Network Management (netstat)

netstat command (Network Statistics)
netstat displays the contents of various network-related data structures in depending on the options selected.

Syntax:
netstat < option/s >
multiple options can be given at one time.

-a  : displays the state of all sockets.

-r   : shows the system routing tables
-i   : gives statistics on a per-interface basis.
-m : displays information from the network memory buffers. On Solaris, this shows statistics for STREAMS
-p [proto] : retrieves statistics for the specified protocol
-s : shows per-protocol statistics. 

(some implementations allow -ss to remove fileds with a value of 0 (zero) from the display.)
-D : display the status of DHCP configured interfaces. 

-n : do not lookup hostnames, display only IP addresses.
-d (with -i) : displays dropped packets per interface.
-I [interface] retrieve information about only the specified interface.

-v : be verbose
interval :  number for continuous display of statictics.

$netstat -rn                       
Routing Table: IPv4                   
Destination    Gateway       Flags    Ref    Use    Interface
-------------------- -------------------- ----- ----- ------ ---------
192.168.1.0    192.168.1.11  U         1     1444    le0
224.0.0.0       192.168.1.11  U         1          0    le0
default          192.168.1.1    UG       1    68276   
127.0.0.1       127.0.0.1       UH       1    10497   lo0

This shows the output on a Solaris machine who's IP address is 192.168.1.11 with a default router at 192.168.1.1

Other important options with netstat: 

netstat -an | grep LISTEN | grep xxxx to grep for the port number
If you want to see what ports processes are listening on at a given moment and get a sorted list so you can see where there might be an available port, 

you can use the command below:
netstat -an | grep LISTEN | awk '{print substr($1,3)}' | sort –n

 
Netstat –anP tcp | grep ipaddress | wc –l  to grep the number of connections to the web server.