DNS / DNS-SD
DNS resolves names and DNS-SD describes discoverable services using PTR, SRV and TXT records. DNS-SD can use unicast DNS or local mDNS; it is not itself a separate transport port.
Scope: DNS / DNS-SD — requirements depend on the selected profile.
protocol · Catalog reviewed 2026-09-27
RFC 1035 / RFC 6763
DiscoveryOpen Standard
Infrastructure Requirements
- Reachable configured resolvers and authoritative records
- correct service records for DNS-SD
- trust configuration for encrypted DNS where used.
Network & Physical Requirements
| Port / allocation | Transport | Connection / signal flow | Feature and requirement | Evidence |
|---|---|---|---|---|
| 53 | TCP/UDP | DNS client → Configured DNS resolver | Profile requirement · Core DNS queries and responses DNS over UDP/TCP | Source checked 2026-09-27 RFC 1035, Sections 4.2.1 and 4.2.2: UDP and TCP usage |
| 853 (default) | TCP | DNS client → DoT resolver | Optional · Encrypted DNS DNS over TLS DNS over TLS | Source checked 2026-09-27 RFC 7858, Section 3.1: Session Initiation |
| 443 (default) | TCP | DNS client → DoH resolver | Optional · DoH DNS over HTTPS Configured DoH URI | Source checked 2026-09-27 RFC 8484, Sections 4.1 and 8.1: HTTPS URI and default port |
Gotchas & IT Notes
- ⚠Allow TCP as well as UDP for conventional DNS. Restrict resolver destinations; a DNS-SD service record advertises the actual service port.