What is mDNS (Multicast DNS) and DNS-SD (DNS Service Discovery), and what common consumer application uses both to enable automatic device discovery?

• A.mDNS (RFC 6762) resolves hostnames to IP addresses on a local network without a central DNS server, using multicast address 224.0.0.251 (IPv4) / FF02::FB (IPv6) on UDP 5353; DNS-SD (RFC 6763) uses mDNS records (PTR, SRV, TXT) for service discovery. Apple Bonjour uses both: it auto-discovers printers (_ipp._tcp.local), AirPlay speakers, and Chromecast devices on the local network segment
• B.mDNS is a Microsoft-only technology; DNS-SD is the Linux equivalent. They are incompatible with each other
• C.mDNS replaces standard unicast DNS in enterprise networks; it scales to millions of devices without a DNS server
• D.mDNS uses TCP for reliable service discovery; DNS-SD uses UDP for faster but lossy device announcements