You are the Network Admin, and you get a complaint 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…

Question

Options

• ATraffic is Blocked on UDP Port 53
• BTraffic is Blocked on TCP Port 80
• CTraffic is Blocked on TCP Port 54
• DTraffic is Blocked on UDP Port 80

• A
  73% (30)
• B
  2% (1)
• C
  17% (7)
• D
  7% (3)

Explanation

DNS Resolution Failure - UDP Port 53

When websites are reachable by IP address but not by URL (domain name), the issue lies with DNS (Domain Name System) - the service responsible for translating human-readable URLs into IP addresses. DNS primarily uses UDP Port 53 for standard queries, so if traffic is blocked on that port, DNS lookups fail, making URLs inaccessible even though the servers themselves are online.

Why the distractors are wrong:

• B (TCP Port 80): This is the standard HTTP port; if it were blocked, the website would fail even when accessed by IP address - but the scenario confirms IP access works fine.
• C (TCP Port 54): This port has no standard, widely recognized service role and is simply a fabricated distractor.
• D (UDP Port 80): HTTP runs on TCP, not UDP - Port 80 on UDP is not a valid standard service.

Memory Tip: Think "DNS = 53" - remember the phrase "DNS translates names, and it takes the 53rd step to find them." Also remember that ping works at the IP level and bypasses DNS, which is your key clue that DNS - not connectivity - is the problem.

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