DNS queries on Linux failing

I'm sure my config is correct....

[bluedalmatian]

I've got the IPs of my ISP's DNS servers in the file /etc/resolv.conf :

nameserver 158.43.240.4
nameserver 158.43.240.3

Then in the iptables config script I've got the following (& yes it does come after any drop all rules):

#allow outgoing DNS queries
/sbin/iptables -A OUTPUT -p udp --dport 53 -j ACCEPT

yet all DNS lookups fail giving an error such as "no servers could be reached"

I'd be grateful if anyone could give some indication as to why this is happening. I did wonder if it was a routing problem. The routing table only contains a default route, it won't accept the others for some reason, but I would have thought the default would would work for this even if its not the most efficient. Everythnig else works.

Thanks
AW

[bluedalmatian]

Fixed it! For the record iptables was only configured to allow established connections on the output chain, not the input one!

Thats the second error in O'Reilly's "Building Secure Servers with Linux"!