Red Hat Bugzilla – Bug 507470
"Name or service not known" errors with Fedora 11 DNS server
Last modified: 2013-04-30 19:43:43 EDT
After upgrading our forwarding DNS server to Fedora 11, we started getting a lot of name lookup failures. At the time of a failure, there seem to be a lot of error messages of this form:
Jun 22 15:29:37 guru named: chase DS servers resolving 'mcnabbs.org/DS/IN': 126.96.36.199#53
Jun 22 15:29:37 guru named: not insecure resolving 'org/NS/IN': 188.8.131.52#53
Jun 22 15:29:37 guru named: not insecure resolving 'mcnabbs.org/A/IN': 184.108.40.206#53
The clients worked fine just a few days ago with a Fedora 10 DNS server with the same configuration.
Is there any information I can provide that would be helpful?
There have also been errors of the following form in the logs:
Jun 22 15:29:00 guru named: network unreachable resolving 'mcnabbs.org/DS/IN': 2001:500:f::1#53
Jun 22 15:29:00 guru named: network unreachable resolving 'mcnabbs.org/DS/IN': 2001:500:40::1#53
One last type of message I'm seeing a lot of is:
Jun 22 17:40:59 guru named: success resolving 'mail.mcnabbs.org/A' (in 'mcnabbs.org'?) after reducing the advertised EDNS UDP packet size to 512 octets
Jun 22 17:40:59 guru named: success resolving 'mail.mcnabbs.org/AAAA' (in 'mcnabbs.org'?) after reducing the advertised EDNS UDP packet size to 512 octets
I also noticed that after adding -4 to the options for named, name resolution seems to be working.
DNSSEC validation has been enabled by default in F11 and it might cause that lookups take more time. Would it be possible to try set `DNSSEC=off` in /etc/sysconfig/dnssec and check if it "solves" the problem, please?
Also please try this: run `dig @<your_server_ip> <name_which_often_fails> +dnssec` and check how long query takes in both cases - enabled and disabled DNSSEC validation. Make sure you run `rndc flush` command right before dig command to flush server's cache.
Since IPv6 is disabled, I'll have to reenable it to recreate the problem. I should be able to get to this tomorrow, but I'll need to warn a few users.
I don't see a problem on the mcnabbs.org domain. It resolves fine with DNSSEC and DLV enabled for me.
Oh, also make sure you have tcp port 53 open and not firewalled. DNSSEC can cause replies to require TCP uinstead of UDP.
There is a firewall upstream of the DNS server, but it is set to allow all outgoing connections and any established inbound connections through. Are any unusual firewall settings necessary for DNSSSEC?
Adam, I tried enabling/disabling dnssec and restarting the name server. With dnssec enabled, dig reported the query time as 4956 ms. With dnssec disabled, the query time was 1060 ms. I tried restarting a number of times (to clear the cache), and the results seemed pretty consistent: about 1 second without dnssec, and 5 to 6 seconds with dnssec.
Since comment #8, I've run this more times, and the times are actually pretty inconsistent. I even had one as long as 14 seconds (this one with DNSSEC disabled).
Make sure your firewall allows for DNS packets of larger size (say 4096) than most default (512). DNSSEC increases packet size, many firewalls will block these UDP packets, cause delay, and force failing back to TCP.
Jason, sorry for taking so long to respond to this. There are unfortunately several firewalls between the DNS server and the outside world. Do you happen to know whether iptables limits DNS packet size by default? I've tried googling for information and haven't found anything useful. If I'm sure it's not the iptables firewall, then I can report the packet loss further up the chain. Thanks for your help.
I don't believe iptables has a default limit for packet size. But Cisco's default and other protocol-inspecting firewalls often limit to 512.
Here is a resource to test your firewall to see what size it is allowing:
Thank you very much for that tip. It looks like we have a campus-wide firewall that's dropping packets, so I'll see if we can get them to fix it. In the meantime, I think I'll try setting edns-udp-size as a workaround.
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