[ubuntu-us-mi] hostname lookup bug?

[Robert Citek]

I'm trying to figure out where the issue is with name resolution on
Ubuntu Lucid 10.04. Here are the symptoms in psuedo-commands:

on Red Hat machine:
$ dig @foo bar
-> 10.1.1.1

on Ubuntu:
$ dig @foo bar
-> 10.1.1.1

Remove bar from DNS on foo.

on Red Hat machine:
$ dig @foo bar
-> no IP

on Ubuntu:
$ dig @foo bar
-> 10.1.1.1

reboot Ubuntu machine.
on Ubuntu:
$ dig @foo bar
-> no IP

Why is Ubuntu still returning an IP for machine foo? What is being
cleared/stopped by the reboot?

I'll try to setup a self-contained real example a bit later.

Regards,
- Robert

[Wolfger]

My guess is: "Caching name servers store DNS query results for a
period of time determined in the configuration (time-to-live) of the
domain name record in question." (copied and pasted from
http://en.wikipedia.org/wiki/DNS_cache#Recursive_and_caching_name_server
because I couldn't remember the details off the top of my head)

Post by Robert Citek
I'm trying to figure out where the issue is with name resolution on
-> 10.1.1.1
-> 10.1.1.1
Remove bar from DNS on foo.
-> no IP
-> 10.1.1.1
reboot Ubuntu machine.
-> no IP
Why is Ubuntu still returning an IP for machine foo? ?What is being
cleared/stopped by the reboot?
I'll try to setup a self-contained real example a bit later.
Regards,
- Robert
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[Wolfger]

Possibly useful:
http://www.ubuntugeek.com/howto-clearflush-dns-cache-in-ubuntu.html

Post by Robert Citek
I'm trying to figure out where the issue is with name resolution on
-> 10.1.1.1
-> 10.1.1.1
Remove bar from DNS on foo.
-> no IP
-> 10.1.1.1
reboot Ubuntu machine.
-> no IP
Why is Ubuntu still returning an IP for machine foo? ?What is being
cleared/stopped by the reboot?
I'll try to setup a self-contained real example a bit later.
Regards,
- Robert
--
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[Robert Citek]

Thanks. That is useful to know. I checked my machine for nscd, but
alas, it is not running. In fact, it is not even installed.

But even if nscd was running, I find it disturbing that dig appears to
ignore that I explicitly specified the name server.

Regards,
- Robert

Post by Wolfger
http://www.ubuntugeek.com/howto-clearflush-dns-cache-in-ubuntu.html

Post by Robert Citek
I'm trying to figure out where the issue is with name resolution on
-> 10.1.1.1
-> 10.1.1.1
Remove bar from DNS on foo.
-> no IP
-> 10.1.1.1
reboot Ubuntu machine.
-> no IP
Why is Ubuntu still returning an IP for machine foo? ?What is being
cleared/stopped by the reboot?
I'll try to setup a self-contained real example a bit later.
Regards,
- Robert
--
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--
Wolfger
http://wolfger.wordpress.com/
The world is a mess, and I just... need to rule it.
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[Jay R. Wren]

I didn't reply to your message with any of the so far mentioned
suggestions BECAUSE dig talks directly to DNS servers, not to the local
resolver library.

I'm puzzled by the behavior you describe.
--
j

Post by Robert Citek
Thanks. That is useful to know. I checked my machine for nscd, but
alas, it is not running. In fact, it is not even installed.
But even if nscd was running, I find it disturbing that dig appears to
ignore that I explicitly specified the name server.
Regards,
- Robert

Post by Wolfger
http://www.ubuntugeek.com/howto-clearflush-dns-cache-in-ubuntu.html

Post by Robert Citek
I'm trying to figure out where the issue is with name resolution on
-> 10.1.1.1
-> 10.1.1.1
Remove bar from DNS on foo.
-> no IP
-> 10.1.1.1
reboot Ubuntu machine.
-> no IP
Why is Ubuntu still returning an IP for machine foo? What is being
cleared/stopped by the reboot?
I'll try to setup a self-contained real example a bit later.
Regards,
- Robert
--
ubuntu-us-mi mailing list
ubuntu-us-mi at lists.ubuntu.com
Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-us-mi

--
Wolfger
http://wolfger.wordpress.com/
The world is a mess, and I just... need to rule it.
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[David F]

Is "foo" a hostname or IP address? Are you sure that your query is going
where you think it is going? Are you sure that you successfully removed bar
from DNS on foo? Could you run "tshark -i <interface> udp and port 53"
(where <interface> is the name of the network interface through which
packets to foo are routed, e.g. eth0), then run the dig command, and post
the output? Obscure any sensitive information if you want, but be careful,
"pseudo-commands" sometimes hide a lot.

If you see no queries/replies, check carefully that you didn't make a
mistake with the sniffer command because as previously noted, dig should not
do local caching. Let's find out on which machine the problem is before
jumping to any conclusions.

-- David

Post by Robert Citek
I'm trying to figure out where the issue is with name resolution on
-> 10.1.1.1
-> 10.1.1.1
Remove bar from DNS on foo.
-> no IP
-> 10.1.1.1
reboot Ubuntu machine.
-> no IP
Why is Ubuntu still returning an IP for machine foo? What is being
cleared/stopped by the reboot?
I'll try to setup a self-contained real example a bit later.
Regards,
- Robert

[Robert Citek]

Post by David F
Is "foo" a hostname or IP address?

Foo is an IP address.

Post by David F
Are you sure that your query is going where you think it is going?

Prior to this experience, I would have said, yes. But now I'm not so sure.

Post by David F
Are you sure that you successfully removed bar from DNS on foo?

I'm pretty sure. The entry is not in the zone file and a dig on the
DNS machine itself does not return an answer for Bar but does for
other names. I get the same result using a RHEL machine and even the
Ubuntu machine. It just takes several minutes (or a reboot) on the
Ubuntu machine.

Post by David F
?Could you run "tshark -i <interface> udp and port 53"
(where <interface> is the name of the network interface through which
packets to foo are routed, e.g. eth0), then run the dig command, and post
the output? ?Obscure any sensitive information if you want, but be careful,
"pseudo-commands" sometimes hide a lot.

Will do.

Regards,
- Robert