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Arjen
93ab8e4f62
A send on the active path that fails because the path is gone marks it
Suspect, and the next fast tick moves traffic to a live standby. Only
the kernel's unreachable errors (ENETUNREACH, EHOSTUNREACH) counted as
that. A connection-oriented transport has no route errors: when its
link drops it reports NotConnected (TCP, Tor, Nym) or, on BLE, an
untyped SendFailed("not connected"). Neither moved the path, so a dead
BLE or TCP path kept carrying a peer's traffic until the discretionary
switch. Seen on a phone moved from one USB cable to another while also
linked over BLE: every send failed "not connected" for 66 s, with a live
2 ms path beside it, before a discretionary switch took it.
`TransportError::is_unreachable` now also matches NotConnected, and BLE
returns the typed NotConnected for a send with no connection behind it.
Only a Live path is marked, so a path still connecting is untouched; the
background redial `send_nowait` already starts on NotConnected still
runs, and the path's own probes bring it back once it answers. With no
standby, Suspect changes nothing and the peer is not removed. BLE's
typed error also lets a msg1 reply take the same arrival-address
fallback TCP already takes in `handshake.rs`.
`a_send_that_finds_the_active_link_gone_moves_traffic_to_the_live_standby`
fails a dual-homed pair's cable sends with NotConnected (a test-only
switch on the loopback transport) and checks the cable goes Suspect and
traffic moves to the wifi on the next tick; it fails without the change.
FIPS Design
Architectural and protocol-level explanations for FIPS — the why and the how behind the wire and the system. For wire formats and configuration keys, see reference/. For task recipes, see how-to/. For end-to-end lessons, see tutorials/.
Reading Order
Start with fips-concepts.md for the novice-friendly framing of what FIPS is and why, then move to fips-architecture.md for the protocol stack, identity model, and two-layer encryption walkthrough. From there, follow the protocol stack from bottom to top. After the stack, fips-mesh-operation.md explains how the pieces work together at runtime. Cross-cutting and supporting documents cover specific subsystems in detail.
Foundations
| Document | Description |
|---|---|
| fips-concepts.md | What FIPS is, why it exists, mental model |
| fips-architecture.md | Protocol stack, identity, two-layer encryption |
| fips-prior-work.md | Designs and protocols FIPS builds on |
Protocol Stack
| Document | Description |
|---|---|
| fips-transport-layer.md | Transport layer: datagram delivery over arbitrary media |
| fips-mesh-layer.md | FIPS Mesh Protocol (FMP): peer authentication, link encryption, forwarding |
| fips-session-layer.md | FIPS Session Protocol (FSP): end-to-end encryption, sessions |
| fips-ipv6-adapter.md | IPv6 adaptation: TUN interface, DNS, MTU enforcement |
| fips-native-api.md | Native datagram API: pubkey-addressed flows over FSP, and what it is instead of the TUN path |
Cross-Cutting
| Document | Description |
|---|---|
| fips-mmp.md | Metrics Measurement Protocol (link + session) |
| fips-mtu.md | Path MTU model, encapsulation overhead, PMTUD |
| fips-multi-path-switchover.md | One peer, several paths: probe/ack, per-path heartbeats, measured selection, switchover without a second handshake |
| fips-security.md | fips0 interface threat model and default-deny baseline |
Mesh Behavior
| Document | Description |
|---|---|
| fips-mesh-operation.md | How the mesh operates: routing, discovery, error recovery |
| fips-nostr-discovery.md | Optional Nostr-mediated peer discovery and UDP NAT hole-punch |
| port-advertisement-and-nat-traversal.md | Nostr-signaled port advertisement and UDP NAT-traversal protocol; generic, with FIPS as an example implementation |
Deeper Dives
| Document | Description |
|---|---|
| fips-spanning-tree.md | Spanning tree algorithms: root discovery, parent selection, coordinates |
| fips-bloom-filters.md | Bloom filter properties: FPR analysis, size classes, split-horizon |
| spanning-tree-dynamics.md | Spanning tree walkthroughs: convergence scenarios, worked examples |
Adjacent Components
| Document | Description |
|---|---|
| fips-gateway.md | fips-gateway service: outbound (LAN-to-mesh) DNS-proxy + virtual-IP NAT and inbound (mesh-to-LAN) port-forwarding, sharing one nftables table |