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~/ports / 853

Port 853: DNS over TLS (DoT)

Port 853 carries encrypted DNS: TCP for DNS over TLS, UDP for DNS over QUIC.

Port
853
Protocol
TCP/UDP
Service
DNS over TLS / DNS over QUIC
Exposure
Public: only for your own DoT resolver
daniele@mikweb: ~/ports — less 853.md

Port 853/TCP is registered for DNS over TLS (DoT, RFC 7858), 853/UDP for DNS over QUIC (RFC 9250). Android uses DoT for its "Private DNS" feature, and resolvers like Unbound can forward queries to upstreams via DoT.

Open it only if you deliberately run a DoT resolver for your own clients – and restrict access, otherwise it is an open resolver. Outbound 853 from servers is usually fine.

Typical: restrictive networks block 853 and Android reports "Private DNS server cannot be accessed". DNS over HTTPS (DoH) on 443 is harder to block, but also harder to control.

Check

kdig @dns.example.com +tls example.com A
daniele@mikweb: ~/ports — ls

Ports

53/TCP/UDPDNS443/TCP/UDPHTTPS / HTTP/3

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