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

Sean Carolan wrote:

> What is confusing me is why my iptables rule is not working correctly.
>  TCPdump shows that the source is correct.  Any ideas?

try blocking tcp as well, most name servers listen on both tcp and
udp.

portal:~# netstat -anp | grep :53 | grep named
tcp        0      0 10.10.10.1:53           0.0.0.0:*               LISTEN  
  12978/named
tcp        0      0 127.0.0.1:53            0.0.0.0:*               LISTEN  
  12978/named
tcp        0      0 216.39.174.24:53        0.0.0.0:*               LISTEN  
  12976/named
udp        0      0 10.10.10.1:53           0.0.0.0:*                       
  12978/named
udp        0      0 127.0.0.1:53            0.0.0.0:*                       
  12978/named
udp        0      0 216.39.174.24:53        0.0.0.0:*                       
  12976/named



nate