A network technician has configured a new firewall to allow TCP port 80 traffic and deny UDP traffic. Users have reported that they are unable to access Internet websites. The technician verifies by…

The correct answer is D. UDP port 53 needs to be allowed. DNS (Domain Name System) resolves human-readable domain names (e.g., www.example.com) to IP addresses. DNS primarily uses UDP port 53 for queries. Because the firewall is blocking all UDP traffic, DNS queries cannot reach DNS servers, meaning domain names cannot be resolved…

Network troubleshooting

Question

A network technician has configured a new firewall to allow TCP port 80 traffic and deny UDP traffic. Users have reported that they are unable to access Internet websites. The technician verifies by attempting to access a popular website. Which of the following will MOST likely correct the error?

Options

AHTTP uses UDP
BDNS port 23 needs to be allowed
CHTTP needs port 443 allowed
DUDP port 53 needs to be allowed

How the community answered

(56 responses)

A
11% (6)
B
4% (2)
C
5% (3)
D
80% (45)

Explanation

DNS (Domain Name System) resolves human-readable domain names (e.g., www.example.com) to IP addresses. DNS primarily uses UDP port 53 for queries. Because the firewall is blocking all UDP traffic, DNS queries cannot reach DNS servers, meaning domain names cannot be resolved. Even though TCP port 80 (HTTP) is allowed, the browser cannot connect to any website by name without DNS resolution first. Allowing UDP port 53 restores DNS functionality and allows users to access websites. HTTP does not use UDP, port 23 is Telnet (not DNS), and port 443 is HTTPS not HTTP.

Topics

#DNS#UDP port 53#firewall rules#name resolution

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