N10-005 · Question #724
An administrator needs to open ports in the firewall for both DNS and eDNS. Which of the following default ports would need to be opened on the firewall? (Select TWO).
The correct answer is B. TCP 53 E. UDP 53. DNS uses both TCP port 53 for zone transfers and large responses, and UDP port 53 for standard queries, so both must be opened in a firewall for full DNS functionality.
Question
An administrator needs to open ports in the firewall for both DNS and eDNS. Which of the following default ports would need to be opened on the firewall? (Select TWO).
Options
- ATCP 23
- BTCP 53
- CTCP 123
- DUDP 23
- EUDP 53
- FUDP 123
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Why each option
DNS uses both TCP port 53 for zone transfers and large responses, and UDP port 53 for standard queries, so both must be opened in a firewall for full DNS functionality.
TCP 23 is the well-known port for Telnet, an unencrypted remote administration protocol, and has no relationship to DNS.
TCP 53 is required for DNS zone transfers between authoritative servers and for responses exceeding 512 bytes, such as DNSSEC-signed records, making it necessary for complete DNS operation.
TCP 123 is not a standard assigned port; NTP (Network Time Protocol) uses UDP 123, not TCP 123.
UDP 23 is not assigned to any standard well-known protocol and has no relationship to DNS.
UDP 53 is the primary transport for standard DNS queries and responses due to its low overhead; most day-to-day DNS lookups use this port.
UDP 123 is the port for NTP (Network Time Protocol) used for time synchronization, not for DNS.
Concept tested: DNS port numbers TCP 53 and UDP 53
Source: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
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