Here you are the first post from the Useful command series.

Have you ever wonder how to figure out under what ports your router is listening, just take a look (try also nice command like show ip sockets detail)

R1#show control-plane host open-ports
Active internet connections (servers and established)
Prot Local Address Foreign Address Service State
tcp *:22 *:0 SSH-Server LISTEN
tcp *:23 *:0 Telnet LISTEN
tcp *:80 *:0 HTTP CORE LISTEN
tcp *:443 *:0 HTTP CORE LISTEN
tcp *:22 10.0.12.2:59470 SSH-Server ESTABLIS
udp *:67 *:0 DHCPD Receive LISTEN
udp *:56186 *:0 IP SNMP LISTEN
udp *:161 *:0 IP SNMP LISTEN
udp *:162 *:0 IP SNMP LISTEN