Build a server browser with NAT traversal fallback (STUN, then TURN/relay) for a peer-hosted indie multiplayer game
domain: datatracker.ietf.org · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Have each host register its session with a lightweight lobby/list service including host metadata (name, map, player count, region) for the server browser UI to query and display.
Attempt direct peer-to-peer connection first using STUN (RFC 5389) to discover each peer's public IP:port via hole punching, which works for most home routers with standard NAT behavior.
Detect STUN failures (symmetric NAT, restrictive firewalls) by timing out the direct connection attempt, then fall back to a TURN relay server that forwards traffic between peers who can't punch through directly.
Budget dedicated bandwidth/hosting cost for the TURN relay path, since relayed traffic consumes your server's bandwidth for the full session duration rather than just the handshake, unlike STUN.
Expire and remove stale entries from the server browser list with a heartbeat/TTL so closed or crashed host sessions don't linger in the list players can attempt to join.
Known gotchas
Symmetric NAT (common on mobile carriers and some corporate/school networks) defeats simple STUN hole punching entirely, so any indie multiplayer game without a TURN fallback will have players who simply can't connect to each other.
Running your own TURN server means it's a bandwidth cost center that scales with concurrent relayed sessions, not just connection count — budget for worst-case simultaneous relay load, not average.
A server browser list without server-side heartbeat verification can be spoofed/griefed with fake listings; validate that a listed host is actually reachable before showing it, or players will report "ghost" servers.
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