A port is a number from 0 to 65535 that tells a device which service a network connection is for, such as 443 for HTTPS or 53 for DNS.
Explanation
An IP address gets data to the right machine; the port gets it to the right program on that machine. Well-known services have registered numbers: web traffic uses 80 (HTTP) and 443 (HTTPS), DNS uses 53, DNS over TLS 853, SSH 22. VPNs have their own defaults: OpenVPN 1194, WireGuard 51820, IKEv2 500 and 4500. Each port can be TCP, UDP or both. HTTP/3 uses UDP port 443, while classic HTTPS uses TCP 443. Port numbers are the cheapest thing a firewall can filter on. Blocking UDP 51820 stops default WireGuard, and blocking 853 stops DNS over TLS, all without inspecting any content. That is why office and school networks often allow only 80 and 443. It is also why circumvention tools try to look like ordinary HTTPS on 443, since blocking that port breaks the whole web. A web proxy needs nothing else. On 15 October 2026 AnyProxy's regional hosts answered HTTPS on TCP 443 and advertised HTTP/3 on UDP 443 (alt-svc: h3=":443"). A network that blocks UDP only pushes the browser back to TCP 443 and HTTP/2. Port filtering cannot single the proxy out; name or address filtering still can.
In practice
AnyProxy's sessions use exactly the ports every website uses. sg., fr. and us.anyproxy.site accepted TLS 1.3 on TCP 443 and each advertised alt-svc: h3=":443", which means HTTP/3 on UDP 443, in checks on 15 Oct 2026. Compare a default WireGuard VPN on UDP 51820 or OpenVPN on 1194: one firewall rule removes them, while removing 443 would break every site on the network.
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