Which port does the DNS protocol use for its query and reply messages?

• A. Port 80
• B. Port 22
• C. Port 443
• D. Port 53

Answer: (D)

DNS uses the well-known port 53 for its communications. When you perform a lookup, the DNS client sends a query to the DNS server on port 53, and the server responds back as part of the same conversation, delivering the reply to the client’s originating port. UDP is the primary transport for these queries and responses, though larger messages or certain operations may fall back to TCP on port 53. The other ports listed correspond to different services (80 for web, 22 for SSH, 443 for HTTPS) and aren’t used for DNS.