Port 853 (TCP) — DNS over TLS (DoT)
DNS over TLS encrypts stub-to-resolver DNS queries inside dedicated TLS sessions on TCP/853, preventing local Wi-Fi eavesdropping and ISP DNS hijacking.
| Port Number | 853 |
|---|---|
| Transport Protocol | TCP |
| Primary Service | DNS over TLS (DoT) |
| Standard / Specification | RFC 7858 |
| IANA Port Range | Well-Known System Port (0–1023) |
| Internet Exposure Risk | Safe outbound privacy protocol; enterprise networks should steer endpoints to approved resolvers. |
Firewall Architecture & Hardening Best Practices
Android Private DNS, systemd-resolved, and Stubby use outbound TCP/853 to resolvers such as 1.1.1.1 or 9.9.9.9. Blocking TCP/853 causes clients in opportunistic mode to fall back to UDP/53.
Operational Troubleshooting Note
Verify a DoT resolver handshake and certificate using kdig -d @1.1.1.1 +tls-ca +tls-host=cloudflare-dns.com example.com.
Quick CLI Connectivity & Firewall Reference
# Test TCP/853 reachability (Linux / macOS / PowerShell) nc -zv target.example.com 853 Test-NetConnection -ComputerName target.example.com -Port 853 # Allow restricted CIDR on Linux UFW firewall ufw allow from 10.0.0.0/8 to any port 853 proto tcp
Planning firewall allowlists or VPN overlays? Use our IPv4 CIDR Calculator, MTU & TCP MSS Calculator, or WireGuard AllowedIPs Generator.
Browse Common Network & Cloud Ports
Port 22 (SSH) Port 25 (SMTP Mail Relay) Port 53 (Domain Name System) Port 67 (DHCPv4 Server) Port 80 (HTTP Web Traffic) Port 123 (Network Time Protocol) Port 161 (SNMP Polling) Port 179 (Border Gateway Protocol) Port 389 (LDAP Directory) Port 443 (HTTPS & HTTP) Port 445 (SMB Direct File Sharing) Port 465 (SMTPS Implicit TLS Submission) Port 500 (IPsec IKEv2 Key Exchange) Port 514 (Syslog Telemetry) Port 587 (SMTP Mail Submission) Port 636 (LDAPS) Port 853 (DNS over TLS) Port 993 (IMAPS Encrypted Mailbox) Port 1194 (OpenVPN Tunnel) Port 1433 (Microsoft SQL Server) Port 1812 (RADIUS Authentication) Port 2049 (Network File System) Port 2379 (etcd Client API) Port 3306 (MySQL & MariaDB) Port 3389 (Remote Desktop Protocol) Port 4500 (IPsec NAT Traversal) Port 5432 (PostgreSQL Database) Port 6379 (Redis) Port 6443 (Kubernetes API Server) Port 51820 (WireGuard VPN)