Firewall rule: allow or deny by port

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Which firewall rule lets secure web traffic (HTTPS) come into a school web server?

A allow inbound TCP 443

B deny inbound TCP 443

2. A firewall rule has three parts. Which list names them correctly?

A Action, direction, port

B Username, password, port

3. Which rule blocks Telnet (port 23) traffic coming in from the internet?

A allow inbound TCP 23

B deny inbound TCP 23

4. What does 'inbound' mean in a firewall rule?

A Traffic coming into the network from outside

B Traffic leaving the network to the internet

5. Which rule lets students on the school network visit websites over HTTPS?

A deny outbound TCP 443

B allow outbound TCP 443

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1allow inbound TCP 443		ALet incoming HTTPS web traffic through the firewall on port 443
2deny inbound TCP 23		Ballow outbound TCP 443
3A rule that lets your computer send web requests out to the internet over HTTPS		Cdeny inbound TCP 21
4Closing an unused port by blocking incoming traffic to it, such as port 21 for FTP that nobody uses		DThe rule has no port number, so it does not say which port to close. It should be something like deny inbound TCP 23.
5allow TCP 443		EBlock incoming Telnet connections on port 23
6deny inbound TCP		FThe rule has no direction. A firewall rule must say inbound or outbound so it is clear which way the traffic travels. It should be allow inbound TCP 443.

Definitions

allow inbound TCP 443

Fill in the Blanks

Complete each line of code by filling in the missing parts.

_____ inbound TCP 443

allow _______ TCP 443

____ inbound TCP 23

allow outbound TCP ___

deny inbound TCP __

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A # Web server firewall rules

B allow inbound TCP 80

C deny inbound TCP 443

D deny inbound TCP 23

Question 2

A # Block Telnet from outside

B allow inbound TCP 23

C allow inbound TCP 443

Question 3

A default allow inbound

B allow inbound TCP 443

C allow inbound TCP 80

Question 4

A # Staff PC: browse the web

B allow outbound TCP 443

C allow outbound TCP 80

D deny outbound 23 TCP

Question 5

A web: allow inbound TCP 23

B telnet: deny inbound TCP 23

C ftp: deny inbound TCP 21

Answer Key

Firewall rule: allow or deny by port

Section A: Quick Questions

A — allow inbound TCP 443

A — Action, direction, port

B — deny inbound TCP 23

A — Traffic coming into the network from outside

B — allow outbound TCP 443

Section B: Match the Pairs

allow inbound TCP 443 → Let incoming HTTPS web traffic through the firewall on port 443

deny inbound TCP 23 → Block incoming Telnet connections on port 23

A rule that lets your computer send web requests out to the internet over HTTPS → allow outbound TCP 443

Closing an unused port by blocking incoming traffic to it, such as port 21 for FTP that nobody uses → deny inbound TCP 21

allow TCP 443 → The rule has no direction. A firewall rule must say inbound or outbound so it is clear which way the traffic travels. It should be allow inbound TCP 443.

deny inbound TCP → The rule has no port number, so it does not say which port to close. It should be something like deny inbound TCP 23.

Section C: Definitions

allow inbound TCP 443 — A firewall rule with an action (allow), a direction (inbound) and a port (TCP 443). It lets incoming web traffic through. A deny rule on a port, such as 23, blocks it.

Section D: Fill in the Blanks

allow inbound TCP 443

deny inbound TCP 23

allow outbound TCP 443

deny inbound TCP 23

Section E: Spot the Error

C — A web server must accept HTTPS traffic. Port 443 should be allowed, so the line should be allow inbound TCP 443. Denying it would block every secure visitor.

B — The comment says Telnet (port 23) must be blocked. The action should be deny, so the line should be deny inbound TCP 23. Allowing it leaves an insecure port open.

A — A default of allow would leave every unused port open. The first line should be default deny inbound, so only the ports with allow rules can be used.

D — A rule is written in the order action, direction, protocol, then port number. The line should be deny outbound TCP 23, with the protocol before the port.

A — Web traffic over HTTPS uses port 443, not 23 (which is Telnet). The line should be web: allow inbound TCP 443.