Bind9 does not respond (only) over TCP

Question

The following dig command on the self server works fine . There is no firewall rule on the server related to this .

#dig @109.110.160.171 shabdiznet.com +tcp
;; communications error to 109.110.160.171#53: end of file

# netstat -lntu
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 0.0.0.0:53              0.0.0.0:*               LISTEN

The IP is public and yourself may test . The problem might not related to firewall because the ported is open from outside . The UDP works fine .

Answer 1

This server was upgraded from 12.04 and i don't know it was the problem or it is ubuntu 16.04 default behavior .

The problem was caused by dnsmasq . Actually the dnsmasq was listening on the port 53 .

/etc/default/dnsmasq

ENABLED=0

Then

service dnsmasq stop
service bind9 restart

Solved my problem .