UDP

UDP (User Datagram Protocol) is a minimal transport that fires packets at a destination without establishing a connection or guaranteeing they arrive in order — or at all. That lack of ceremony makes it fast and lightweight, ideal for traffic where a little loss is better than delay: live voice and video, gaming, DNS lookups and, increasingly, QUIC. Any reliability an application needs it must add itself. This is the direct trade-off against TCP, which guarantees delivery but adds the latency of handshakes and retransmissions.

UDP is where proxy support gets uneven. Classic HTTP proxies and the CONNECT method are built around TCP and do not relay UDP, whereas SOCKS5 can — and the s4m SOCKS5 proxy on port 1080 relays both TCP and UDP. Because HTTP/3 and QUIC ride on UDP, this determines whether they can pass through a given proxy at all. The device-wide s4m VPN tunnels UDP along with everything else, so if a UDP-based protocol will not traverse a TCP-only proxy, the VPN is the straightforward alternative.

SOCKS5 defines UDP ASSOCIATE, but UDP works only when the client, proxy configuration and network path all support it. A SOCKS5 label or an open TCP port 1080 does not prove that datagrams can pass. Classic HTTP CONNECT carries TCP, not UDP. QUIC and HTTP/3 therefore need a working UDP path; test the actual application and endpoint. A VPN can carry routed UDP traffic, subject to its routes and filtering; split tunneling or an application bypass can still send traffic outside the tunnel.