A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. There are different types of firewalls including packet filters, application gateways, circuit-level gateways, and bastion hosts. A firewall inspects each packet of data and determines whether to allow it to pass through or block it from passing. Firewalls are used to prevent unauthorized access to private networks from the internet and can protect both individual computers and entire networks.

1. FIREWALL

8. Packet filter - It looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules . Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing . Packet Filtering Applications Presentations Sessions Transport DataLink Physical DataLink Physical Router Applications Presentations Sessions Transport DataLink Physical Network Network

9. Application gateway Application gateway (Proxy Server)- User uses TCP/IP applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation. Applications Presentations Sessions Transport DataLink Physical Network DataLink Physical Applications Presentations Sessions Transport DataLink Physical Application Gateway Applications Presentations Sessions Transport Network Network Telnet HTTP FTP

15. SECURED Firewall Thank You…… Source – >CNS Text Book (William Stallings) > Wikipedia