A firewall is a component or set of components that restricts access between a protected network and other sets of networks and are often used to protect an organisation’s networks from the Internet. a. Briefly describe the operational characteristics of: • a simple packet filter; • a stateful packet filter; • an application gateway; • a circuit level gateway.

a. Operational characteristics of:

• A simple packet filter: This type of firewall operates at the network level of the OSI model, or the IP layer of TCP/IP. It is designed to control access to a network by analyzing the incoming and outgoing packets and letting them pass or halt based on the source and destination IP addresses, port number, protocol, or other specific characteristics. However, it does not check the packet content, so it cannot prevent attacks that exploit application-specific vulnerabilities or functions.

• A stateful packet filter: This type of firewall, also known as a dynamic packet filter, keeps track of the state of network connections, such as TCP streams or UDP communication, traveling across it. It operates at the network layer but can also operate at the transport layer. When a packet is received, the firewall checks the packet's information against a table of existing connections. If the packet matches an existing connection, it's allowed to pass, otherwise it's denied.

• An application gateway: Also known as an application-level gateway, this type of firewall operates at the application layer of the OSI model. It inspects the content of traffic, monitoring application protocol and providing a complete, detailed view of what's happening in the network. It can block specific content, messages or commands that are known to be harmful, and it can also hide the details of the internal network by modifying traffic data.

• A circuit level gateway: This type of firewall operates at the session layer of the OSI model. It sets up two-way, "circuit" connections for traffic and once the connection is established, packets can flow between the hosts without further checking. It does not inspect the packet content, providing more efficiency but less security than an application gateway. It's typically used for "trusted" connections that do not require application-level filtering.