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300-365 · Question #76
300-365 Question #76: Real Exam Question with Answer & Explanation
The correct answer is C: UDP 5353. mDNS (Multicast DNS) uses UDP port 5353 to allow devices to advertise and discover services on a local network without a central DNS server.
Question
Which protocol/port number is used by mDNS for service advertisement?
Options
- ATCP 5353
- BUDP 53
- CUDP 5353
- DTCP 53
Explanation
mDNS (Multicast DNS) uses UDP port 5353 to allow devices to advertise and discover services on a local network without a central DNS server.
Common mistakes.
- A. mDNS does not use TCP; the protocol relies on multicast UDP datagrams, and TCP cannot address multicast groups.
- B. UDP 53 is the standard unicast DNS port used by traditional DNS resolvers, not by mDNS service advertisement.
- D. TCP 53 is reserved for standard DNS zone transfers and large DNS responses, and is unrelated to multicast service discovery.
Concept tested. mDNS protocol and port for service discovery
Reference. https://www.rfc-editor.org/rfc/rfc6762
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