What is the basic job of a firewall placed between a trusted internal network and the Internet?

Monitor traffic and allow or block it according to security rules

Encrypt every packet that leaves the internal network

Assign IP addresses to internal hosts

Speed up Internet access by caching all pages

A packet-filtering firewall decides to forward or drop a packet by examining which information?

The packet header: source/destination IP, port and protocol

The application data inside the packet, such as the email text

The history of all earlier packets in the session

How does a stateful inspection firewall improve on a simple packet filter?

It tracks connection state and allows only packets that belong to an established session

It works only at the application layer

It checks only the source IP address

It removes viruses from the data

Why is an application-level gateway (proxy firewall) slower but more thorough than a packet filter?

It makes the request on the client's behalf and examines the content of HTTP, FTP or mail traffic

Year not given

Firewall and its types

Short answer

A firewall filters traffic between trusted and untrusted networks based on security rules. Types: packet-filtering (checks headers), stateful inspection (tracks sessions), application gateway (proxy, layer 7), circuit-level, and personal firewall. They cannot prevent insider attacks or viruses in allowed traffic.

What is a firewall? Explain its types.

A firewall is a hardware or software system placed between a trusted internal network and an untrusted external network (such as the Internet) that monitors and filters all traffic according to a set of security rules, allowing authorised traffic and blocking the rest.

 Internet --> [ FIREWALL ] --> Internal network
              permit / deny

Types

Packet-filtering firewall: works at the network/transport layer. It checks each packet's header (source/destination IP, port, protocol) against rules and drops or forwards it. Fast and simple, but cannot examine the data and is weak against spoofing.
Stateful inspection firewall: also remembers the state of connections (e.g. TCP handshake) and allows only packets that belong to an established session. More secure.
Application-level gateway (proxy firewall): works at application layer; the client connects to the proxy, which makes the request for it. It can examine the content (HTTP, FTP, mail), but is slower.
Circuit-level gateway: checks TCP handshakes to see that a session is legitimate, without looking at the data.
Personal (host-based) firewall: software on a single computer.
Next-generation firewall (NGFW): combines the above with intrusion prevention and deep packet inspection.

Type	Layer	Strength	Weakness
Packet filter	3–4	Fast, cheap	No content checking
Stateful	3–4	Tracks connections	More memory
Application proxy	7	Deep checking	Slower

Limitations: it cannot stop insider attacks or viruses carried in allowed traffic.

✓ Answer checked by Claude Opus 5.5 (high effort)

All Operating System chapter 8 questions →