I have 3 nodes with virtually the same iptables rules loaded from a bash script, but one particular node is blocking traffic on port 53 despite listing it's accepting it:

$ iptables --list -v

Chain INPUT (policy DROP 8886 packets, 657K bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 ACCEPT     all  --  lo     any     anywhere             anywhere            
    2   122 ACCEPT     icmp --  any    any     anywhere             anywhere            icmp echo-request 
20738 5600K ACCEPT     all  --  any    any     anywhere             anywhere            state RELATED,ESTABLISHED 
    0     0 ACCEPT     tcp  --  eth1   any     anywhere             node1.com multiport dports http,smtp 
    0     0 ACCEPT     udp  --  eth1   any     anywhere             ns.node1.com udp dpt:domain 
    0     0 ACCEPT     tcp  --  eth1   any     anywhere             ns.node1.com tcp dpt:domain 
    0     0 ACCEPT     all  --  eth0   any     node2.backend        anywhere            
   21  1260 ACCEPT     all  --  eth0   any     node3.backend        anywhere            
    0     0 ACCEPT     all  --  eth0   any     node4.backend        anywhere            

Chain FORWARD (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 15804 packets, 26M bytes)
 pkts bytes target     prot opt in     out     source               destination

nmap -sV -p 53 ns.node1.com // From remote server

Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2011-02-24 11:44 EST
Interesting ports on ns.node1.com (1.2.3.4):
PORT   STATE    SERVICE VERSION
53/tcp filtered domain

Nmap finished: 1 IP address (1 host up) scanned in 0.336 seconds

Any ideas?

Thanks