A malformed FilterAnnounce whose fill ratio produces an implausibly
high false-positive rate is mostly useless for routing and, once
merged into our outgoing filter via bitwise OR, propagates the
saturated state to tree peers one hop per announce tick. A saturated
filter also made estimated_count() return f64::INFINITY, which
compute_mesh_size summed into its cached estimate.
handle_filter_announce now rejects inbound FilterAnnounce whose
derived FPR exceeds `node.bloom.max_inbound_fpr` (new config field,
default 0.05 ≈ fill 0.549 at k=5). Rejection is silent on the wire,
logs at WARN, and increments a new `bloom.fill_exceeded` counter. The
peer's prior stored filter and filter_sequence are left unchanged so
a single rejected announce does not wipe the peer's existing
contribution to aggregation.
After a successful outgoing FilterAnnounce send, a rate-limited WARN
fires if our own filter's FPR exceeds the same cap, surfacing
aggregation drift. Limited to once per 60 seconds via a new
Node.last_self_warn field.
BloomFilter::estimated_count() now takes max_fpr and returns
Option<f64>. Returns None for saturated filters (regardless of cap)
or when the filter's FPR exceeds max_fpr. Callers updated: debug
logs render None as "—", the Debug impl uses f64::INFINITY as "no
cap" and prints "saturated" instead of inf, control-socket JSON
emits null, and compute_mesh_size propagates None into the already-
Option<u64> estimated_mesh_size field.
Replace fixed 1KB bloom filters with variable-size filters (512B-32KB)
that adapt to each node's position in the spanning tree.
Core changes:
- Internal storage: Vec<u8> → Vec<u64> for word-level operations
- Delta compression: XOR diff with word-level RLE, sequence-based
NACK protocol for full retransmit recovery
- Size conversion: fold (large→small) and duplicate (small→large)
with auto-converting merge for mixed-size filter combination
- Native-size storage: peer filters stored at advertised size for
full-resolution routing queries, converted only for outgoing filter
- Adaptive sizing: outgoing fill ratio drives step-up/step-down
between size classes with hysteresis (20%/5% thresholds)
- Filter size decoupled from FMP negotiation: announced dynamically
in filter updates, bit 7 and TLV field 1 removed from handshake
Wire format: FilterAnnounce gains flags byte (delta bit), base_seq
field, RLE-compressed payload. New FilterNack message (0x21) for
out-of-sequence delta recovery.
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.
Implement hop-by-hop ECN congestion signaling through the FMP layer,
transport-level congestion detection via kernel drop counters, and
chaos harness integration for end-to-end validation.
FMP/session ECN plumbing:
- Thread ce_flag parsed at link layer through dispatch_link_message,
handle_session_datagram, handle_session_payload, and
handle_encrypted_session_msg to session delivery
- Replace hardcoded false in session-layer record_recv() with actual
ce_flag, activating ecn_ce_count tracking in session MMP
ECN congestion detection and CE relay:
- Add EcnConfig (node.ecn.*) with configurable loss_threshold (5%)
and etx_threshold (3.0) for transit congestion detection
- Add send_encrypted_link_message_with_ce() that ORs FLAG_CE into FMP
header flags; original method delegates with ce_flag=false
- Compute outgoing_ce = incoming_ce || local congestion on next-hop
link, enabling hop-by-hop CE relay through transit nodes
IPv6 ECN-CE marking:
- Mark ECN-CE (0b11) in IPv6 Traffic Class on received DataPackets
before TUN delivery when FMP CE flag is set
- Only marks ECN-capable packets (ECT(0)/ECT(1)); Not-ECT packets
unchanged per RFC 3168
Transport congestion abstraction and UDP kernel drop detection:
- Add TransportCongestion struct to transport layer for transport-
agnostic local congestion indicators
- Replace tokio::UdpSocket with AsyncFd<socket2::Socket> using
libc::recvmsg() with ancillary data parsing
- Enable SO_RXQ_OVFL for kernel receive buffer drop counter on every
packet, wiring up previously-stubbed UdpStats.kernel_drops
- Add TransportDropState for per-transport delta tracking with 1s
tick sampling via sample_transport_congestion()
- Extend detect_congestion() with transport kernel drop check
alongside MMP loss metrics
Congestion monitoring and control:
- Add CongestionStats (ce_forwarded, ce_received, congestion_detected,
kernel_drop_events) to NodeStats with snapshot serialization
- Wire counters into forwarding path, session handler, and transport
drop sampling with rate-limited warn logging (5s interval)
- Expose congestion data in show_routing control query and
ecn_ce_count in show_mmp peer entries
- Add congestion counters to fipstop routing tab in two-column layout
Chaos harness integration:
- Add query_routing(), query_transports(), snapshot_all_congestion()
to chaos control module
- Add congestion/kernel-drop log analysis in logs module
- Add congestion-stress scenario: 10-node tree, 1 Mbps bandwidth,
5-10% netem loss, heavy iperf3 traffic
- Add IngressConfig for tc ingress policing with per-peer policer
filters simulating upstream bandwidth bottlenecks
- Add iperf3 JSON result capture to traffic manager for throughput
measurement across scenarios
- Add ECN A/B test scenarios (ecn-ab-on/off.yaml) with ingress
policing and comparison script
- Enable TCP ECN negotiation (tcp_ecn=1 sysctl) in container
entrypoint for end-to-end CE propagation
Tests:
- 10 ECN unit/integration tests: mark_ipv6_ecn_ce variants, CE relay
chain (3-node propagation), EcnConfig serde roundtrip
- 3 transport drop congestion detection unit tests
Documentation:
- Update fips-mesh-layer.md: replace outdated CE Echo stub with full
ECN Congestion Signaling section covering detection logic, CE relay,
IPv6 marking, session tracking, and monitoring counters
- Update fips-configuration.md: add node.ecn.* parameter table and
ecn block in complete reference YAML
- Update fips-transport-layer.md: add Congestion Reporting section
with TransportCongestion struct, congestion() trait method, and
per-transport status; document AsyncFd/recvmsg/SO_RXQ_OVFL in UDP
- Update chaos README: add congestion/ECN scenario docs, ingress
traffic control, and iperf3 JSON capture sections
- Update README.md: add ECN to features list and "What works today";
update transport and tooling entries
Johnathan Corgan