Re: [CentOS] Help with iptables rule for blocking UDP port 53

Sean Carolan wrote:

I do have a rule for blocking TCP, forgot to mention that. You can see from my tcpdump output above that the inbound packet is UDP though. I wonder why iptables doesn't block it even with this rule?

Try to insert the rule (-I) instead of append (-A). I recall encountering weirdness between using the two different methods for adding a rule. I don't know why, but it seems to make a difference in some cases. The man page doesn't make it clear to me what the difference is and why it (might) cause a change of behavior.

I'm not an iptables expert, for my real firewalls I use OpenBSD.

nate