Skip to contentSOCKS5 vs SOCKS4: the technical differences
SOCKS4 and SOCKS5 look similar on the surface but differ in three ways that decide whether your traffic works at all: authentication, UDP support and remote DNS. Here is the precise, protocol-level comparison.
Two versions of the same idea
SOCKS is a low-level proxy protocol: instead of understanding HTTP, it simply relays a TCP (and, in v5, UDP) connection between your client and a destination. That protocol-agnostic design is why SOCKS works for anything — web, email, game traffic, SSH — not just browsers. SOCKS4 arrived first; SOCKS5, defined in RFC 1928, is the version nearly everything speaks today. The differences are few but decisive.
Both start with your client asking the proxy to connect to a target host and port. What changed between the versions is who can use the proxy, what kinds of traffic it carries, and where the target hostname gets resolved.
Three differences that actually matter
1. Authentication. SOCKS4 has no authentication method built in (SOCKS4a added only a userid field, easily forged). SOCKS5 defines proper authentication, most commonly username/password, so a proxy can gate access to paying or authorised users. This alone is why commercial proxies use SOCKS5.
2. UDP and IPv6. SOCKS4 is TCP-only and IPv4-only. SOCKS5 adds UDP relaying (via the UDP ASSOCIATE command) and native IPv6 addressing, so it can carry DNS, VoIP, QUIC and game traffic that SOCKS4 simply cannot. See UDP over SOCKS5 for that mechanism.
3. Remote DNS. With SOCKS5 you can ask the proxy to resolve the hostname (the socks5h mode in tools like cURL), so the lookup never leaves your machine and cannot cause a DNS leak. SOCKS4 resolves locally and sends only an IP.
Which to use, and what s4m speaks
For anything written after roughly the mid-1990s, use SOCKS5 — and specifically the socks5h variant so DNS is resolved remotely and hostnames stay private. SOCKS4 survives only in legacy tooling and on some public proxy lists, where its lack of authentication is exactly why those proxies are open (and risky). The practical rule: prefer SOCKS5 with credentials for privacy and reach; treat bare SOCKS4 as a testing-only curiosity.
s4m provides authenticated SOCKS5 on proxy.s4m.online:1080 and an HTTP proxy on port 3128 — see the proxy page and what is SOCKS5. Use socks5h://USER:[email protected]:1080 to get authentication, UDP capability and leak-free remote DNS in one endpoint. The free list includes SOCKS4 entries if you specifically need to test legacy behaviour, but SOCKS5 is the default you want.
Questions, answered
What is the main difference between SOCKS4 and SOCKS5?
SOCKS5 adds real authentication, UDP relaying, IPv6 support and remote DNS resolution — none of which SOCKS4 has. SOCKS4 is TCP-only, IPv4-only and effectively unauthenticated, so SOCKS5 is the modern default for anything that needs security or non-TCP traffic.
What does the "h" in socks5h mean?
It means the proxy resolves the hostname remotely instead of your local machine. Using socks5h:// keeps your DNS lookups off your own network, preventing a DNS leak that could reveal which domains you are visiting. Plain socks5:// resolves locally first.
Authenticated SOCKS5, done right
Connect to proxy.s4m.online:1080 with socks5h for authentication, UDP support and leak-free remote DNS in a single endpoint. Metered pay-as-you-go, with an HTTP proxy on 3128 too.
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