Files
fips/docs/design
Johnathan Corgan 40c67abbe6 Merge master into next, forward-porting each side onto the other
Five files conflicted and each needed a different call, because the two
lines had rewritten different halves of the same code.

The handshake handler takes next's version whole. master's entire change
there was three comment blocks and one widened debug_assert, and the
assert names HandshakePhase::ReceivedMsg1, a variant next's XX rewrite does
not have. Nothing semantic was dropped.

The peer reaper takes master's: reap_peers_on_transport is new and its
route_link_dead doc now describes both callers, which is true on this line
too.

The ethernet transport takes master's binder rewrite with next's wire
format re-applied on top. The send path, the receive path and the frame
tests merged to the 4-byte header on their own, but three sites are new in
master's rewrite and had never seen it: the Binding default and both arms
of the binder's MTU calculation still subtracted 3. The transports snapshot
fixture moved with them, 1499 to 1496, and that single field was the whole
diff. Beacons carry no pubkey here, so local_pubkey leaves the transport,
its binder context and the node's transport construction with it.

The changelog keeps both sides' entries, with master's Added subsection
lifted back out of Changed where the merge had left it.

Two tests do not come across. a_transient_msg2_failure_keeps_the_link_for_
the_retry and its restart-path sibling assert that the machine rests at
ReceivedMsg1. This line's nearest state is SentMsg2, and it means something
else: the inbound leg parks there awaiting msg3, where on the other line
that phase was the last stop before promotion. Renaming it would produce a
test that passes without exercising the deferral. The behaviour they guard
did merge and sits in the transient arm of the msg2 send failure; what is
missing is coverage shaped for this handshake, which is tracked separately.

The two connected-socket tests did come across. Their helper took the
responder's session straight after msg2, which is an IK assumption; it now
runs msg3 as well. Both pass here and both go red when the clear is removed
or made unconditional.

The test-harness fixes arrive through master rather than as follow-ups
here, so this line never carries the versions that failed: the
interface-binding suite's veth naming, and the chaos veth restore, random
streams, settle wait, netem restore and shared down-node set.
2026-09-10 19:19:27 +00:00
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2026-08-30 10:42:59 +00:00
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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-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