Destination unreachable

**JKyleOKC** · May 9th, 2013

I'm continually getting error messages from my local DNS server, such as this small example:

Code:

May  8 10:43:54 mehitabel named[1086]: error (network unreachable) resolving 'sa.bbc.com/A/IN': 2001:503:231d::2:30#53
May  8 10:43:54 mehitabel named[1086]: error (network unreachable) resolving 'sa.bbc.com/A/IN': 2001:503:a83e::2:30#53
May  8 10:43:54 mehitabel named[1086]: error (network unreachable) resolving 'static.bbc.co.uk/A/IN': 2001:502:ad09::3#53
May  8 10:43:54 mehitabel named[1086]: error (network unreachable) resolving 'static.bbc.co.uk/A/IN': 2a01:40:1001:35::2#53
May  8 10:43:55 mehitabel named[1086]: error (network unreachable) resolving 'open.live.bbc.co.uk/A/IN': 2001:502:ad09::3#53
May  8 10:43:55 mehitabel named[1086]: error (network unreachable) resolving 'secure-us.imrworldwide.com/A/IN': 2001:503:231d::2:30#53
May  8 10:43:57 mehitabel named[1086]: success resolving 'secure-us.imrworldwide.com/A' (in 'imrworldwide.com'?) after reducing the advertised EDNS UDP packet size to 512 octets
May  8 10:43:57 mehitabel named[1086]: success resolving 'open.live.bbc.co.uk/A' (in 'bbc.co.uk'?) after reducing the advertised EDNS UDP packet size to 512 octets

However I've attempted to turn off EDNS in named.conf, and also to limit its packet size to 512 octets.

The strange thing I notice is that all of these messages deal with v6 addresses; they never show a v4 address. All of the threads I've found on Google indicate a firewall problem, but I have no v6 firewall configured... Any ideas to help me troubleshoot this? Could it be a problem at my ISP's servers, which I've configured as forwarders?

EDIT: Attempting to do "nslookup" on the addresses returns "Host unknown" from my ISP's server; AT&T apparently doesn't yet support DNS for v6!

**Warprunner** · May 9th, 2013

If you want to disable IPV6 I found this post for you...
http://ubuntuforums.org/showthread.p...ight=turn+ipv6

**JKyleOKC** · May 9th, 2013

Do you think that will work on Lucid? I noted that Karmic moved the support from a module into the kernel itself, so I apparently need a kernel parameter to turn it off. And I'll be moving to 12.04 soon since Lucid is about to go EOL...

**varunendra** · May 9th, 2013

Originally Posted by Warprunner

If you want to disable IPV6 I found this post for you...
http://ubuntuforums.org/showthread.p...ight=turn+ipv6

Wow! A post from 2005! Didn't read much after reading the date

As for current versions, this is how IPv6 is disabled permanently (of course can be reverted if required so) -
Add these lines to the /etc/sysctl.conf file :

# disable IPv6
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
net.ipv6.conf.lo.disable_ipv6=1

A single command to do this :

Code:

echo -e "\n# disable IPv6\nnet.ipv6.conf.all.disable_ipv6=1\nnet.ipv6.conf.default.disable_ipv6=1\nnet.ipv6.conf.lo.disable_ipv6=1" | sudo tee -a /etc/sysctl.conf

Additionally, set IPv6 "Method" to "Ignore" in Network Manager.
Hopefully this gets rid of the error messages.

PS:
Apparently, Lucid Desktop, along with Hardy Server, reached its EOL today : https://wiki.ubuntu.com/Releases
Although the repositories will stay there for a while before they'll be moved from archive.ubuntu.com to old-releases.ubuntu.com

**JKyleOKC** · May 10th, 2013

Many thanks! I've totally disabled Network Manager on this system, and use the interfaces file instead. I'll be staying with Lucid for a few more weeks, since I have some 300 GB of VMs on it that I'll need to back up for safety before starting to upgrade, and it'll then take me at least a week to get all my servers that run on the system (DNS, FTP, PostFix, and LAN router) back into action after making the change!