Sorry it’s because i do a lot of things in the same time: some in french and others in english…
So may be try to disable your firewall and then:
tcpdump -i eth0 udp port 53 -vv -X
Don’t forget to change eth0 by your network interface (you can get it with /sbin/ifconfig command)
On an other console try to make some dns resolve operations:
dig A test.com
Did you see some UDP packet going though eth0 when you run the command dig ?
And if you rerun the firewall ?
For the moment i don’t understand which iptables rules could block your dns it’s really strange for me.
Other idea: Have you upnp enable on your firewall, if yes disable it.