312-50V11 · Question #62
You are the Network Admin, and you get a compliant that some of the websites are no longer accessible. You try to ping the servers and find them to be reachable. Then you type the IP address and…
The correct answer is A. Traffic is Blocked on UDP Port 53. DNS uses UDP port 53 to resolve hostnames to IP addresses; blocking this port prevents URL-based resolution while direct IP access still works because it bypasses DNS entirely.
Question
You are the Network Admin, and you get a compliant that some of the websites are no longer accessible. You try to ping the servers and find them to be reachable. Then you type the IP address and then you try on the browser, and find it to be accessible. But they are not accessible when you try using the URL. What may be the problem?
Options
- ATraffic is Blocked on UDP Port 53
- BTraffic is Blocked on UDP Port 80
- CTraffic is Blocked on UDP Port 54
- DTraffic is Blocked on UDP Port 80
How the community answered
(36 responses)- A92% (33)
- C6% (2)
- D3% (1)
Why each option
DNS uses UDP port 53 to resolve hostnames to IP addresses; blocking this port prevents URL-based resolution while direct IP access still works because it bypasses DNS entirely.
DNS queries are sent over UDP port 53 by default. When this port is blocked by a firewall or security policy, the browser cannot resolve a URL's hostname to an IP address, causing the site to appear inaccessible by name. Accessing the server by its IP address works because the browser skips the DNS resolution step entirely, confirming that DNS traffic - not the server itself - is the problem.
HTTP uses TCP port 80, not UDP port 80; blocking it would prevent browser access whether using a URL or a direct IP address, which contradicts the observed symptom.
UDP port 54 is not assigned to any standard protocol involved in web browsing or name resolution.
HTTP uses TCP port 80, not UDP port 80; this is the same incorrect choice as B and would not produce the selective URL-only failure described in the scenario.
Concept tested: DNS UDP port 53 and hostname resolution troubleshooting
Source: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
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