What Ports Are Open On My Router

What Ports Are Open On My Router?

Erick N. Borgard CCNP

Here is a little trick you can use to find out what ports are open on your Cisco router.  You can use the command show control-plane host open-ports command to see what ports your Cisco router is listening on for connections.  This command will also show if there are any connections presently established.

Internet_RTR#show control-plane host open-ports 

Active internet connections (servers and established)

Prot        Local Address      Foreign Address                  Service    State

 tcp                 *:23                  *:0                   Telnet   LISTEN

 tcp                 *:23    10.10.10.31:49664                   Telnet ESTABLIS

 udp                 *:67                  *:0            DHCPD Receive   LISTEN

 udp                 *:68                  *:0             BootP client   LISTEN

 udp                *:123                  *:0                      NTP   LISTEN

The above output shows the router is listening for connections for telnet, DHCP, BootP and NTP.  We can also see that the router has an established telnet connection from a device that sourced a connection from IP address 10.10.10.31 and a source port of 49664.  The connection was established to the router on the standard telnet port 23.  Using this command could help  to harden the router to prevent attacks.