SOCKS5
Proxy protocol. RFC 1928 (1996). Application-agnostic — proxies TCP (and v5 also UDP). Distinct from HTTP proxy (HTTP only). Basis for Tor + many VPN implementations.
Authentication: none, username/password, or GSSAPI. ssh -D 1080 user@host creates a SOCKS5 proxy via SSH tunnel — classic trick for secure browsing from café wifi. Browsers + curl + git support SOCKS5 directly. Modern alternatives: WireGuard (full VPN), Tailscale (zero-config WireGuard), Cloudflare WARP. SOCKS lives on in: SSH dynamic forwarding, Tor (entry point), enterprise proxy stacks as DLP security tools.