Firewall

Hey there,
Many of you heard about Firewall in the network. Here is something interesting to know about Firewall in Linux world.

In the linux, firewall is part of kernel (network arch). Firewall provides security by filtering the incoming, outgoing and forwarding packets. So you guys easily catch that it works on Network (IP) layer. Mostly firewall is designed in dedicated machine, where Admin can define firewall rules. In the early days of Linux the program that provide firewall was known as ipfwadm (IP Firewall for Admin). After 2.2 series there was another enhanced version of firewall called ipchains. It is called Ip chains because there are basically three ways a packet traverse.
1. It can go out from the NIC (Output)
2. Come in to NIC (Input)
3. It can be forward as per routing tables rules if it is not for the local machine (Forward)

In the Linux world this is known as a chain. Input chain, output chain and forward chain.
Though ipchain is good, in 2.4.X and later , the netfilter utilities get enhanced and the newer version came out called iptables. One can define firewall rules using iptable with a normal ease. iptables are extensible compare to ipchains and that’s the most important features available by iptables. NAT rules for forwarding can also be defined using iptables.

I will post how to define firewall rules using iptables once i will be done with it's implementation.

so enjoy!!!!!!!!!!!!!!!