Check Network Connection Command

You need to use any one of the following tool or command under Linux to check network connections including their state, source/destination, and addresses and bandwidth usage etc..

1. ss command: It dump socket (network connection) statistics such as all TCP / UDP connections, established connection per protocol (e.g., display all established ssh connections), display all the tcp sockets in various state such as ESTABLISHED or FIN-WAIT-1 and so on.
2. netstat command: It can display network connections, routing tables, interfaces and much more
3. tcptrack and iftop commands: Displays information about TCP connections it sees on a network interface and display bandwidth usage on an interface by host respectively.

   Display Currently Established, Closed, Orphaned and Waiting TCP sockets, enter:

   # ss -s

   Sample outputs:

   Total: 529 (kernel 726)
   TCP:   1403 (estab 286, closed 1099, orphaned 1, synrecv 0, timewait 1098/0), ports 774
   
   Transport Total     IP        IPv6
   *   726       -         -
   RAW   0         0         0
   UDP   27        13        14
   TCP   304       298       6
   INET   331       311       20
   FRAG   0         0         0

   Or you can use the netstat command as follows:
   
   # netstat -s 

   Display All Open Network Ports

   Use the ss command as follows:
   # ss -l