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glossary
Proxy Node (Relay): A lightweight UDP relay server (~500KB RAM) that forwards game traffic between your PC and game servers through a faster backbone path. The client uses the community relay network by default; you can also run your own proxy on any Linux VPS.
Interceptor: The OS-level component that captures outbound game UDP packets before they leave your network interface and redirects them through the proxy. Uses nftables/iptables (Linux), pfctl (macOS), or WinDivert (Windows).
Tunnel: The encapsulated UDP connection between your PC and the proxy node. Game packets are wrapped in a 20-byte LightSpeed header that preserves the original source/destination IPs.
Session Token: An 8-bit authentication token assigned by the proxy during registration. Included in every data-plane packet to prevent unauthorized relay usage.
FEC (Forward Error Correction): XOR-based packet loss recovery. For every K data packets, one parity packet is sent. If any single packet in the block is lost, it can be reconstructed from the remaining packets. Uses ~25% bandwidth at the default K=4.
K (Block Size): Number of data packets per FEC parity packet. Default is 4 (25% overhead). Higher K = less overhead but less protection against burst loss.
RTT (Round-Trip Time): The time in milliseconds for a packet to travel from your PC to the relay and back. Measured continuously during keepalive probing.
RTT Saved: The difference between the direct (ICMP) round trip to the game server and the tunnelled round trip of the game traffic through the relay. Because ICMP and game traffic are different instruments, the figure is an estimate rather than a like-for-like measurement of in-game latency. It is the core value metric LightSpeed reports, and the relay aggregates it (k>=3) for the "RTT saved by LightSpeed" figure on the website.
Keepalive: Periodic empty packets sent between client and proxy to measure RTT and maintain the session. Sent every 5 seconds.
Multipath: Sending data packets on one path and FEC parity packets on a secondary path. If the primary path drops a packet, it's recovered from the parity on the secondary path.
Interceptor Mode (--start-interceptor): Kernel-level MITM that transparently redirects game traffic through the proxy. No game configuration needed - the game connects normally.
Redirect Mode (--game-server): The game connects to localhost on a specific port, and LightSpeed forwards traffic to the real server through the proxy. No root required.
Capture Mode (--capture): Uses libpcap to read packets from a network interface. Requires the pcap-capture feature and elevated privileges.
Watch Mode (--watch): Monitors for a game process and automatically starts the interceptor when the game launches.
Tunnel Header: 20-byte binary header prepended to every game packet in the tunnel. Contains version, flags, session token, sequence number, timestamp, and original source/destination IP/port.
FEC Header: 4-byte extension appended after the tunnel header when FEC is active. Contains block ID, packet index, and block size.
Control Plane: QUIC-based channel for proxy registration, session token distribution, and health checks. Separate from the data plane (UDP tunnel).
Data Plane: The actual UDP tunnel carrying game packets. Unencrypted by design to remain compatible with anti-cheat systems.
Community Relay Network: The default set of eight sponsor-funded relays (Los Angeles, New Jersey, Singapore, Frankfurt, Tokyo, Mumbai, Madrid, Sydney) that the client discovers through a signed registry. Free to use, no setup required.
VPS (Virtual Private Server): A cloud-hosted virtual machine running Linux. LightSpeed proxies run on VPS instances with as little as 512MB RAM.
systemd: Linux service manager. The proxy runs as a systemd service for automatic startup and crash recovery.
GHCR (GitHub Container Registry): Where pre-built Docker images of the proxy are published: ghcr.io/shibbityshwab/lightspeed-proxy.
EAC (EasyAntiCheat): Used by Rust, Fortnite, Apex Legends. Compatible with LightSpeed.
VAC (Valve Anti-Cheat): Used by CS2, Dota 2. Compatible.
BattlEye: Used by Fortnite, PUBG. Compatible.
Riot Vanguard: Used by Valorant, League of Legends. Compatible.
Blizzard Warden: Used by Overwatch 2. Compatible.