV6 request immediately, but there are still some holdouts.

It couldn't hurt to blacklist ipv6 and remove the module, then try
again.

--
Joe - Linux User #449481/Ubuntu User #19733
joe at hits - buffalo dot com
"Hate is baggage, life is too short to go around pissed off all the
time..." - Danny, American History X

Greg Russell · External Since: Mar 10, 2009 Posts: 9

In news:h3o1l0$1eun$1@saria.nerim.net,
Pascal Hambourg <boite-a-spam DeleteThis @plouf.fr.eu.org> typed:

>> It's also possible that your system is configured to use IPV6 and the
>> DNS server does not support it yet. This is becoming more rare, but
>> if it's the case, DNS lookups can be delayed until the IPV6 request
>> times out.
>
> I don't think that ping would issue IPv6 queries for direct and
> reverse resolutions.

Isn't that the purpose of ping6 ?

Albretch Mueller · External Since: Jul 15, 2009 Posts: 9

OK when I try "ifconfig -a" I can see that it shows me two address an
inet and an inet6 one

But I am not sure which one is Linux networking internally using in
my case. How can I check that?

Also as you were telling me ping does not use IPV6 anyway and
something else that puzzles me is: Why are the DNS server responses
not cached? I usually go to a few places online, even if it takes so
long if it is only once it would be not fine, but much better

I don't have any servers running at this time. In fact I want to
troubleshoot this problem first

Thanks
lbrtchx

Greg Russell · External Since: Mar 10, 2009 Posts: 9

In news:83447e99-0f88-497f-9d51-f9c422a8a094@d32g2000yqh.googlegroups.com,
Albretch Mueller <lbrtchx.RemoveThis@gmail.com> typed:

> Also as you were telling me ping does not use IPV6 anyway and
> something else that puzzles me is: Why are the DNS server responses
> not cached?

/etc/init.d/nscd start

will start the name service cache daemon if you've installed it.

Joe · External Since: Jul 16, 2009 Posts: 7

On 2009-07-17, Albretch Mueller <lbrtchx.RemoveThis@gmail.com> wrote:
> OK when I try "ifconfig -a" I can see that it shows me two address an
> inet and an inet6 one

Right, so ipv6 is enabled.

>
> But I am not sure which one is Linux networking internally using in
> my case. How can I check that?

It is using both.

>
> Also as you were telling me ping does not use IPV6 anyway and
> something else that puzzles me is: Why are the DNS server responses
> not cached? I usually go to a few places online, even if it takes so
> long if it is only once it would be not fine, but much better

Ping isn't specifically using it, but the DNS lookup is. Also, unless
you have a caching DNS server in your LAN, you are probably not
caching DNS.

At the terminal prompt, try this:

ping www.google.com
modprobe -r ipv6
ping www.google.com

See if there is a significant time difference between the first and
second ping. If there is, add ipv6 to your modprobe blacklist, and
you should be all set for the time being. The ideal solution in this
case would be to get the ISP to upgrade their DNS servers...

>
> I don't have any servers running at this time. In fact I want to
> troubleshoot this problem first

Absolutely the best plan. Fix the problems you have before
introducing new ones... Wink

--
Joe - Linux User #449481/Ubuntu User #19733
joe at hits - buffalo dot com
"Hate is baggage, life is too short to go around pissed off all the
time..." - Danny, American History X

Pascal Hambourg · External Since: Oct 11, 2006 Posts: 186

Joe a écrit :
>>
>> Why are the DNS server responses not cached?

The standard libc resolver does not cache DNS replies. See nscd as
indicated by Greg. Some programs such as firefox have their own name cache.

>> Also as you were telling me ping does not use IPV6 anyway
>
> Ping isn't specifically using it, but the DNS lookup is.

In all my experience, the ping command included in GNU/Linux distros has
never used IPv6 DNS lookups even on IPv6-enabled systems (all mine are).
By "IPv6 DNS lookups" I mean AAAA queries for IPv6 address records, not
DNS queries over IPv6 when you have a DNS server listening on IPv6.
Besides, if you watch closely the result of Albrecht's ping test, you
will see that the delay in twice as in the nslookup test, meaning that
both direct (for the echo request) and reverse (for the echo reply) DNS
lookups are delayed. However a reverse lookup is just a standard PTR
query and has nothing to do with IPv6.

Anyway it's easy to settle : capture DNS traffic with tcpdump while
running ping and see whether there are IPv6 lookups.

Pascal Hambourg · External Since: Oct 11, 2006 Posts: 186

Greg Russell a écrit :
> Pascal Hambourg <boite-a-spam.TakeThisOut@plouf.fr.eu.org> typed:
>
>> I don't think that ping would issue IPv6 queries for direct and
>> reverse resolutions.
>
> Isn't that the purpose of ping6 ?

Yes. The only ping I know that does both IPv4 and IPv6 is the one
included in Windows Vista.

Albretch Mueller · External Since: Jul 15, 2009 Posts: 9

Joe I tried what you suggested to me and here are the results:
~
knoppix@Knoppix:~$ su -
root@Knoppix:~# whoami
root
root@Knoppix:~# ping www.google.com -c 4
PING www.l.google.com (74.125.67.106) 56(84) bytes of data.
64 bytes from gw-in-f106.google.com (74.125.67.106): icmp_seq=1 ttl=53
time=53.7 ms
64 bytes from gw-in-f106.google.com (74.125.67.106): icmp_seq=2 ttl=53
time=52.3 ms
64 bytes from gw-in-f106.google.com (74.125.67.106): icmp_seq=3 ttl=53
time=56.9 ms
64 bytes from gw-in-f106.google.com (74.125.67.106): icmp_seq=4 ttl=53
time=57.4 ms

--- www.l.google.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 15276ms
rtt min/avg/max/mdev = 52.380/55.152/57.475/2.146 ms
root@Knoppix:~# modprobe -r ipv6
FATAL: Module ipv6 is in use.
root@Knoppix:~# ping www.google.com -c 4
PING www.l.google.com (74.125.67.147) 56(84) bytes of data.
64 bytes from gw-in-f147.google.com (74.125.67.147): icmp_seq=1 ttl=53
time=52.2 ms
64 bytes from gw-in-f147.google.com (74.125.67.147): icmp_seq=2 ttl=53
time=52.0 ms
64 bytes from gw-in-f147.google.com (74.125.67.147): icmp_seq=3 ttl=53
time=51.1 ms
64 bytes from gw-in-f147.google.com (74.125.67.147): icmp_seq=4 ttl=53
time=53.0 ms

--- www.l.google.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 15269ms
rtt min/avg/max/mdev = 51.195/52.164/53.088/0.710 ms
root@Knoppix:~#
~
but I couldn't quite get what you meant by:
~
> See if there is a significant time difference between the first and
> second ping. If there is, add ipv6 to your modprobe blacklist, and
> you should be all set for the time being.
~
As you can see there is no difference whatsoever and ipv6 is in use
~
How can I disable it if it is causing the problem? I mean how exactly
do I tell Linux/knoppix to use ipv4 exclusively?
~
Also, let me better reword my question. Shouldn't DNS server
responses be cached on the router?
~
> Anyway it's easy to settle : capture DNS traffic with tcpdump while
> running ping and see whether there are IPv6 lookups.
~
OK, let me do that, run the same test and I will let you know what
the results were
~
Something I don't quite understand is why my ISP uses the same
address for both DNS servers and gateway. Could it be related to the
problem at hand? Also, the roter I am using right now has a feature
called "DYNAMIC DNS" should I enable it or do you think it all can be
narrowed down to the ipv4 vx ipv6 issue?
~
root@Knoppix:~# traceroute 66.114.74.45
traceroute to 66.114.74.45 (66.114.74.45), 30 hops max, 40 byte
packets
1 192.168.0.1 (192.168.0.1) 0.598 ms 0.404 ms 0.386 ms
2 CORE1-fhrp-n64-253.aceinnovative.com (66.114.64.253) 29.780 ms
32.260 ms 31.879 ms
3 rad1.aceinnovative.com (66.114.74.45) 32.880 ms 33.613 ms
34.535 ms
root@Knoppix:~# traceroute 66.114.74.195
traceroute to 66.114.74.195 (66.114.74.195), 30 hops max, 40 byte
packets
1 192.168.0.1 (192.168.0.1) 0.743 ms 0.608 ms 0.330 ms
2 CORE1-fhrp-n64-253.aceinnovative.com (66.114.64.253) 33.944 ms
31.800 ms 31.329 ms
3 ns2.aceinnovative.com (66.114.74.195) 33.158 ms 32.601 ms
31.748 ms
~
root@Knoppix:~# traceroute 66.114.70.1
traceroute to 66.114.70.1 (66.114.70.1), 30 hops max, 40 byte packets
1 192.168.0.1 (192.168.0.1) 0.594 ms 0.434 ms 0.413 ms
2 CORE1-fhrp-n64-253.aceinnovative.com (66.114.64.253) 32.794 ms
33.035 ms *
~
lbrtchx

Albretch Mueller · External Since: Jul 15, 2009 Posts: 9

~
Actually I just noticed that the primary DNS server was not properly
set. I find that very weird and I don't think that I wrongly entered
DNS addresses in various routers (I checked my written notes on actual
paper and my contract with the ISP)
~
But let me just take it in the easier/most plausible way, that I
myself made a mistake Wink

~
Thank you any way guys
lbrtchx

Joe · External Since: Jul 16, 2009 Posts: 7

On 2009-07-17, Albretch Mueller <lbrtchx DeleteThis @gmail.com> wrote:
> but I couldn't quite get what you meant by:
> ~
>> See if there is a significant time difference between the first and
>> second ping. If there is, add ipv6 to your modprobe blacklist, and
>> you should be all set for the time being.
> ~
> As you can see there is no difference whatsoever and ipv6 is in use
> ~
> How can I disable it if it is causing the problem? I mean how exactly
> do I tell Linux/knoppix to use ipv4 exclusively?

Is this a liveCD or an install? If it's installed, you'd add ipv6 to
the /etc/modprobe.d/blacklist file, then reboot. The other responses
here are indicating that it shouldn't make any difference at all,
though. It sure can't hurt to try it, but if it doesn't help, remove
the blacklist item, then reboot again...

> ~
> Also, let me better reword my question. Shouldn't DNS server
> responses be cached on the router?

Not if the router doesn't have a DNS cache. Many just forward the
requests on to the ISP's DNS server.

> ~
>> Anyway it's easy to settle : capture DNS traffic with tcpdump while
>> running ping and see whether there are IPv6 lookups.
> ~
> OK, let me do that, run the same test and I will let you know what
> the results were
> ~
> Something I don't quite understand is why my ISP uses the same
> address for both DNS servers and gateway. Could it be related to the
> problem at hand? Also, the roter I am using right now has a feature
> called "DYNAMIC DNS" should I enable it or do you think it all can be
> narrowed down to the ipv4 vx ipv6 issue?

Many companies use the same server for DNS and DHCP. And DDNS isn't
for the DNS server, but rather allows you to easily connect to your
machine from the outside world if you have a constantly changing IP.

--
Joe - Linux User #449481/Ubuntu User #19733
joe at hits - buffalo dot com
"Hate is baggage, life is too short to go around pissed off all the
time..." - Danny, American History X

Pascal Hambourg · External Since: Oct 11, 2006 Posts: 186

Albretch Mueller a écrit :
> root@Knoppix:~# modprobe -r ipv6
> FATAL: Module ipv6 is in use.

Once loaded, the ipv6 module cannot be unloaded (and one should not try
to unload it). As Joe said, you must prevent it from being loaded
(nice=blacklist, ugly=delete or rename file) and reboot.

> As you can see there is no difference whatsoever and ipv6 is in use

You didn't show the execution times, so we can see nothing. 'time' comes
in handy.

> Also, let me better reword my question. Shouldn't DNS server
> responses be cached on the router?

It depends on the router.

> Something I don't quite understand is why my ISP uses the same
> address for both DNS servers and gateway.

It's not your ISP, it's your router that performs both functions.

> Could it be related to the problem at hand?

Maybe the problem is in the router's DNS proxy, maybe it's beyond.

> Also, the router I am using right now has a feature
> called "DYNAMIC DNS"

This is unrelated to your issue.

Albretch Mueller · External Since: Jul 15, 2009 Posts: 9

~
Also, one of the confusing issues is that another person using
Windows XP and the same router I used didn't tell me about absolutely
any problems and he was using DHCP exactly as I was
~
Is it possible that Windows would detect that the primary DNS server
was wrongly set and accordingly changed to the secondary one?
~
lbrtchx

Bit Twister · External Since: Dec 19, 2004 Posts: 1894

On Sat, 18 Jul 2009 06:09:32 -0700 (PDT), Albretch Mueller wrote:
> Is it possible that Windows would detect that the primary DNS server
> was wrongly set and accordingly changed to the secondary one?

If both systems have setup the nic to use dynamic/dhcp then both
should get the same DNS values.

You would have to check the doze "ifconfig /all" output against your
settings to prove both of you are using the same values.

I use the same router but I have hard coded my DNS to OpenDNS servers
on my doze box even though it gets a dynamic ip addy.