I use the NETSTAT command frequently during my consulting assignments, however apart from the common options; I never delved into using all options of the command. My curiosity got the better of me and I went on to explore all the options of the NETSTAT command, so here goes

NETSTAT (network statistics) is a command-line utility that displays incoming & outgoing network connections, routing tables and various network interface statistics. The command has various parameters that can be used and is available on Unix, Linux and Windows based operating systems

Parameters of the netsat command on Windows based systems. Linux, Unix, BSD based systems have most of the parameters common with a few exceptions

A quick output of the help of the netstat command by appending /? gives us the following parameter options

A detailed explanation of each parameter with examples follows

-a   Displays all connections and listening ports

Running the netstat command with the -a parameter displays the of active connections as is displayed in the output below

C:\>netstat

Active Connections

  Proto  Local Address          Foreign Address              State
  TCP    host540:19208          microsoft.com:http    CLOSE_WAIT
  TCP    host540:19473          yahoo.com:http             ESTABLISHED

Starting with the protocol as the first column which could be either TCP/UDP based. The “host540:19208″ in the second column is a combination of the host name of the computer that the command is being run on which in this case is host540 and the local port number which is 19208. For well known services the protocol would be appended, for example host540:ntp but for services that are not well known the local port number would be mentioned

The foreign address is the website and the service that the connection was opened to which is microsoft.com:http in this case with port 80 (http) or web traffic and the connection state is CLOSE_WAIT

If the port is not yet established, the port number is shown as a * which would normally be seen in the output as “*:*”

-b   Displays the executable involved in creating each connection or listening port. In some cases well-known executables host multiple independent components, and in these cases the sequence of components involved in creating the connection or listening port is displayed.

C:\>netstat -b

Active Connections

Proto  Local Address          Foreign Address               State                        PID
  TCP    host540:19208       microsoft.com:http   CLOSE_WAIT       1148
  [iexplore.exe]

  TCP    host540:19473       yahoo.com:http             ESTABLISHED   7848
  [firefox.exe]

 

Additionally the process id of the process is also available. In this case the executable name is in [] at the bottom, on top is the component it called, and so forth until TCP/IP was reached. Note that this option can be time-consuming and will fail unless you have sufficient permissions

-e   Displays Ethernet statistics. This may be combined with the -s option
 

C:\>netstat -e
Interface Statistics

                                                    Received            Sent

Bytes                                              41185465        10381455
Unicast packets                      248414             246100
Non-unicast packets           48535               303
Discards                                        0                          0
Errors                                             0                          1
Unknown protocols             0

The number of packets, bytes, errors and other information received and sent is displayed. This may be useful when tracking network usage and can be combined with the -s option.  For example one may only want to see received packets of type http, which can be done using the -e and -s options

-n   Displays addresses and port numbers in numerical form

This is similar to the standard netstat option without any parameters, however dns queries are done to convert all addresses and port numbers into numerical form. For example, in the output microsoft.com would be listed as its corresponding ip address and http would be displayed as 80
 

-o   Displays the owning process ID associated with each connection

The process ID which owns the connection can be viewed and then other utilities like Sysinternals Process Explorer can be used to drill down and get further information. The process id is also displayed other options like -b as was mentioned above

-p proto   Shows connections for the protocol specified by proto; proto may be any of: TCP, UDP, TCPv6, or UDPv6.  If used with the -s option to display per-protocol statistics, proto may be any of IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP, or UDPv6

This is one of the most useful options to view specific connections opened by the protocol specified. For example, if one wants to view the opened UDP connections, the command netstat -p proto UDP could be used

-r   Displays the routing table

Here all interfaces present in the system with their netmask, gateway, metric and name of the ethernet adapter is displayed. It gives you  a quick overview of ip addresses assigned and interface name, etc. Active as well as persistent routes are displayed

-s   Displays per-protocol statistics.  By default, statistics are shown for IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP, and UDPv6; the -p option may be used to specify a subset of the default

Another useful option to view statistics per protocol. For example, to view only UDP statistics, the following command could be used

C:\>netstat -s -p UDP

UDP Statistics for IPv4

  Datagrams Received    = 328852
  No Ports              = 16880
  Receive Errors        = 79
  Datagrams Sent        = 197475

Active Connections

  Proto  Local Address          Foreign Address        State

  The output above does not have any active UDP connections

-v            When used in conjunction with -b, will display sequence of components involved in creating the connection or listening port for all executables.

After we have used the -b option to drill down and find out that a component [iexplore.exe] as well as other components were involved in creating the connection, we can further use the -v option to order the components involved in creating the connection. This is useful when understanding the sequencing of connection requests by an arbitrary application. It gives you an internal listing of .dll’s being called in real time

interval      Redisplays selected statistics, pausing interval seconds between each display.  Press CTRL+C to stop redisplaying statistics.  If omitted, netstat will print the current configuration information once

This is a good way to auto refresh the screen with any output desired. I might want to see the output of the netstat -n every 5 seconds. I would then use the netstat -n 5 command

To summarize, netstat is an external tool that is built into Windows, Unix, Linux, etc and displays a lot of useful information

I have been asked by many people of the best way to get your IP address. Here I demonstrate a few common methods to get your own IP address
 

IPCONFIG

By far the quickest and most common method of getting your IP address on Windows based systems is the ipconfig command which is typed at the command prompt.

The above image is the output of the command ipconfig with no arguments

IFCONFIG

To find out your IP address on a Linux / UNIX based system you need to use command ifconfig. If no arguments are given to ifconfig command it displays the status of the current active interfaces

The command syntax typed at the prompt is

$ /sbin/ifconfig

The output of above command displays Ethernet IP address, Mac address, subnet mask and other information
 

NETSTAT

NETSTAT is a command-line tool that displays network connections, routing tables, and a number of network interface statistics. It is available on Unix/Linux and Windows based operating systems.

The netstat command displays the IP address of the local system and connections

An important point to note is that initially the IP address 127.0.0.1 (localhost) is mentioned under the heading Local Address and when connections are opened to external address (during internet browsing, connecting to systems using protocols like FTP, etc) the actual local IP address of the system is displayed under the column Local Address

Programming Languages

Many programming languages like PHP, ASP, Java, etc have functions, methods to get the IP address of the local system

A sample script to get your IP address using Active Server Pages is mentioned below

<%
Response.Write “Hello! Your IP Address is: ” & Request.ServerVariables(“REMOTE_ADDR”)
%>

In the code abov, within the ASP tags, <% … %>, you can retrieve the IP address of a user through the ServerVariables collection of the Request object

Utilities

There are many utilities available on the internet that allow you to find your own IP address and more. Some of them are

IP Finder
IP Address Monster

Websites

Many websites allow you to find out your IP address and other information. A few of them are

http://whatismyipaddress.com
http://www.samspade.org
http://www.find-ip-address.org
http://www.ipaddresslocation.org