Firewall

Firewall is a system that helps in controlling unauthorized intrusion to a system in a network. It is a first step in protecting the private information of a network. Firewall implements the security by scanning each and every message coming to or going from the network. It blocks the messages that causes suspicion and do not meet the security requirements. It can be implemented on the hardware as well as the software.

A combination of the following techniques is used to implement the firewall:

• Packet filter: Packet filtering is a technique of cross-checking each and every “packet” passing through the network. They work at low level of the TCP/IP protocol stack. The packet which does not meet the standards as defined by the user is rejected. The whole process from the connection to transferring of data undergoes the following process:

1. Session request
2. Handshaking
3. Data transfer
4. Closing the connection

• Circuit-level gateway: This security system is implemented on the establishment of a connection of a TCP (Transfer control protocol) or UDP (User datagram protocol). On the establishment of the connection, packets can flow without any checking as it is a reliable connection. TCP and UDP are considered to be very reliable protocols.

• Application gateway: FTP and Telnet servers use the application gateway mechanism. The firewall works at the application layer of the TCP/IP protocol stack. Application layer interfaces with the user mode applications. This is a very effective way to implement the firewall as it is able to understand few applications and protocols. It also detects if any unwanted protocol is sneaking into the network via a non-standard port.

Proxy Server: It is used to hide the true network address to avoid any unwanted access to someone outside the network. Each and every message transmitted is intercepted in order to cause any security breach.

A private network is more prone to security threats from the internet. Firewall serves as a reliable security feature. For greater security, it is advised to encrypt the data. But, a proper implementation of the firewall requires a proper understanding of the networking concepts.