softlan-vpn/README.md

softlan-vpn

Monorepo for a Layer 2 over QUIC LAN party bridge.

Workspace crates

• lanparty-proto: shared frame format, MAC validation, MTU helpers.
• lanparty-ctrl: control-plane messages (join/hello/role/version).
• lanparty-net: shared relay endpoint parsing and resolution.
• lanparty-obs: shared diagnostics/logging event models.
• lanparty-client-core: platform-agnostic client session state.
• lanparty-client-route: Windows relay-route inspection.
• lanparty-client-tap: TAP-Windows6 adapter discovery and frame I/O.
• lanparty-client-win: Windows TAP + route/metric handling binary.
• lanparty-gateway: Linux AF_PACKET gateway binary.
• lanparty-relay: public QUIC relay binary.

lanparty-proto

Transport-agnostic tunnel contract shared by all binaries:

• overlay datagram header encoding and decoding
• negotiated QUIC datagram budget validation before send
• Ethernet frame header parsing
• MAC address parsing and identity validation
• QUIC datagram to TAP MTU budget helpers

lanparty-ctrl

Reliable control-plane schema shared by the QUIC stream handlers:

• endpoint hello messages with role, room, MAC, and datagram budget
• server welcome mode, reject, peer lifecycle, stats, and disconnect messages
• initial room gateway-presence status in server welcomes
• room-code, role/MAC, peer-id, and effective-MTU validation
• length-prefixed JSON control frames for reliable QUIC streams

lanparty-obs

Shared diagnostics and structured logging vocabulary:

• gateway/relay frame logs with MACs, ethertype, length, peer, and action
• tunnel counters shared by control messages and runtime diagnostics
• client connectivity/TAP diagnostics and user-facing status messages

lanparty-net

Shared network address handling for tunnel binaries:

• relay DNS name, IP literal, and socket-address parsing
• UDP/443 default for bare relay hosts
• relay address resolution before tunnel interface activation

lanparty-client-core

Platform-neutral remote client relay session:

• relay QUIC connection with pinned relay certificate trust
• client hello with room, virtual MAC, and datagram budget
• welcome/reject handling with assigned peer id and effective TAP MTU
• QUIC DATAGRAM support and negotiated datagram budget diagnostics
• relay RTT diagnostics from the active QUIC connection
• reliable relay control-event reads for peer lifecycle messages
• Ethernet frame send/receive helpers over QUIC DATAGRAM with budget and source MAC checks plus local drop outcomes for malformed or oversized sends
• client tunnel statistics for frame/datagram rx/tx and drops
• reliable client stats snapshot sends for relay diagnostics
• best-effort graceful disconnect messages before QUIC close

lanparty-client-route

Windows route-table boundary:

• read-only best-route lookup for a relay destination IP
• selected source address, next hop, interface index/LUID, prefix, and metric
• interface index/LUID lookup from Windows network adapter GUIDs
• scoped IP interface MTU overrides with restore-on-drop behavior
• scoped IP interface metric overrides with restore-on-drop behavior
• scoped default-route suppression with restore-on-drop behavior
• unicast IP address snapshots for TAP diagnostics
• scoped host-route pinning for the relay IP on the pre-TAP interface
• reuse of an already-existing matching relay host route without deleting it on exit
• non-Windows builds return a clear unsupported-platform error

lanparty-client-tap

Windows TAP adapter boundary:

• TAP-Windows6 adapter discovery from the Windows network adapter registry
• TAP NetworkAddress registry configuration for the tunnel MAC identity
• \\.\Global\{NetCfgInstanceId}.tap device path construction
• blocking Ethernet frame reads/writes through the TAP device handle
• TAP driver IOCTL helpers for media status, adapter MAC, and MTU

lanparty-relay

Public relay binary and relay-owned room state:

• QUIC endpoint binding and first-stream hello/welcome admission
• room admission for clients and gateways
• one gateway per room, duplicate client MAC rejection, and room limits
• stable effective room MTU chosen before Ethernet datagrams flow
• live Ethernet datagram forwarding with no ingress reflection
• per-peer egress budget checks against the negotiated datagram size
• reliable PeerJoined/PeerLeft notifications to existing room peers
• L2 safety filters for invalid-source, jumbo, switch-control, remote VLAN tags, remote IPv6 fragments, IPv4/IPv6 DHCP-server, and IPv6-RA frames, including frames behind ordinary IPv6 extension headers
• client broadcast/multicast, unknown-unicast, and total bandwidth limiting
• malformed peer datagram disconnect threshold
• peer stats control events retained for relay diagnostics
• graceful disconnect control events propagated as peer-leave reasons
• per-peer last-seen timestamps in relay room snapshots
• peer leave cleanup for room membership and MAC indexes

Build

cargo check --workspace

For the manual MVP end-to-end proof, see TESTING.md.

Relay

cargo run -p lanparty-relay -- --listen 443/udp --dev-cert-der-out relay-cert.der

--listen accepts either a socket address or a UDP port shorthand such as 443/udp. The relay binds a QUIC endpoint, accepts a control-stream hello, replies with welcome or reject, and forwards live Ethernet QUIC datagrams between accepted peers in the same room. It currently uses a generated self-signed development certificate; --dev-cert-der-out writes that certificate so the gateway and client can pin it in development. Production certificate handling remains future work. Ethernet forwarding decisions are logged with room, peer, MAC, ethertype, action, drop reason, and target count. Safety-policy rejects use the filtered action so they are distinguishable from malformed/unknown-destination drops and rate limits. Malformed peer datagrams log their per-peer count before the relay disconnects peers that cross the malformed-datagram threshold. Relay egress skips caused by a target peer's smaller datagram budget are logged with the ingress peer, target peer, encoded length, and target budget. Unknown unicast from a client is forwarded only to the gateway port; unknown unicast from the gateway is dropped instead of flooded to every remote client. When a peer joins or leaves, the relay sends a reliable lifecycle control event to peers that are still present in the room. Newly joined peers also receive PeerJoined events for peers that were already present.

MVP Trust Model

The MVP relay terminates QUIC for every client and gateway connection. QUIC protects traffic on the public network path, but the relay process sees plaintext Ethernet frames while forwarding them between peers in a room. That is acceptable for the first LAN-party proof, where the relay is an operator-trusted component, but it is not end-to-end encrypted.

Future room-key payload encryption should keep the relay-visible routing header small and leave only Ethernet payload bytes encrypted end-to-end between clients and the LAN gateway.

Gateway

cargo run -p lanparty-gateway -- \
  --relay lanparty-relay.local \
  --server-name lanparty-relay.local \
  --relay-ca-cert relay-cert.der \
  --room ROOM1 \
  --iface eth0

The gateway first opens the wired LAN interface as an AF_PACKET socket with promiscuous packet membership, then connects to the relay as role = gateway and completes the control-stream hello/welcome handshake. That startup order keeps an invalid, wireless, or unplugged interface from briefly advertising a gateway that cannot bridge. Once both sides are ready, it bridges Ethernet frames between the relay and wired LAN until shutdown. It captures whole LAN frames up to the overlay payload-length ceiling before deciding whether they fit the tunnel. It never fragments Ethernet frames; LAN frames with invalid source MACs, L2 control-plane traffic, jumbo frames, or encoded datagrams exceeding the negotiated QUIC budget are counted, dropped, and logged locally instead of stopping the bridge or consuming relay bandwidth. --relay accepts a DNS name or socket address; bare hosts default to UDP/443. The gateway rejects Linux interfaces that sysfs identifies as Wi-Fi, and rejects wired interfaces whose sysfs carrier state reports no link; managed wireless NICs are not supported for the physical LAN bridge. It tracks remote-client source MACs seen from relay traffic and periodically emits small CAM refresh frames so the physical switch keeps those MACs associated with the gateway port. Gateway frame logs include direction, peer id when present, MACs, ethertype/length, frame length, action, and drop reason. The gateway also tracks frame/datagram counters and periodically sends stats snapshots to the relay. Malformed or runt LAN frames are counted and logged as dropped instead of disappearing before accounting. Relay lifecycle events seed and retire remote-client MACs for CAM refresh even before that client sends traffic. On shutdown, the gateway sends a best-effort disconnect control message before closing QUIC so the relay can report the intended reason.

Windows Client

cargo run -p lanparty-client-win -- \
  --relay lanparty-relay.local \
  --server-name lanparty-relay.local \
  --relay-ca-cert relay-cert.der \
  --room ROOM1

The Windows client binary currently connects to the relay as role = client with a generated locally administered virtual MAC persisted in lanparty-client-identity.json. Before resolving or connecting to the relay, it selects the TAP-Windows6 adapter and marks TAP media disconnected to clear stale connected state from a previous crashed run. It then resolves the relay DNS name before TAP activation, completes the control-stream hello/welcome handshake, pins a host route for the resolved relay IP on the current pre-TAP interface, verifies that the relay route still uses that pinned host route after TAP activation, and then bridges Ethernet frames between the relay and the first TAP-Windows6 adapter until shutdown. --relay accepts a DNS name or socket address; bare hosts default to UDP/443. Before opening the adapter for bridging, it writes the generated tunnel MAC to the TAP driver's NetworkAddress registry setting. TAP frames whose source MAC does not match that generated tunnel MAC are dropped locally before they can consume relay bandwidth; the relay still enforces the same source-MAC rule. If the exact relay host route already exists, the client uses it and leaves it alone on exit. The startup status reports whether the relay already has a LAN gateway for the room. --virtual-mac can still override the stored identity for manual testing. On Windows it sets the TAP IP interface MTU to the relay-selected MTU, marks the TAP media connected for the scoped client run, and reports the driver MAC/MTU before forwarding frames, along with the TAP interface index/LUID. The client applies a scoped TAP interface metric and disables TAP default routes while it runs, periodically rechecks that the relay route remains pinned, then restores the previous route policy and TAP media status on exit. Startup prints a warning when TAP default routes were enabled before the scoped protection was applied. Startup still fails before bridging if the driver-reported MAC does not match the tunnel identity, because an already-initialized Windows TAP adapter may need to be disabled/enabled or reinstalled before it reloads the configured NetworkAddress. If exactly one TAP-Windows6 adapter is installed, the client opens it automatically. If multiple TAP-Windows6 adapters are installed, startup fails until --tap-instance-id selects the intended adapter by NetCfgInstanceId / InterfaceGuid. --list-tap-adapters prints the TAP adapter ids and exits without connecting. It prints and reports client diagnostics snapshots with relay reachability, LAN-gateway presence, route-pinning, QUIC datagram budget, relay RTT, TAP status/IP, broadcast frame flow, frame/datagram counters, and drops. The periodic diagnostics refresh the TAP unicast IP so DHCP results that arrive after bridging starts become visible in later status lines. Each snapshot also emits short user-facing lines such as relay/gateway connection status, relay-route and TAP readiness warnings, DHCP address presence, relay RTT, and broadcast-flow confirmation when those signals are observed. Malformed frames read from TAP, invalid or unauthorized source-MAC frames, jumbo frames, and TAP frames whose encoded datagrams exceed the negotiated QUIC budget are counted and dropped before relay send without stopping the bridge; TAP device read/write errors still stop the bridge. Relay lifecycle events are logged as they arrive, including gateway joins and peer leaves. The client remembers peer identities from join and catch-up events so later leave logs can identify a disconnected LAN gateway or client MAC when that peer was known.