Firewall A firewall is a network security system either hardware or software based,that uses rules to control incoming and outgoing network traffic.A firewall acts as a barrier between a trusted network and an untrusted network.

Types of Firewall:

a) Packet filtering firewall: This firewall works at network layer.As packets arrive they are filtered by their type,source and destination IP addresses and port information contained in each packet.Unknown traffic is only allowed up to level 3 of the network stack.

Advantages:

• Good performance
• Cost effective
• Transparent.

Disadvantage:

• Direct connection less
• Poor scalability.

b) Circuit level gateway firewall: It works at the session layer of OSI model and transport layer of TCP/IP model.It monitors handshakes between packets to determine whether a requested session is legitimate.

Advantages:

Provide service for many different protocol.

Disadvantage:

• Clients must be able to use them
• Can not inspect application layer

Limitations of firewall

1) Firewall can not protect against what has been authorised.

2) It can not stop social engineering attacks or an unauthorised user intentionally using their access for unwanted purposes.

3) It can not stop attacks if the traffic does not pass through it.

4) It is as effective as the rules that are configured to enforce.

Firewalls is excellent at enforcing corporate security policies.Majority of the firewalls can provide selective access via authentication functionality.Firewalls are singular in purpose and do not need to be made between security and usability.