Recently we upgraded our server at Host Europe to get better hardware and more RAM for less money/month. Moving from one server version to the next (v4 to v6 with us) means you get the new server for 7 days (and some more if you need the time and ask nicely) in parallel to the old. In this time you can setup the new system and move all data. After that time, the old server is shut down and away.
Since we were forced to re-setup the new system, I chose to switch the DNS server software: Goodbye bind, hello djbdns (more precisely: dbndns, Debian's djbdns fork with IPv6 support).
Denic, the registrar for .de domains, requires everyone to have at least two DNS servers. Hosteurope offers AutoDNS for that: Register your domain for AutoDNS, and you'll get one of their name servers assigned as secondary NS (I regularly have a1.rsns.hosteurope.de, c1.rsns.hosteurope.de and ns2.hans.hosteurope.de). They will update themselves automatically with AXFR zone transfers.
Failed zone transfers
This automatism was source of my problem: It did not work. The serial number on the secondary name server did not match the primary's even after a day:
$ dig +short @ns1.cweiske.de SOA cweiske.de ns1.cweiske.de. hostmaster.cweiske.de. 1359617938 16384 2048 1048576 2560 $ dig +short @c1.rsns.hosteurope.de SOA cweiske.de ns1.cweiske.de. hostmaster.cweiske.de. 1359488555 16384 2048 1048576 2560
I am using axfrdns now, and its log file /etc/axfrdns/axfrdns4/log/main/current only told me that the remote server aborted the connection:
tcpserver: status: 1/40 tcpserver: pid 22112 from 22.214.171.124 tcpserver: ok 22112 0:126.96.36.199:53 :188.8.131.52::45540 50ed8003001c00000000000000000000:b1e4:1583 0006 cweiske.de 50ed8003001c00000000000000000000:b1e4:1584 00fc cweiske.de axfrdns: fatal: unable to read from network: connection reset tcpserver: end 22112 status 28416
I had no idea what was going on and contacted the Host Europe support.
Finding the problem
The support answered some days later; they did investigate the issue and could not find a problem on their part. They provided an excerpt from their DNS server log file:
transfer of 'cweiske.de/IN' from 184.108.40.206#53: failed while receiving responses: bad label type end of transfer resetting failed while receiving responses: bad label type end of transfer
Because of this they suspected a problem on my side, which they underpinned with the output of a AXFR transfer test via dig:
$ dig -t AXFR cweiske.de @220.127.116.11 ; <<>> DiG 9.7.3 <<>> -t AXFR cweiske.de @18.104.22.168 ;; global options: +cmd cweiske.de.2560INSOAns1.cweiske.de. hostmaster.cweiske.de. 1359631614 16384 2048 1048576 2560 ... _xmpp-client._tcp.cweiske.de. 86400 INSRV0 0 5222 xmpp.cweiske.de. ;; Got bad packet: bad label type 75 bytes 89 f5 84 00 00 00 00 01 00 00 00 00 0c 5f 78 6d ............._xm 70 70 2d 73 65 72 76 65 72 04 5f 74 63 70 07 63 pp-server._tcp.c 77 65 69 73 6b 65 02 64 65 00 00 21 00 01 00 01 weiske.de..!.... 51 80 00 17 00 05 00 00 14 95 05 78 6d 70 70 07 Q..........xmpp. 63 77 65 69 73 6b 65 02 64 65 00 cweiske.de.
So the problem was the _xmpp-server._tcp.cweiske.de SRV record. Thanks to Florian Riehe for finding the issue.
Fixing the SRV record
The SRV line in my DNS data file looked like this:
Nice and readable, isn't it? In case you did not spot the totally obvious problem: The second \005 is wrong, it has to be a \004.
The reason for this cryptic line is that djbdns does not have built-in "nice" support for SRV records; you have to use its generic record syntax ("uncommon data lines") to express them. This is error prone as I had to experience.
Since I don't want to write those lines myself, I use a djbdns SRV record generator . Having to use it sucks, but what else can I do? D. J. Bernstein rejects the SRV patch because he thinks the generic record syntax suffices.
Nevertheless, AXFR zone transfers work now:
$ dig +short @c1.rsns.hosteurope.de SOA cweiske.de ns1.cweiske.de. hostmaster.cweiske.de. 1360100327 16384 2048 1048576 2560 $ dig +short @ns1.cweiske.de SOA cweiske.de ns1.cweiske.de. hostmaster.cweiske.de. 1360100327 16384 2048 1048576 2560