Computer Networking Basics
Which correctly describes the basic function of a (packet-filtering) firewall?
- AIt encrypts communication to prevent eavesdropping along the path
- BIt passes only permitted traffic and blocks the rest, according to rules based on source and destination IP addresses, port numbers and so on
- CIt distributes incoming packets among several servers to spread the processing load
Show answer and explanation
Answer: B. It passes only permitted traffic and blocks the rest, according to rules based on source and destination IP addresses, port numbers and so on
A firewall is placed, for example, at the boundary between an internal network and the internet, and allows or denies traffic according to predefined rules. A typical setting is "from outside, allow only traffic to port 443 of the public web server and deny all other incoming connections." Most firewalls today perform stateful inspection, keeping track of connection state and automatically letting through the return packets of connections started from inside. They do not encrypt, so they are combined with TLS or a VPN to protect traffic. They also cannot stop attacks that come through an allowed port (such as those exploiting web application vulnerabilities), so other measures such as a WAF are used as well.
- A. Encryption is the job of TLS or a VPN.
- B. Correct. It filters traffic by rules on addresses and port numbers.
- C. That is what a load balancer does.