In this tutorial you’ll learn how to capture the LAN packets and use tools.
You’ll see the important function of a firewall in a security system.
No more words, let’s start:

Topology:  One Linux (backtrack4) and one Windows XP.

You’ll need: backtrack4 cd rom or pendrive, a windows machine, a network conection. Internet conection is a plus.

boot up the backtrack4 machine, use user:root password:toor. Type startx to up the X server, when KDE is loaded open a terminal.Follow the images:

1. # ifconfig eth0 up -> setting up your network interface
# dhclient3 eth0 -> taking a IP address using the DHCP Network Server ( in my LAN i have a DHCP Server if you dont have a DHCP server you can just take an IP to your interface using “ifconfig eth0 192.168.1.102″ for example )

2. Open the wireshark network tool

3.Select dont show again and click OK

4. Click in the show tthe capture options button:

5. Enable Display Options and Disable Name Resolution, click Start:

6. in the console, do a ping in your gateway:

PS: after 2 packets type ctrl+c to cancel the ping loop

7. wireshark: select the SECOND ARP PACKET, click in the mouse position ( see the image ) to go to step 8.

The next step I’ll show in the Part2.

You’ll able to edit the IPv4 Packet and manipulate the information in the hard way!