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View Full Version : [ubuntu] Very strange DNS name resolving problem

Jarre
July 3rd, 2008, 03:45 PM
First of all, if You're interested enough then scroll down to bottom of this post for the "not-so-important-background-information".

My problem seems to be some sort of "application layer name resolving problem". I can ping and connect (eg. using Firefox) to hosts using IP numbers, but all connection attempts using domain names end up with timeout.

Although ping and FF fail to resolve domain names, host and nslookup commands work just fine. And as I said, pinging hosts with IP numbers work.

At the moment I'm running Ubuntu 8.04 Desktop Live from CD.

EDIT: I've also tried installing Windows XP on the same computer and it works just fine, no problems at all.

My configuration with some comments:

ubuntu@ubuntu:~$ lspci | grep Ethernet
00:04.0 Ethernet controller: Silicon Integrated Systems [SiS] SiS900 PCI Fast Ethernet (rev 90)
00:09.0 Ethernet controller: 3Com Corporation 3c905B 100BaseTX [Cyclone] (rev 30)


I'm using SiS as eth0, I've also tried 3Com and that made no difference.

ubuntu@ubuntu:~$ ifconfig
eth0 Link encap:Ethernet HWaddr 00:0b:6a:b0:35:16
inet addr:192.168.0.108 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::20b:6aff:feb0:3516/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:189 errors:0 dropped:0 overruns:0 frame:0
TX packets:225 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:215034 (209.9 KB) TX bytes:33416 (32.6 KB)
Interrupt:16 Base address:0xd400

eth1 Link encap:Ethernet HWaddr 00:50:da:5c:12:eb
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:17 Base address:0xf80

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:7870 errors:0 dropped:0 overruns:0 frame:0
TX packets:7870 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:393500 (384.2 KB) TX bytes:393500 (384.2 KB)



At the moment eth0 is connected to a D-Link switch, where it gets the 192.168.x.x address. I've also tried connecting eth0 straight to cable modem's interface, but problems were exactly the same.

ubuntu@ubuntu:~$ more /etc/resolv.conf
### BEGIN INFO
#
# Modified_by: NetworkManager
# Process: /usr/bin/NetworkManager
# Process_id: 7804
#
### END INFO

search cable.inet.fi


nameserver 193.210.19.19
nameserver 192.168.0.1


ubuntu@ubuntu:~$ more /etc/nsswitch.conf
# /etc/nsswitch.conf
#
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed, try:
# `info libc "Name Service Switch"' for information about this file.

passwd: compat
group: compat
shadow: compat

hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4
networks: files

protocols: db files
services: db files
ethers: db files
rpc: db files

netgroup: nis
ubuntu@ubuntu:~$ more /etc/hosts
127.0.0.1 localhost
127.0.1.1 ubuntu

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts


And here are the results:

ubuntu@ubuntu:~$ host www.sonera.fi
www.sonera.fi has address 194.251.244.241
ubuntu@ubuntu:~$ nslookup www.sonera.fi
Server: 193.210.19.19
Address: 193.210.19.19#53

Non-authoritative answer:
Name: www.sonera.fi
Address: 194.251.244.241

ubuntu@ubuntu:~$ ping www.sonera.fi

ubuntu@ubuntu:~$


Above, I interrupted the ping command with CTRL-C after about five minutes.

And the background information:

I upgraded my cable modem internet connection and I had to get a new modem. Old one was Thomson TCW710 and the new one is Linksys (Cisco) WCM300-EU (don't know if this makes any difference).

After the upgrade my Ubuntu 7.10 server couldn't resolve any domain names. I'd been planning to upgrade to 8.04 and decided to do that, hoping that I could get rid of the problems.

Well, that didn't work. I can't install 8.04 server (or desktop) because the installer hangs at "Configuring APT - Scanning the mirror". Same thing with 7.10 and 7.04.
nixscripter
July 3rd, 2008, 04:26 PM
I don't know if this will help, but I looked up the /etc/resolv.conf man page, and the search keyword says this:


Search list for host-name lookup.

The search list is normally determined from the local domain name; by default, it contains only the local domain name. This may be changed by listing the desired domain search path following the search keyword with spaces or tabs separating the names.

...

Note that this process may be slow and will generate a lot of network traffic if the servers for the listed domains are not local, and that queries will time out if no server is available for one of the domains.


As an experiment, try removing the search line from your /etc/resolv.conf file, since you have an alternative nameserver (193.etc) to do resolutions.

Hope this helps.
Jarre
July 3rd, 2008, 04:39 PM
As an experiment, try removing the search line from your /etc/resolv.conf file, since you have an alternative nameserver (193.etc) to do resolutions.

Hope this helps.

Thanks for the advice, I tried to remove the "search" line from /etc/resolv.conf but that didn't help.
Jarre
July 3rd, 2008, 04:59 PM
Just to add some confusion :), I just booted my laptop with the same Ubuntu 8.04 desktop CD and everything works just fine; no problems with name resolving or anything. It's an IBM T41 with Intel chipset. So, what the h*ll is wrong with my server hardware? I don't want to install Windows on it, although it works...
nixscripter
July 3rd, 2008, 05:20 PM
When you do boot from CD then what does that resolv.conf file say?
Jarre
July 4th, 2008, 04:08 AM
When you do boot from CD then what does that resolv.conf file say?

After booting from CD:

ubuntu@ubuntu:~$ more /etc/resolv.conf
### BEGIN INFO
#
# Modified_by: NetworkManager
# Process: /usr/bin/NetworkManager
# Process_id: 7804
#
### END INFO

search cable.inet.fi


nameserver 193.210.19.19
nameserver 192.168.0.1
nixscripter
July 5th, 2008, 06:16 PM
Hmm, that looks okay.

What is your routing table (route command)? Is it the same on the CD versus the HD?

If that looks okay, I would then start seeing exactly what's being sent. Try the nslookup and the ping again with tcpdump running.
lswb
July 5th, 2008, 08:00 PM
If you have ever run ufw or any other firewall on the laptop, make sure that port 53 (I think, you can check /etc/services) isn't blocked.
Jarre
July 7th, 2008, 03:04 PM
Hmm, that looks okay.

What is your routing table (route command)? Is it the same on the CD versus the HD?

This is strange, route command does't finish at all, it hangs after link-local line:

ubuntu@ubuntu:~$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.0.0 * 255.255.255.0 U 0 0 0 eth0
link-local * 255.255.0.0 U 1000 0 0 eth0


So that's not okay at all.

If that looks okay, I would then start seeing exactly what's being sent. Try the nslookup and the ping again with tcpdump running.

tcpdump doesn't seem to work either. I started it with sudo tcpdump -vv and it doesn't output anything even if I'm performing ping, host and nslookup commands in another terminal window.
Jarre
July 7th, 2008, 03:05 PM
If you have ever run ufw or any other firewall on the laptop, make sure that port 53 (I think, you can check /etc/services) isn't blocked.

There's no firewall running at all, all ports are open.
nixscripter
July 8th, 2008, 11:49 AM
I don't see a default route in the routing table. Try adding one, and see if that works: sudo route add default eth0

Also, route sometimes takes a while. Try waiting like 5 minutes (for network timeouts or something), and then see if it finishes.
Jarre
August 15th, 2008, 02:54 PM
I added default route with

sudo route add default eth0

but that didn't seem to do anything. Route command stalls, I waited for like 15 minutes but nothing happened. And network isn't working at all, I get an IP address from ISP but that's it.
Jarre
October 18th, 2008, 04:00 PM
I added default route with

sudo route add default eth0

but that didn't seem to do anything. Route command stalls, I waited for like 15 minutes but nothing happened. And network isn't working at all, I get an IP address from ISP but that's it.

Well, I couldn't solve the original problem and bought a new hardware for my server which is working fine.