CompTIA Network+ (N10-009)Networking ConceptsEasy
A technician cannot resolve hostnames to IP addresses from a client workstation, though the workstation can ping IP addresses directly. Which port should the technician verify is open on the firewall between the client and the DNS server?
- AUDP 67
- BUDP/TCP 53
- CTCP 443
- DTCP 3389
Show answer & explanationAnswer & explanation
Correct answer: B. UDP/TCP 53
DNS uses port 53 for both queries (typically UDP) and zone transfers (TCP). If this port is blocked, name resolution fails even though IP-based connectivity works fine.
Why the other options are wrong
- A. Port 67 is used by DHCP servers, not DNS.
- C. Port 443 is used for HTTPS traffic.
- D. Port 3389 is used for RDP remote desktop sessions.
DNS Port 53
DNS translates hostnames to IP addresses and operates over port 53, using UDP for standard queries and TCP for larger responses or zone transfers.
- UDP 53 for typical queries
- TCP 53 for zone transfers and large responses
- Blocking port 53 breaks name resolution but not raw IP connectivity
Memory trick: Dial 53 to find the name behind the number.