220-801 · Question #322
By default, which of the following ports is used for DNS?
The correct answer is D. 53. DNS (Domain Name System) uses port 53 by default for both UDP (standard queries) and TCP (zone transfers and large responses).
Question
Options
- A21
- B25
- C50
- D53
How the community answered
(31 responses)- B3% (1)
- C3% (1)
- D94% (29)
Why each option
DNS (Domain Name System) uses port 53 by default for both UDP (standard queries) and TCP (zone transfers and large responses).
Port 21 is assigned to FTP (File Transfer Protocol) for the control connection, not DNS.
Port 25 is assigned to SMTP (Simple Mail Transfer Protocol) for email transmission between mail servers, not DNS.
Port 50 is assigned to the ESP (Encapsulating Security Payload) protocol used in IPSec VPNs, not DNS.
Port 53 is the IANA-assigned well-known port for DNS; UDP port 53 handles most standard name resolution queries due to low overhead, while TCP port 53 is used for zone transfers between DNS servers and for responses exceeding 512 bytes, as defined in RFC 1035.
Concept tested: DNS default port 53 - TCP and UDP
Source: https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/dns-over-tcp-udp-port-53
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