iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
I use a router and have 53 tcp/udp routed to this computer.
ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:E0:18
2:B1:3C
inet addr:192.168.10.12 Bcast:192.168.10.255 Mask:255.255.255.0
inet6 addr: fe80::2e0:18ff:fed2:b13c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:107270 errors:0 dropped:0 overruns:0 frame:0
TX packets:204597 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:25480329 (24.2 MiB) TX bytes:40084259 (38.2 MiB)
Interrupt:177
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:162 errors:0 dropped:0 overruns:0 frame:0
TX packets:162 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:15542 (15.1 KiB) TX bytes:15542 (15.1 KiB)
sit0 Link encap:IPv6-in-IPv4
NOARP MTU:1480 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 3719/mysqld
tcp 0 0 0.0.0.0:81 0.0.0.0:* LISTEN 4041/ispconfig_http
tcp 0 0 192.168.10.12:53 0.0.0.0:* LISTEN 13885/named
tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 13885/named
tcp 0 0 0.0.0.0:21 0.0.0.0:* LISTEN 4291/proftpd: (acce
tcp 0 0 127.0.0.1:953 0.0.0.0:* LISTEN 13885/named
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 4234/master
tcp6 0 0 :::993 :::* LISTEN 3593/couriertcpd
tcp6 0 0 :::995 :::* LISTEN 3628/couriertcpd
tcp6 0 0 :::110 :::* LISTEN 3608/couriertcpd
tcp6 0 0 :::143 :::* LISTEN 3568/couriertcpd
tcp6 0 0 :::80 :::* LISTEN 4142/apache2
tcp6 0 0 :::22 :::* LISTEN 3882/sshd
tcp6 0 0 ::1:953 :::* LISTEN 13885/named
tcp6 0 0 :::25 :::* LISTEN 4234/master
tcp6 0 0 :::443 :::* LISTEN 4142/apache2
tcp6 0 432 ::ffff:192.168.10.12:22 ::ffff:192.168.10.243:48343 ESTABLISHED14259/0
udp 0 0 0.0.0.0:53 0.0.0.0:* 13885/named
udp 0 0 192.168.10.12:53 0.0.0.0:* 13885/named
udp 0 0 127.0.0.1:53 0.0.0.0:* 13885/named
udp6 0 0 :::32787 :::* 13885/named
I also rechecked with ISPs NOC and they state the port is not blocked.