Both variants of SessionMessageType were never emitted anywhere
in src/, and the production from_byte dispatch sites lacked
Some-arms for them — any 0x00/0x01 byte that reached either
dispatcher would log "Unknown..." and drop. The matching rustdoc
tables described an Offset 0 msg_type byte that the encode() path
has never written; the actual wire format is the FSP common prefix
[ver_phase][flags][payload_len:2 LE] with body keyed by phase
nibble, as documented in docs/reference/wire-formats.md.
Drop the variants, drop their from_byte/to_byte/Display arms, fix
the two stale rustdoc tables to describe the real wire shape, and
trim the variant-iteration unit test that enumerated them.
Zero on-wire behaviour change.
The test used Identity::generate() for the signing node while pinning
the fixed root to node_addr byte[0]=0x01. About 2/256 random identities
have byte[0] <= 0x01, which made the generated node_addr the path
minimum and triggered AncestryRootNotMinimum. Regenerate the identity
until its node_addr is numerically larger than the fixed parent and
root, so the test matches the preconditions it asserts.
Adds TreeAnnounce::validate_semantics() called from handle_tree_announce
before any tree-state mutation. Enforces that the ancestry accompanying
a parent declaration conforms to the spanning tree rules:
- first ancestry entry matches the signed sender
- is_root declarations carry a single-entry ancestry
- non-root declarations include the signed parent as the second entry
- the advertised root is the minimum node_addr in the ancestry
Non-conforming announcements are rejected with a warn log and no state
change. Adds unit tests for each rejected shape plus an integration
test covering the full receive path in a two-node tree.
Co-authored-by: Johnathan Corgan <johnathan@corganlabs.com>
Replace discovery flooding with bloom-filter-guided tree routing:
lookups sent only to tree peers (parent + children) whose bloom
filter contains the target. If no tree peer matches, fall back to
non-tree peers with bloom matches before dropping the request. This
produces single-path forwarding through the spanning tree (90%
traffic reduction) while recovering from dead ends caused by stale
bloom filters, tree restructuring, or transit node failures.
Remove visited bloom filter from LookupRequest wire format (-257
bytes per request). Tree routing is inherently loop-free; request_id
dedup handles edge cases during tree restructuring. Add response-
forwarded flag to prevent response routing loops from convergent
request paths.
Add originator-side exponential backoff (30s base, 300s cap) after
lookup timeouts and bloom misses. Backoff resets on topology changes
(parent switch, new peer, first RTT, reconnection).
Add transit-side per-target rate limiting (2s minimum interval) for
forwarded lookups as defense-in-depth.
Add discovery retry within the timeout window (default: send at T=0,
retry at T=5s, fail at T=10s) to compensate for single-path fragility.
Lookups with zero eligible tree peers fail immediately.
Improve discovery logging: promote key events to info (initiation,
success, timeout with failure count). Add debug logging for dedup,
pending packet retry, backoff suppression, forward rate limiting,
and backoff reset.
New config: discovery.backoff_base_secs, backoff_max_secs,
forward_min_interval_secs, retry_interval_secs, max_attempts.
New stats: req_backoff_suppressed, req_forward_rate_limited,
req_bloom_miss, req_no_tree_peer, req_fallback_forwarded.
Removed: req_already_visited, visited bloom filter.
Breaking wire format change: DataPacket payloads inside the AEAD envelope
now carry a 4-byte port header [src_port:2 LE][dst_port:2 LE] before the
service payload. The receiver dispatches by destination port.
Port multiplexing:
- send_session_data() takes src_port/dst_port params, prepends port header
- New send_ipv6_packet() compresses IPv6 header and sends on port 256
- Receive path dispatches DataPackets by port: port 256 decompresses IPv6
header from session context and delivers to TUN, unknown ports dropped
- Port constants: FSP_PORT_HEADER_SIZE (4 bytes), FSP_PORT_IPV6_SHIM (256)
IPv6 header compression:
- New ipv6_shim module with compress_ipv6()/decompress_ipv6() pure functions
- Strips src/dst addresses (32 bytes) and payload length (2 bytes) from each
packet, preserving traffic class, flow label, next header, and hop limit
as 6-byte residual fields
- Addresses reconstructed from session context on receive side
- Net savings: 29 bytes per packet (overhead 106 → 77 bytes)
- FIPS_IPV6_OVERHEAD constant (77 bytes), effective_ipv6_mtu() updated
- 16 unit tests for round-trip fidelity, field preservation, error cases
Documentation:
- fips-wire-formats: DataPacket port header, port registry, IPv6 shim
format tables, updated encapsulation walkthrough and overhead budget
- fips-ipv6-adapter: FIPS_IPV6_OVERHEAD (77 bytes), updated MTU numbers,
TUN reader/writer flow with compression steps, impl status
- fips-session-layer: port-based service dispatch section, data transfer
description, impl status
- fips-intro: IPv6 adapter as port 256 service, node architecture updated
- fips-mesh-operation: packet size summary with compressed overhead
- DataPacket doc updated with port header and dispatch model
- session_wire.rs module doc: DataPacket Port Multiplexing section
Bump rand (0.8→0.10), rtnetlink (0.14→0.20), tun (0.7→0.8),
simple-dns (0.9→0.11), socket2 (0.5→0.6), and criterion (0.5→0.8).
Migrate all rand call sites: thread_rng()→rng(), gen()→random(),
gen_range()→random_range(), RngCore→Rng trait. Work around secp256k1
0.30 requiring rand 0.8 by generating random bytes directly and
constructing SecretKey from slice.
Migrate rtnetlink to builder-based API: LinkSetRequest replaced with
LinkUnspec builder + change(), RouteAddRequest replaced with
RouteMessageBuilder.
Remove bloom benchmark (criterion 0.8 incompatible with old harness
config).
The session-layer handshake now uses the 3-message XK pattern instead
of the 2-message IK pattern, providing stronger initiator identity
hiding. The initiator static key is deferred to msg3 and encrypted
under the es+ee DH chain, so eavesdroppers cannot identify the
initiator from the handshake.
XK pattern: -> e, es (msg1) / <- e, ee + epoch (msg2) / -> s, se + epoch (msg3)
Key changes:
- Add XK handshake methods alongside existing IK methods in noise module
- Add SessionMsg3 wire format and FSP_PHASE_MSG3 (0x03) prefix
- Replace Responding state with AwaitingMsg3 in session state machine
- Rewrite session handlers: handle_session_setup defers identity to msg3,
handle_session_ack processes msg2 and sends msg3, new handle_session_msg3
completes the responder handshake and registers identity
- Link-layer (FMP) continues to use Noise IK unchanged
- Add comprehensive XK unit tests and update all integration tests
Add min_mtu (u16) to LookupRequest and path_mtu (u16) to
LookupResponse, enabling the discovery system to report transport
MTU capability along the lookup path.
LookupRequest carries min_mtu (origin's minimum MTU requirement,
default 0 = no requirement). LookupResponse carries path_mtu
(initialized to u16::MAX by the target, reduced by transit nodes
via min(path_mtu, outgoing_link_mtu) on the reverse path).
path_mtu is a transit annotation like SessionDatagram.path_mtu and
is NOT included in the proof signature. The originator stores the
discovered path_mtu in CacheEntry alongside cached coordinates.
Wire format: +2 bytes each for LookupRequest and LookupResponse.
Add a new session-layer error signal that transit routers send back to
the source when a forwarded packet exceeds the next-hop transport MTU.
This complements the existing proactive path MTU discovery (min'd at
each hop) by providing immediate feedback when oversized packets are
dropped, closing the transient window before the proactive mechanism
converges.
Wire format: 36-byte payload (msg_type + flags + dest_addr + reporter +
mtu) with FSP phase=0x0 and U flag set, matching the existing
CoordsRequired/PathBroken pattern.
Changes:
- Add SessionMessageType::MtuExceeded (0x22) and MtuExceeded struct with
encode/decode methods to protocol/session.rs
- Add NodeError::MtuExceeded variant to propagate structured MTU info
from TransportError through send_encrypted_link_message()
- Catch MtuExceeded in the forwarding path and send error signal back to
the datagram source via send_mtu_exceeded_error(), rate-limited by the
existing routing_error_rate_limiter
- Handle incoming MtuExceeded at the source by calling
PathMtuState::apply_notification() for immediate MTU decrease
- Add unit tests for encode/decode roundtrip, boundary MTU values, and
too-short payload rejection
Include target_coords in proof_bytes() signed data to prevent transit
nodes from substituting fake coordinates. Add mandatory signature
verification at the originator using the target's public key from
identity_cache (guaranteed available since lookups are only initiated
from contexts where the key is already cached).
Verification failure discards the response. Identity cache miss (should
never happen) logs an error and discards. Add four new tests covering
verification success, failure, cache miss, and coordinate substitution
detection.
Rename FIPS Link Protocol (FLP) to FIPS Mesh Protocol (FMP)
The "Link Protocol" name understated the layer's scope — spanning tree
construction, bloom filter routing, greedy forwarding, and mesh-wide
coordination go well beyond link-level concerns. Rename fips-link-layer.md
to fips-mesh-layer.md, update FLP→FMP throughout docs and source code
(FLP_VERSION→FMP_VERSION, wire.rs, rx_loop.rs, spanning_tree.rs).
New SVG illustrations
- Protocol stack: color-coded layer diagram replacing ASCII art
- OSI mapping: side-by-side comparison with traditional networking layers
- Bloom filter propagation: 6-node tree with sender-colored filter boxes
showing split-horizon computation per link
- Routing decision flowchart: 5-step priority chain with candidate ranking
by tree distance and link performance
- Coordinate discovery: sequence diagram showing LookupRequest propagation,
response caching, and SessionSetup cache warming
Redesigned existing SVGs
- Architecture overview: uniform node layout, U-shaped encrypted link
connectors, separate end-to-end session line
- Node architecture: split Router Core into FSP and FMP layers, reorganize
transports into Overlay/Shared Medium/Point-to-Point categories
- Identity derivation: wider boxes, visible encode arrow, dashed npub line
fips-intro.md revisions
- Add inline references to prior work: Yggdrasil/Ironwood for coordinate
routing, Noise Protocol Framework for IK handshakes, WireGuard for
index-based session dispatch, Wikipedia for bloom filters, split-horizon,
and greedy embedding
- Add explanatory paragraphs after bloom filter diagram describing
split-horizon filter computation and candidate selection behavior
- Simplify transport abstraction language, remove I2P/LoRa references
- Fix LookupRequest wording ("propagates" not "floods"), note intermediate
node coordinate caching on lookup responses
- Rewrite architecture overview prose to match redesigned diagrams
SessionAck previously only carried the responder's coordinates
(src_coords). When the return path diverged from the forward path
(e.g., after tree reconvergence), transit nodes on the return path
lacked the initiator's coordinates and couldn't route the SessionAck
back, causing handshake timeouts.
Add dest_coords (initiator's coordinates) to the SessionAck wire
format, mirroring SessionSetup's design. Transit nodes now cache both
endpoints' coordinates when forwarding a SessionAck, making the return
path self-sufficient regardless of path asymmetry.
Root cause confirmed by churn-20 sim log analysis: the n04-n14
handshake failure was caused by n15 (return-path transit) lacking
n04's coordinates, not by stale tree routes through a downed node.
Sends a 1-byte encrypted heartbeat (0x51) to each peer every 10s.
If no frame is received from a peer within 30s, the peer is removed
via remove_active_peer(), triggering tree reconvergence, coord cache
flush, and bloom filter recomputation.
This fixes the critical bug where UDP peers that silently died
(e.g., container stopped) were never detected or removed, leaving
the spanning tree permanently stale.
Both intervals are configurable via node.heartbeat_interval_secs
and node.link_dead_timeout_secs.
Implement hybrid coordinate cache warming strategy: piggyback coords
via CP flag when they fit within transport MTU, send standalone
CoordsWarmup (0x14) message when they don't. On CoordsRequired or
PathBroken receipt, send CoordsWarmup immediately with source-side
rate limiting (default 2s per destination, configurable).
- Add CoordsWarmup = 0x14 session message type (empty body, CP flag)
- Add send_coords_warmup() following send_session_msg() pattern
- Restructure send_session_data() to send standalone warmup before
data packet when piggybacked coords exceed MTU
- Add immediate CoordsWarmup response in handle_coords_required()
and handle_path_broken() with per-destination rate limiting
- Add coords_response_interval_ms config (node.session)
- Add RoutingErrorRateLimiter::with_interval() constructor
- Zero transit-path changes: existing try_warm_coord_cache() handles
CoordsWarmup identically to CP-flagged data packets
- Update design docs (session layer, wire formats, mesh operation,
configuration)
FIPS_OVERHEAD was 150 but had two bugs: the session AEAD tag (16 bytes)
was listed in the comment but missing from the arithmetic, and the
coordinate budget (~60 bytes) was undersized and didn't belong in a
constant representing fixed data path overhead.
Corrected to 106 bytes (the actual fixed overhead without coordinates).
This increases effective_ipv6_mtu from 1322 to 1366 for standard
Ethernet, well above the IPv6 minimum of 1280.
Added a guard in send_session_data() that computes the total wire size
with coordinates before committing to include them. If adding coords
would exceed the transport MTU, the CP flag is skipped and the warmup
counter is not decremented. This prevents silently producing oversized
packets at tree depth 2+.
Updated design docs (ipv6-adapter, wire-formats, mesh-operation) with
corrected overhead values.
Session-layer encryption used an implicit nonce counter with no counter
on the wire, requiring packets to arrive in exact order. Under bulk
transfer load (e.g., SCP), UDP packet loss or reordering permanently
desynchronized sender/receiver counters, causing all subsequent
decryption to fail with no recovery.
Add an 8-byte counter field to the DataPacket wire format and switch
from implicit-counter decrypt() to decrypt_with_replay_check() which
uses the explicit wire counter plus a 2048-packet sliding replay
window — the same pattern already used at the link layer.
Wire format: msg_type(1) + flags(1) + counter(8) + payload_len(2) = 12
bytes (was 4). FIPS_OVERHEAD updated 127 → 135 bytes accordingly.
Add src_addr to SessionDatagram envelope (34-byte header: msg_type +
src_addr + dest_addr + hop_limit) so transit routers can route error
signals back to the packet's originator.
Reclassify CoordsRequired/PathBroken as link-layer error signals
(plaintext inside SessionDatagram) rather than e2e encrypted session
messages. Transit routers generate these when forwarding fails and
route them to src_addr; if source is also unreachable, drop silently.
Remove redundant src_addr/dest_addr/hop_limit from SessionSetup,
SessionAck, and DataPacket (now in envelope). DataPacket header
reduced from 36 to 4 bytes. Remove PathBroken.original_src.
Fix routing loop vulnerability: gate bloom filter path on having
cached dest_coords to prevent blind forwarding between peers.
Simplify select_best_candidate() to require coordinates.
Fix gossip protocol type codes (0x11->0x20, 0x12->0x30, 0x13->0x31)
for consistency across all design docs.
All 5 design docs updated and cross-checked for consistency.
335 tests pass, zero warnings.
Johnathan Corgan
Sats And SportsandJohnathan Corgan
Origami74andJohnathan Corgan