Incomplete axfrdns response

djbdns

I'm trying to setup djbdns (tinydns, dnscache and axfrdns) in a private network. There is a secondary server running BIND that should be able to transfer the zone managed by tinydns (through axfrdns).

I get this error message in the axfrdns logs when I request a zone transfer:

axfrdns: fatal: unable to read data.cdb: format error

But in fact, the data.cdb file is the one used by tinydns, and it has been generated by tinydns-data: no visible problem with it.

If I do the transfer request manually with dig -t AXFR my_zone.com @172.16.2.200, I get a response, but only with the first ~20 entries from the data file (in the same order: SOA, NS, MX, A, ...), ended with the following message:

;; communications error to 172.16.2.200#53: end of file

Obviously, this is not the end of the file.

The full response (names have been slightly changed, for privacy purpose):

$ dig -t AXFR my_zone.com @172.16.2.200

; <<>> DiG 9.11.5-P4-5.1+deb10u2-Debian <<>> -t AXFR my_zone.com @172.16.2.200
;; global options: +cmd
my_zone.com.           2560    IN      SOA     srv-10.my_zone.com. hostmaster.my_zone.com. 1603886087 16384 2048 1048576 2560
my_zone.com.           259200  IN      NS      srv-10.my_zone.com.
srv-10.my_zone.com.    259200  IN      A       172.16.2.199
my_zone.com.           259200  IN      NS      vm01.my_zone.com.
vm01.my_zone.com.      259200  IN      A       172.16.2.201
my_zone.com.           259200  IN      NS      vm02.my_zone.com.
vm02.my_zone.com.      259200  IN      A       172.16.2.202
my_zone.com.           86400   IN      MX      0 my_zone.mail.protection.outlook.com.
aaa.my_zone.com.       86400   IN      A       78.40.125.202
bbb.my_zone.com.       86400   IN      A       193.186.8.180
ccc.my_zone.com.       86400   IN      A       78.40.125.106
ddd.my_zone.com.       86400   IN      A       78.40.125.202
eee.my_zone.com.       86400   IN      A       193.186.8.34
fff.my_zone.com.       86400   IN      A       35.204.32.245
ggg.my_zone.com.       86400   IN      A       192.168.10.81
hhh.my_zone.com.       86400   IN      A       13.69.156.71
iii.my_zone.com.       86400   IN      A       13.69.156.71
jjj.my_zone.com.       86400   IN      A       13.69.156.71
my_zone.com.           86400   IN      A       172.16.2.172
lll.my_zone.com.       86400   IN      A       172.16.2.186
mmm.my_zone.com.       86400   IN      A       172.16.2.187
nnn.my_zone.com.       86400   IN      A       172.16.2.170
ooo.my_zone.com.       86400   IN      A       172.16.2.171
;; communications error to 172.16.2.200#53: end of file

I tcpdumped the communication between the axfrdns client (172.16.2.170) and the server (172.16.2.200): I can't see a clear problem in it, except at some point, the server closes the connection (packet #22).

tcpdump

I thought it could be something in the data file, but switching the entries where it stops responding (in the above example, ooo.my_zone.com) and the one after (say ppp.my_zone.com) doesn't help. It now stops at ppp.my_zone.com (i.e. at the same position, not the same entry).

Each query response packet in the tcpdump contains multiple DNS response.

How can I transfer my whole zone (~340 entries) with axfrdns? Or how to debug further?

I had this mysterious problem too following an OS upgrade and recompile. Turns out I just had to increase the softlimit (from 300000 to 3000000) in /etc/axfrdns/run.

Incomplete axfrdns response

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