[CentOS] Help with iptables rule for blocking UDP port 53
centos at linuxpowered.net
Tue Jul 15 18:43:45 UTC 2008
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.
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