How do I list all active network connections


To list all active network connections run "netstat -an" or "netstat -a".

        # netstat -a
        Active Internet Connections (including servers)
        Proto   Recv-Q   Send-Q Local Address         Foreign Address       (state)
        tcp          0        0 *,*                   *,*                   CLOSED     
        tcp          0        0 *,exec                *,*                   LISTEN     
        tcp          0        0 *,*                   *,*                   CLOSED     
        tcp          0        0 *,*                   *,*                   CLOSED     
        tcp          0        0 dole,login            norman-49,1016        ESTABLISHED
        tcp          0        0 dole,login            norman-49,1012        ESTABLISHED
        tcp          0        0 *,login               *,*                   LISTEN     
        tcp          0        0 *,shell               *,*                   LISTEN     
        ...
        udp          0        0 *,daytime             *,*
        udp          0        0 *,chargen             *,*
        udp          0        0 *,*                   *,*
        udp          0        0 *,49193               *,*

This shows there are 2 rlogin sessions from norman-49.

        # netstat -an
        Active Internet Connections (including servers)
        Proto   Recv-Q   Send-Q Local Address         Foreign Address       (state)
        tcp          0        0 *,*                   *,*                   CLOSED     
        tcp          0        0 *,512                 *,*                   LISTEN     
        tcp          0        0 *,*                   *,*                   CLOSED     
        tcp          0        0 *,*                   *,*                   CLOSED     
        tcp          0        0 129.134.49.23,513     129.134.49.17,1016    ESTABLISHED
        tcp          0        0 129.134.49.23,513     129.134.49.17,1012    ESTABLISHED
        tcp          0        0 *,513                 *,*                   LISTEN     
        tcp          0        0 *,514                 *,*                   LISTEN     
        tcp          0        0 *,515                 *,*                   LISTEN     
        ...
        udp          0        0 *,7                   *,*
        udp          0        0 *,42                  *,*
        udp          0        0 *,512                 *,*
        udp          0        0 *,517                 *,*
        udp          0        0 *,518                 *,*
        udp          0        0 *,37                  *,*
        udp          0        0 *,9                   *,*
        udp          0        0 *,13                  *,*
        udp          0        0 *,19                  *,*
        udp          0        0 *,*                   *,*
        udp          0        0 *,49193               *,*

Here are the same connections listed using "netstat -an".  The -n option
disables name lookup so the hostnames appear as IP addresses and the service
names appear as port numbers.  It is much quicker to run netstat -an because
netstat does not have to resolve all the names and services.

For more information see netstat(1), or services(4).