# FIPS Configuration

FIPS uses YAML-based configuration with a cascading multi-file priority system.
All parameters have sensible defaults; a node can run with no configuration file
at all (it will generate an ephemeral identity and listen on default addresses).

## Configuration Loading

### Search Paths

When started without the `-c` flag, FIPS searches for `fips.yaml` in these
locations, lowest to highest priority:

| Priority | Path | Purpose |
|----------|------|---------|
| 1 (lowest) | `/etc/fips/fips.yaml` | System-wide defaults |
| 2 | `~/.config/fips/fips.yaml` | User preferences |
| 3 | `~/.fips.yaml` | Legacy user config |
| 4 (highest) | `./fips.yaml` | Deployment-specific overrides |

All found files are loaded and merged in priority order. Values from higher
priority files override those from lower priority files. This allows a system
administrator to set site-wide defaults in `/etc/fips/fips.yaml` while
individual deployments override specific values in `./fips.yaml`.

### CLI Option

```text
fips -c /path/to/config.yaml
```

When `-c` is specified, only that file is loaded (search paths are skipped).

### Partial Configuration

Every field has a built-in default. A configuration file only needs to specify
values that differ from defaults. For example, a minimal config might contain
only the identity and peer list, inheriting all other defaults.

## YAML Structure

The configuration is organized into five top-level sections:

```yaml
node:        # Node behavior, protocol parameters, and tuning
tun:         # TUN virtual interface
dns:         # DNS responder for .fips domain
transports:  # Network transports (UDP, Ethernet, Bluetooth, Tor, ...)
peers:       # Static peer list
```

### Control Socket (`node.control.*`)

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.control.enabled` | bool | `true` | Enable the control socket |
| `node.control.socket_path` | string | *(auto)* | **Linux:** Socket file path. Resolved at daemon startup: `$XDG_RUNTIME_DIR/fips/control.sock` if `XDG_RUNTIME_DIR` is set, else `/run/fips/control.sock` if `/run/fips` can be created (typical when running under the shipped systemd unit), else `/tmp/fips-control.sock`. (Note: the `fipsctl` / `fipstop` clients use a different fallback order — `/run/fips` first if it already exists, then `XDG_RUNTIME_DIR`, then `/tmp` — so when both schemes apply, set this field explicitly to avoid mismatch.) **Windows:** TCP port number (default: `21210`); the control socket listens on `127.0.0.1` at this port. |

The control socket provides access to node state and runtime management
via the `fipsctl` command-line tool. In addition to read-only status
queries, `fipsctl connect` and `fipsctl disconnect` enable runtime peer
management. See the [`fipsctl` reference](cli-fipsctl.md) for the
command list.

On Linux, the control socket is a Unix domain socket with filesystem
permissions (mode 0770, group `fips`). On Windows, it is a TCP listener
on localhost. TCP does not provide filesystem-level ACLs, so any local
user can connect to the control port.

> **Security note (Windows):** The TCP control socket on Windows is a
> known limitation. Any process running on the local machine can connect
> to the control port and issue commands, including `disconnect`,
> `connect`, and `inject-config`. This is acceptable for single-user
> workstations but may be inappropriate for shared machines. Future
> improvements may include named pipe support (with Windows ACLs) or an
> authentication token mechanism. On shared Windows systems, consider
> using firewall rules to restrict access to the control port.

All tunable protocol parameters live under `node.*`, organized as sysctl-style
dotted paths. The top-level sections (`tun`, `dns`, `transports`, `peers`)
handle infrastructure concerns only.

## Node Parameters (`node.*`)

### Identity (`node.identity.*`)

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.identity.nsec` | string | *(none)* | Secret key in nsec (bech32) or hex format. If omitted, behavior depends on `persistent`. |
| `node.identity.persistent` | bool | `false` | Persist identity across restarts via key file. |

Identity resolution follows a three-tier priority:

1. **Explicit `nsec`** in config — always used when present, regardless of `persistent`
2. **Persistent key file** — when `persistent: true` and no `nsec`, loads from `fips.key`
   adjacent to the config file; if no key file exists, generates a new keypair and saves it
3. **Ephemeral** — when `persistent: false` (default) and no `nsec`, generates a fresh
   keypair on each start

Key files (`fips.key` with mode 0600, `fips.pub` with mode 0644) are written adjacent
to the highest-priority config file for operator visibility, even in ephemeral mode.

### General

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.leaf_only` | bool | `false` | Leaf-only mode: node does not forward traffic or participate in routing |
| `node.tick_interval_secs` | u64 | `1` | Periodic maintenance tick interval (retry checks, timeout cleanup, tree refresh) |
| `node.base_rtt_ms` | u64 | `100` | Initial RTT estimate for new links before measurements converge |
| `node.heartbeat_interval_secs` | u64 | `10` | Heartbeat send interval per peer for liveness detection |
| `node.link_dead_timeout_secs` | u64 | `30` | No-traffic timeout before a peer is declared dead and removed |
| `node.log_level` | string | `"info"` | Tracing filter default. Case-insensitive; one of `trace`, `debug`, `info`, `warn`, `error`. Overridden by the `RUST_LOG` environment variable when set |

### Resource Limits (`node.limits.*`)

Controls capacity for connections, peers, and links.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.limits.max_connections` | usize | `256` | Max handshake-phase connections |
| `node.limits.max_peers` | usize | `128` | Max authenticated peers |
| `node.limits.max_links` | usize | `256` | Max active links |
| `node.limits.max_pending_inbound` | usize | `1000` | Max pending inbound handshakes |

### Rate Limiting (`node.rate_limit.*`)

Handshake rate limiting protects against DoS on the Noise IK handshake path.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.rate_limit.handshake_burst` | u32 | `100` | Token bucket burst capacity |
| `node.rate_limit.handshake_rate` | f64 | `10.0` | Tokens per second refill rate |
| `node.rate_limit.handshake_timeout_secs` | u64 | `30` | Stale handshake cleanup timeout |
| `node.rate_limit.handshake_resend_interval_ms` | u64 | `1000` | Initial handshake message resend interval |
| `node.rate_limit.handshake_resend_backoff` | f64 | `2.0` | Resend backoff multiplier (1s, 2s, 4s, 8s, 16s with defaults) |
| `node.rate_limit.handshake_max_resends` | u32 | `5` | Max resends per handshake attempt |

### Retry / Backoff (`node.retry.*`)

Connection retry with exponential backoff.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.retry.max_retries` | u32 | `5` | Max connection retry attempts |
| `node.retry.base_interval_secs` | u64 | `5` | Base backoff interval |
| `node.retry.max_backoff_secs` | u64 | `300` | Cap on exponential backoff (5 minutes) |

Auto-reconnect (triggered by MMP link-dead removal) uses the same backoff
parameters but bypasses `max_retries`, retrying indefinitely. See
`peers[].auto_reconnect` below.

### Cache Parameters (`node.cache.*`)

Controls caching of tree coordinates and identity mappings.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.cache.coord_size` | usize | `50000` | Max entries in coordinate cache |
| `node.cache.coord_ttl_secs` | u64 | `300` | Coordinate cache entry TTL (5 minutes) |
| `node.cache.identity_size` | usize | `10000` | Max entries in identity cache (LRU, no TTL) |

### Discovery Protocol (`node.discovery.*`)

Controls bloom-guided node discovery (LookupRequest/LookupResponse).

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.discovery.ttl` | u8 | `64` | Hop limit for LookupRequest forwarding |
| `node.discovery.attempt_timeouts_secs` | array&lt;u64&gt; | `[1, 2, 4, 8]` | Per-attempt timeouts. Each entry is the deadline for one `LookupRequest` before sending the next attempt with a fresh `request_id`. Length determines total attempt count; default gives 4 attempts and a 15s total budget |
| `node.discovery.recent_expiry_secs` | u64 | `10` | Dedup cache expiry for recent request IDs |
| `node.discovery.backoff_base_secs` | u64 | `0` | Optional post-failure suppression base in seconds; doubles per consecutive failure. `0` disables (default) — the per-attempt sequence is the only retry pacing |
| `node.discovery.backoff_max_secs` | u64 | `0` | Cap on optional post-failure backoff |
| `node.discovery.forward_min_interval_secs` | u64 | `2` | Transit-side rate limiting: minimum interval between forwarded lookups for the same target |

#### Nostr Overlay Discovery (`node.discovery.nostr.*`)

Optional Nostr-mediated overlay discovery. This layer publishes replaceable
endpoint adverts (`fips-overlay-v1`), consumes advert-derived endpoint
fallbacks for configured peers, and can optionally discover non-configured
peers (`policy: open`). `udp:nat` remains the trigger for NAT traversal
offer/answer + punch-through, after which the established UDP socket is handed
into the normal FIPS transport/session stack.
Inbox-relay discovery falls back to the local DM relay list if remote relay
metadata cannot be fetched.
The Nostr discovery runtime is compiled into every build of the crate; it
is enabled at runtime via `node.discovery.nostr.enabled: true` and stays
inert otherwise.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.discovery.nostr.enabled` | bool | `false` | Enable Nostr-mediated overlay discovery |
| `node.discovery.nostr.policy` | string | `"configured_only"` | Advert discovery policy: `disabled`, `configured_only`, `open` |
| `node.discovery.nostr.open_discovery_max_pending` | usize | `64` | Max open-discovery peers queued in outbound retry/connection state at once |
| `node.discovery.nostr.max_concurrent_incoming_offers` | usize | `16` | Max concurrent inbound traversal offers processed at once (rate limit against offer spam) |
| `node.discovery.nostr.advert_cache_max_entries` | usize | `2048` | Max cached overlay adverts retained from relay traffic |
| `node.discovery.nostr.seen_sessions_max_entries` | usize | `2048` | Max seen-session IDs retained for replay detection |
| `node.discovery.nostr.advertise` | bool | `true` | Publish local endpoint adverts |
| `node.discovery.nostr.advert_relays` | list[string] | `["wss://relay.damus.io", "wss://nos.lol", "wss://offchain.pub"]` | Relays used for service adverts |
| `node.discovery.nostr.dm_relays` | list[string] | `["wss://relay.damus.io", "wss://nos.lol", "wss://offchain.pub"]` | Relays used for encrypted signaling events |
| `node.discovery.nostr.stun_servers` | list[string] | `["stun:stun.l.google.com:19302", "stun:stun.cloudflare.com:3478", "stun:global.stun.twilio.com:3478"]` | STUN servers used for local reflexive address discovery |
| `node.discovery.nostr.share_local_candidates` | bool | `false` | Whether to advertise local (RFC 1918 / ULA) interface addresses as host candidates in the traversal offer. Off by default: in most deployments peers aren't on the same broadcast domain, and sharing private host candidates causes misleading punch successes when an asymmetric L3 path (VPN, Tailscale subnet route, overlapping address space) makes a peer's private IP one-way reachable. Enable only when peers are on the same physical LAN |
| `node.discovery.nostr.app` | string | `"fips-overlay-v1"` | Traversal application namespace, published in the advert's `protocol` tag (the `d` tag itself is hardcoded to `fips-overlay-v1`) |
| `node.discovery.nostr.signal_ttl_secs` | u64 | `120` | Signaling TTL in seconds |
| `node.discovery.nostr.attempt_timeout_secs` | u64 | `10` | Overall traversal attempt timeout in seconds |
| `node.discovery.nostr.replay_window_secs` | u64 | `300` | Replay tracking retention window in seconds |
| `node.discovery.nostr.punch_start_delay_ms` | u64 | `2000` | Delay before punch traffic starts |
| `node.discovery.nostr.punch_interval_ms` | u64 | `200` | Interval between punch packets |
| `node.discovery.nostr.punch_duration_ms` | u64 | `10000` | How long to keep punching before failure |
| `node.discovery.nostr.advert_ttl_secs` | u64 | `3600` | Advert TTL in seconds |
| `node.discovery.nostr.advert_refresh_secs` | u64 | `1800` | How often adverts are refreshed in seconds |
| `node.discovery.nostr.startup_sweep_delay_secs` | u64 | `5` | Settle delay after Nostr discovery starts before the one-shot startup advert sweep runs (only used under `policy: open`). Allows the relay subscription backlog to populate the in-memory advert cache before the sweep fires |
| `node.discovery.nostr.startup_sweep_max_age_secs` | u64 | `3600` | Maximum advert age (`now - created_at`) considered by the one-shot startup sweep (only used under `policy: open`). Adverts older than this are skipped on startup; the per-tick sweep still considers them up to `valid_until_ms` |
| `node.discovery.nostr.failure_streak_threshold` | u32 | `5` | Consecutive NAT-traversal failures against a peer before an extended cooldown is applied. At this threshold the daemon also actively re-fetches the peer's advert from `advert_relays` to evict cache entries for peers that have gone away |
| `node.discovery.nostr.extended_cooldown_secs` | u64 | `1800` | Cooldown applied to a peer once `failure_streak_threshold` is hit. Suppresses both open-discovery sweep enqueues and per-attempt retry firings until elapsed (30 minutes default) |
| `node.discovery.nostr.warn_log_interval_secs` | u64 | `300` | Minimum interval between `NAT traversal failed` WARN log lines for the same peer. Subsequent failures inside the window log at DEBUG to reduce log spam on public-test nodes with many cache-learned peers |
| `node.discovery.nostr.failure_state_max_entries` | usize | `4096` | Maximum entries retained in the per-npub failure-state map. Bounds memory under high cache turnover; oldest entries (by last failure time) are evicted when the cap is exceeded |
| `node.discovery.nostr.protocol_mismatch_cooldown_secs` | u64 | `86400` | Cooldown applied after observing a fatal protocol mismatch on a Nostr-adopted bootstrap transport (e.g. `Unknown FMP version` from a peer running a different FMP-protocol version). Independent of `extended_cooldown_secs` and much longer (24 hours default) because the mismatch is structural — re-traversing is wasted effort until one side upgrades |

If `stun_servers` is omitted, the built-in default list above is used. If it is
specified in YAML, the configured list fully overrides the defaults.
Initiators use only this local list for outbound STUN queries; peer-advertised
STUN values are published for diagnostics/interoperability but are not used as
arbitrary egress targets.
The built-in advert and DM relay defaults point at widely-operated public
relays (Damus, nos.lol, Primal) as best-effort endpoints; operators are
encouraged to override them with their own relay preferences for production
deployments.
Advert freshness is enforced semantically: events with expired NIP-40
`expiration` tags are dropped, and adverts are also bounded by a created-at
staleness window derived from `advert_ttl_secs` (with a grace multiplier).
The current in-tree STUN parser handles IPv4 and IPv6 mapped-address
attributes. Local traversal candidates include active non-loopback private
interface addresses (RFC1918 IPv4 and IPv6 ULA) plus probed local egress
addresses for the punch socket port.
During punching, compatible private-subnet candidates and reflexive candidates
are attempted in parallel; the first successful path wins.

#### LAN Discovery (`node.discovery.lan.*`)

Peer discovery on the local link via mDNS / DNS-SD (RFC 6762 / RFC
6763). When enabled, the node publishes a `_fips._udp.local.` service
advert carrying its `npub` (and optional scope) and concurrently
browses for the same service type to learn same-broadcast-domain peers.
The result is sub-second peer pairing with no Nostr-relay roundtrip,
STUN observation, or NAT traversal: the observed endpoint is by
construction routable from the consumer's LAN.

mDNS adverts are unauthenticated, so a LAN advert is treated only as a
routing hint. Identity is still proven end-to-end by the Noise XX
handshake the node initiates against the observed endpoint; a spoofed
advert carrying another peer's npub fails the handshake and is dropped.
LAN discovery requires an active UDP transport (peers dial the
advertised UDP port to begin the handshake).

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.discovery.lan.enabled` | bool | `false` | Master switch. Opt-in: enable for sub-second same-LAN pairing. Default-off avoids reintroducing a per-LAN identity broadcast on nodes that have deliberately disabled other discovery channels |
| `node.discovery.lan.service_type` | string | `"_fips._udp.local."` | DNS-SD service type. Primarily an override for integration tests running multiple isolated services on one loopback interface; leave at the default in production |
| `node.discovery.lan.scope` | string | *(none)* | Optional application/network scope carried in a `scope=<name>` TXT entry. Browsers with a scope set only surface peers advertising the same scope, so nodes on the same physical LAN configured for different mesh networks do not cross-feed. Intentionally separate from `node.discovery.nostr.app` so relay-visible adverts can stay generic while LAN discovery is isolated per private network |

### Spanning Tree (`node.tree.*`)

Controls tree construction and parent selection.

| Parameter                              | Type  | Default | Description                                      |
|----------------------------------------|-------|---------|--------------------------------------------------|
| `node.tree.announce_min_interval_ms`   | u64   | `500`   | Per-peer TreeAnnounce rate limit                 |
| `node.tree.parent_hysteresis`          | f64   | `0.2`   | Cost improvement fraction required for same-root parent switch (0.0–1.0) |
| `node.tree.hold_down_secs`             | u64   | `30`    | Suppress non-mandatory re-evaluation after parent switch |
| `node.tree.reeval_interval_secs`       | u64   | `60`    | Periodic cost-based parent re-evaluation interval (0 = disabled) |
| `node.tree.flap_threshold`             | u32   | `4`     | Parent switches in window before dampening engages  |
| `node.tree.flap_window_secs`           | u64   | `60`    | Sliding window for counting parent switches          |
| `node.tree.flap_dampening_secs`        | u64   | `120`   | Extended hold-down duration when flap threshold exceeded |

### Bloom Filter (`node.bloom.*`)

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.bloom.update_debounce_ms` | u64 | `500` | Debounce interval for filter update propagation |
| `node.bloom.max_inbound_fpr` | f64 | `0.20` | Antipoison cap: reject inbound `FilterAnnounce` frames whose advertised false-positive rate exceeds this value. Valid range `(0.0, 1.0)`. The default `0.20` corresponds to fill 0.7248 at k=5 (≈2,114 entries on the 1 KB filter); a saturated/poisoned filter is still ~100% FPR and rejected |

Bloom filter size (1 KB), hash count (5), and size classes are protocol
constants and not configurable.

### ECN Signaling (`node.ecn.*`)

Controls hop-by-hop ECN (Explicit Congestion Notification) signaling. When
enabled, transit nodes detect congestion on outgoing links (via MMP loss/ETX
metrics or kernel buffer drops) and set the CE flag on forwarded FMP frames.
Destination nodes mark ECN-capable IPv6 packets with CE before TUN delivery
per RFC 3168, enabling end-host TCP congestion control to react.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.ecn.enabled` | bool | `true` | Enable ECN congestion signaling (CE flag relay and local congestion detection) |
| `node.ecn.loss_threshold` | f64 | `0.05` | MMP loss rate threshold for CE marking (0.0–1.0). When the outgoing link's loss rate meets or exceeds this value, forwarded packets are CE-marked. |
| `node.ecn.etx_threshold` | f64 | `3.0` | MMP ETX threshold for CE marking (≥1.0). When the outgoing link's ETX meets or exceeds this value, forwarded packets are CE-marked. |

Congestion detection triggers on any of: outgoing link loss ≥ `loss_threshold`,
outgoing link ETX ≥ `etx_threshold`, or kernel receive buffer drops detected on
any local transport. CE is relayed hop-by-hop: once set on any hop, the flag
stays set for all subsequent hops to the destination.

### Rekey (`node.rekey.*`)

Controls periodic Noise rekey for forward secrecy. When enabled, both FMP
(link-layer IK) and FSP (session-layer XK) sessions perform fresh Diffie-Hellman
key exchanges after a time or message count threshold, whichever comes first.
A 10-second drain window keeps the old session active for decryption during
cutover.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.rekey.enabled` | bool | `true` | Enable periodic Noise rekey on all links and sessions |
| `node.rekey.after_secs` | u64 | `120` | Initiate rekey after this many seconds on a session |
| `node.rekey.after_messages` | u64 | `65536` | Initiate rekey after this many messages sent on a session |

### Session / Data Plane (`node.session.*`)

Controls end-to-end session behavior and packet queuing.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.session.default_ttl` | u8 | `64` | Default SessionDatagram TTL |
| `node.session.pending_packets_per_dest` | usize | `16` | Queue depth per destination during session establishment |
| `node.session.pending_max_destinations` | usize | `256` | Max destinations with pending packets |
| `node.session.idle_timeout_secs` | u64 | `90` | Idle session timeout; established sessions with no application data for this duration are removed. MMP reports (SenderReport, ReceiverReport, PathMtuNotification) do not count as activity |
| `node.session.coords_warmup_packets` | u8 | `5` | Number of initial data packets per session that include the CP flag for transit cache warmup; also the reset count on CoordsRequired/PathBroken receipt |
| `node.session.coords_response_interval_ms` | u64 | `2000` | Minimum interval (ms) between standalone CoordsWarmup responses to CoordsRequired/PathBroken signals per destination |

The anti-replay window size (2048 packets) is a compile-time constant and not
configurable.

### Link-Layer MMP (`node.mmp.*`)

Metrics Measurement Protocol for per-peer link measurement. See
[../design/fips-mesh-layer.md](../design/fips-mesh-layer.md) for behavioral details.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.mmp.mode` | string | `"full"` | Operating mode: `full` (sender + receiver reports), `lightweight` (receiver reports only), or `minimal` (spin bit + CE echo only, no reports) |
| `node.mmp.log_interval_secs` | u64 | `30` | Periodic operator log interval for link metrics |
| `node.mmp.owd_window_size` | usize | `32` | One-way delay trend ring buffer size |

### Session-Layer MMP (`node.session_mmp.*`)

Metrics Measurement Protocol for end-to-end session measurement. Configured
independently from link-layer MMP because session reports are routed through
every transit link, consuming bandwidth proportional to path length.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.session_mmp.mode` | string | `"full"` | Operating mode: `full`, `lightweight`, or `minimal` |
| `node.session_mmp.log_interval_secs` | u64 | `30` | Periodic operator log interval for session metrics |
| `node.session_mmp.owd_window_size` | usize | `32` | One-way delay trend ring buffer size |

### Internal Buffers (`node.buffers.*`)

Channel sizes affecting throughput and memory. Primarily useful for performance
tuning under high load or on memory-constrained devices.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `node.buffers.packet_channel` | usize | `1024` | Transport to Node packet channel capacity |
| `node.buffers.tun_channel` | usize | `1024` | TUN to Node outbound channel capacity |
| `node.buffers.dns_channel` | usize | `64` | DNS to Node identity channel capacity |

## TUN Interface (`tun.*`)

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `tun.enabled` | bool | `false` | Enable TUN virtual interface |
| `tun.name` | string | `"fips0"` | Interface name |
| `tun.mtu` | u16 | `1280` | Interface MTU (IPv6 minimum) |

## DNS Responder (`dns.*`)

Resolves `<npub>.fips` queries to FIPS IPv6 addresses. Resolution is pure
computation (npub to public key to address); resolved identities are registered
with the node for routing.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `dns.enabled` | bool | `true` | Enable DNS responder |
| `dns.bind_addr` | string | `"::1"` | Bind address. Default is IPv6 loopback only; the shipped `fips-dns-setup` configures systemd-resolved to forward `.fips` queries to `[::1]:5354`. To expose the responder to mesh peers (or to the gateway over IPv4), override (e.g., `"::"` for all interfaces). |
| `dns.port` | u16 | `5354` | Listen port |
| `dns.ttl` | u32 | `300` | AAAA record TTL in seconds |

The `dns.ttl` value should not exceed `node.cache.coord_ttl_secs` to avoid
stale address mappings.

### Host Mapping

The DNS resolver checks a host map before falling back to direct npub
resolution, enabling names like `gateway.fips` instead of `npub1...fips`.
The host map is populated from two sources:

1. **Peer aliases** — the `alias` field on configured peers in `peers:`.
2. **Hosts file** — `/etc/fips/hosts`, one `hostname npub1...` per line.
   Blank lines and `#` comments are allowed.

On conflict, hosts-file entries take precedence over peer aliases. The
hosts file is auto-reloaded on modification (mtime change) without
restarting the daemon. Hostnames are case-insensitive.

The installer ships `/etc/fips/hosts` pre-populated with the public test
mesh roster (`test-us01` … `test-uk01`). Operator-style guide for
adding entries and the precedence rules:
[../how-to/host-aliases.md](../how-to/host-aliases.md).

## Transports (`transports.*`)

### UDP (`transports.udp.*`)

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `transports.udp.bind_addr` | string | `"0.0.0.0:2121"` | UDP bind address and port. Ignored when `outbound_only: true` (kernel-assigned ephemeral port is used regardless). |
| `transports.udp.mtu` | u16 | `1280` | Transport MTU |
| `transports.udp.recv_buf_size` | usize | `2097152` | UDP socket receive buffer size in bytes (2 MB). Linux kernel doubles the requested value internally. Host `net.core.rmem_max` must be >= this value. |
| `transports.udp.send_buf_size` | usize | `2097152` | UDP socket send buffer size in bytes (2 MB). Host `net.core.wmem_max` must be >= this value. |
| `transports.udp.advertise_on_nostr` | bool | `false` | Include this UDP transport in Nostr endpoint adverts. Implicitly forced false when `outbound_only: true`. |
| `transports.udp.public` | bool | `false` | If advertised: `true` publishes direct `host:port`; `false` publishes `udp:nat` rendezvous |
| `transports.udp.external_addr` | string | *(none)* | Explicit advertise-as override. Bare IP (`"203.0.113.45"` — bind port is appended) or full `host:port`. Takes precedence over the bound address and STUN autodiscovery. Useful when the public IP isn't on a local interface (cloud 1:1 NAT, EIP) or to skip STUN for a deterministic value. |
| `transports.udp.outbound_only` | bool | `false` | Pure-client posture. When `true`, the transport binds to `0.0.0.0:0` (kernel-assigned ephemeral port) regardless of `bind_addr`, refuses inbound handshake msg1, and is never advertised on Nostr regardless of `advertise_on_nostr`. |
| `transports.udp.accept_connections` | bool | `true` | Accept inbound handshake msg1 from new peers. Combine with `outbound_only: false` and `accept_connections: false` (plus `auto_connect` on peer entries) for a node that initiates outbound links but rejects fresh inbound handshakes. The handshake handler carves out msg1 from peers already established on this transport so rekey continues to work. |

### Ethernet (`transports.ethernet.*`)

Ethernet transport sends raw frames via AF_PACKET SOCK_DGRAM sockets.
Requires `CAP_NET_RAW` or running as root. Linux only.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `interface` | string | *(required)* | Network interface name (e.g., `"eth0"`, `"enp3s0"`) |
| `ethertype` | u16 | `0x2121` | EtherType |
| `mtu` | u16 | *(auto)* | Override MTU. Default: interface MTU minus 3 (for frame type + length prefix) |
| `recv_buf_size` | usize | `2097152` | Socket receive buffer size in bytes (2 MB) |
| `send_buf_size` | usize | `2097152` | Socket send buffer size in bytes (2 MB) |
| `discovery` | bool | `true` | Listen for discovery beacons from other nodes |
| `announce` | bool | `false` | Broadcast announcement beacons on the LAN |
| `auto_connect` | bool | `false` | Auto-connect to discovered peers |
| `accept_connections` | bool | `false` | Accept incoming connection attempts from discovered peers |
| `beacon_interval_secs` | u64 | `30` | Announcement beacon interval in seconds (minimum 10) |

**Named instances.** Multiple Ethernet interfaces can be configured by
using named sub-keys instead of flat parameters:

```yaml
transports:
  ethernet:
    lan:
      interface: "eth0"
      discovery: true
      announce: true
    backbone:
      interface: "eth1"
      announce: false
```

Each named instance operates independently with its own socket and
discovery state. The instance name is used in log messages and the
`name()` method on the Transport trait.

### TCP (`transports.tcp.*`)

TCP transport enables firewall traversal on networks that block UDP but
allow TCP (e.g., port 443). Uses FMP header-based framing with zero
overhead.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `transports.tcp.bind_addr` | string | *(none)* | Listen address (e.g., `"0.0.0.0:8443"`). If omitted, outbound-only mode. |
| `transports.tcp.mtu` | u16 | `1400` | Default MTU. Per-connection MTU derived from `TCP_MAXSEG` when available. |
| `transports.tcp.connect_timeout_ms` | u64 | `5000` | Outbound connect timeout in milliseconds |
| `transports.tcp.nodelay` | bool | `true` | `TCP_NODELAY` (disable Nagle for low latency) |
| `transports.tcp.keepalive_secs` | u64 | `30` | TCP keepalive interval in seconds (0 = disabled) |
| `transports.tcp.recv_buf_size` | usize | `2097152` | Socket receive buffer size in bytes (2 MB) |
| `transports.tcp.send_buf_size` | usize | `2097152` | Socket send buffer size in bytes (2 MB) |
| `transports.tcp.max_inbound_connections` | usize | `256` | Maximum simultaneous inbound connections |
| `transports.tcp.advertise_on_nostr` | bool | `false` | Include this TCP transport in Nostr endpoint adverts |
| `transports.tcp.external_addr` | string | *(none)* | Explicit advertise-as override. Bare IP or full `host:port`. **Required** when `bind_addr` is wildcard (e.g. `"0.0.0.0:443"`) and `advertise_on_nostr: true`, since TCP has no STUN equivalent for autodiscovery. Common on cloud 1:1 NAT / EIP setups where the public IP isn't bindable on the host. |

**Named instances.** Like other transports, multiple TCP instances can
be configured with named sub-keys:

```yaml
transports:
  tcp:
    public:
      bind_addr: "0.0.0.0:443"
    internal:
      bind_addr: "10.0.0.1:8443"
      max_inbound_connections: 64
```

### Tor (`transports.tor.*`)

Tor transport routes FIPS traffic through the Tor network for anonymity.
Requires an external Tor daemon providing a SOCKS5 proxy. Three modes:
`socks5` for outbound-only, `control_port` for outbound + monitoring,
`directory` for outbound + inbound via Tor-managed onion service.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `transports.tor.mode` | string | `"socks5"` | Tor access mode: `socks5` (outbound only), `control_port` (outbound + monitoring), or `directory` (outbound + inbound onion service) |
| `transports.tor.socks5_addr` | string | `"127.0.0.1:9050"` | SOCKS5 proxy address (host:port) |
| `transports.tor.connect_timeout_ms` | u64 | `120000` | Connect timeout in milliseconds. Tor circuits take 10–60s. |
| `transports.tor.mtu` | u16 | `1400` | Default MTU |
| `transports.tor.control_addr` | string | `"/run/tor/control"` | Tor control port address: Unix socket path or host:port. Used in `control_port` mode; optional in `directory` mode for monitoring. |
| `transports.tor.control_auth` | string | `"cookie"` | Control port authentication: `"cookie"`, `"cookie:/path/to/cookie"`, or `"password:<secret>"`. |
| `transports.tor.cookie_path` | string | `"/var/run/tor/control.authcookie"` | Path to Tor control cookie file. Used when `control_auth` is `"cookie"`. |
| `transports.tor.max_inbound_connections` | usize | `64` | Maximum inbound connections via onion service. |
| `transports.tor.directory_service.hostname_file` | string | `"/var/lib/tor/fips_onion_service/hostname"` | Path to Tor-managed hostname file containing the `.onion` address. |
| `transports.tor.directory_service.bind_addr` | string | `"127.0.0.1:8443"` | Local bind address for the listener that Tor forwards inbound connections to. Must match `HiddenServicePort` target in `torrc`. |
| `transports.tor.advertised_port` | u16 | `443` | Public-facing onion port published in Nostr overlay adverts. Must match the virtual port in torrc's `HiddenServicePort <port> 127.0.0.1:<bind_port>` directive — that is the port other peers will use to reach this onion. |

**Named instances.** Like other transports, multiple Tor instances can
be configured with named sub-keys for different SOCKS5 proxy endpoints.

**Directory mode** (recommended for production). Tor manages the onion
service via `HiddenServiceDir` in `torrc`. FIPS reads the `.onion`
address from the hostname file and binds a local TCP listener. This
enables Tor's `Sandbox 1` (seccomp-bpf). If `control_addr` is also
set, the transport connects to the control port for daemon monitoring
(non-fatal on failure).

**Control port mode.** Connects to the Tor daemon's control port for
monitoring only (bootstrap status, circuit health, traffic stats).
No inbound connections. Both `control_addr` and `control_auth` are
required.

### UDP + Tor Bridge Example

A node bridging clearnet (UDP) and anonymous (Tor) portions of the mesh:

```yaml
node:
  identity:
    persistent: true

tun:
  enabled: true

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    mtu: 1472
  tor:
    socks5_addr: "127.0.0.1:9050"

peers:
  - npub: "npub1abc..."
    alias: "clearnet-peer"
    addresses:
      - transport: udp
        addr: "203.0.113.5:2121"
  - npub: "npub1def..."
    alias: "anonymous-peer"
    addresses:
      - transport: tor
        addr: "abc123...xyz.onion:2121"
```

### Tor Directory Mode Example

A node accepting inbound connections via Tor-managed onion service
(recommended for production — enables Sandbox 1):

```yaml
node:
  identity:
    persistent: true

tun:
  enabled: true

transports:
  tor:
    mode: "directory"
    socks5_addr: "127.0.0.1:9050"
    control_addr: "/run/tor/control"    # optional, for monitoring
    control_auth: "cookie"
    directory_service:
      hostname_file: "/var/lib/tor/fips/hostname"
      bind_addr: "127.0.0.1:8444"

peers:
  - npub: "npub1abc..."
    alias: "tor-peer"
    addresses:
      - transport: tor
        addr: "abcdef...xyz.onion:8443"
```

Requires a corresponding `torrc`:

```text
HiddenServiceDir /var/lib/tor/fips
HiddenServicePort 8443 127.0.0.1:8444
```

### Nym (`transports.nym.*`)

Nym transport routes FIPS traffic through the Nym mixnet for
metadata-resistant anonymity. Outbound-only: connections are made
through a `nym-socks5-client` SOCKS5 proxy that must be running
separately (e.g. as a service running alongside the fips daemon or as a
container). There is no inbound listener — a Nym-only node initiates
outbound links but is not reachable for unsolicited inbound handshakes.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `transports.nym.socks5_addr` | string | `"127.0.0.1:1080"` | `nym-socks5-client` SOCKS5 proxy address (host:port) |
| `transports.nym.connect_timeout_ms` | u64 | `300000` | Outbound connect timeout in milliseconds. Mixnet SOCKS5 connections traverse 3 mix nodes with timing obfuscation and can take several minutes, so this is generous (300s). |
| `transports.nym.mtu` | u16 | `1400` | Default MTU |
| `transports.nym.startup_timeout_secs` | u64 | `120` | Seconds to wait for `nym-socks5-client` to become ready at startup before giving up |

**Named instances.** Like other transports, multiple Nym instances can
be configured with named sub-keys for different SOCKS5 proxy endpoints.

### BLE (`transports.ble.*`)

Bluetooth Low Energy transport using L2CAP Connection-Oriented Channels.
Linux + glibc only — at build time, `build.rs` probes for the BlueZ /
`bluer` crate dependencies and sets the `bluer_available` `cfg`; the BLE
runtime is gated behind `#[cfg(bluer_available)]`. There is no Cargo
feature flag to toggle. On non-glibc Linux (musl) or non-Linux platforms,
BLE config still parses but the transport runtime is absent and config
entries become no-ops. Communicates with BlueZ via D-Bus through the
`bluer` crate.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `transports.ble.adapter` | string | `"hci0"` | HCI adapter name |
| `transports.ble.psm` | u16 | `0x0085` (133) | L2CAP Protocol/Service Multiplexer |
| `transports.ble.mtu` | u16 | `2048` | Default MTU. Actual MTU is negotiated per-link during L2CAP connection setup. |
| `transports.ble.max_connections` | usize | `7` | Maximum concurrent BLE connections |
| `transports.ble.connect_timeout_ms` | u64 | `10000` | Outbound connect timeout in milliseconds |
| `transports.ble.advertise` | bool | `true` | Broadcast BLE beacon advertisements for peer discovery |
| `transports.ble.scan` | bool | `true` | Listen for BLE beacon advertisements from other nodes |
| `transports.ble.auto_connect` | bool | `false` | Automatically connect to discovered peers |
| `transports.ble.accept_connections` | bool | `true` | Accept incoming L2CAP connections |
| `transports.ble.probe_cooldown_secs` | u64 | `30` | Cooldown before re-probing the same BLE address |

**Address format.** BLE peer addresses use the form
`"adapter/device_address"` — for example, `"hci0/AA:BB:CC:DD:EE:FF"`.

**Advertising and scanning.** When `advertise` is enabled, the transport
advertises the FIPS service UUID continuously so that nearby nodes can
discover and connect via L2CAP. When `scan` is enabled, the transport
continuously scans for other FIPS nodes' advertisements. Discovered
peers are probed immediately (L2CAP connect + pubkey exchange) with a
cooldown (`probe_cooldown_secs`) to prevent rapid re-probing of the same
address. If two nodes probe each other at the same time (cross-probe),
a deterministic tie-breaker based on NodeAddr comparison ensures only
one connection is established.

**Connection pool.** The `max_connections` parameter limits the number of
concurrent BLE connections. When the pool is full, the least-recently-used
connection is evicted to make room for new connections.

### BLE Example

A node using BLE for local mesh discovery alongside UDP for internet peers:

```yaml
node:
  identity:
    persistent: true

tun:
  enabled: true

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
  ble:
    adapter: "hci0"
    advertise: true
    scan: true
    auto_connect: true
    accept_connections: true

peers:
  - npub: "npub1abc..."
    alias: "internet-peer"
    addresses:
      - transport: udp
        addr: "203.0.113.5:2121"
    connect_policy: auto_connect
```

BLE peers on the local radio range are discovered automatically via
beacons — no static peer entries needed. Internet peers still require
explicit configuration.

## Peers (`peers[]`)

Static peer list. Each entry defines a peer to connect to.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `peers[].npub` | string | *(required)* | Peer's Nostr public key (npub-encoded) |
| `peers[].alias` | string | *(none)* | Human-readable name for logging |
| `peers[].addresses` | list | `[]` | Transport addresses for the peer. May be left empty (or omitted) when `via_nostr: true`, in which case the daemon resolves endpoints from the peer's Nostr advert at dial time. |
| `peers[].addresses[].transport` | string | *(required)* | Transport type: `udp`, `tcp`, `ethernet`, `tor`, or `ble` |
| `peers[].addresses[].addr` | string | *(required)* | Transport address. UDP/TCP: `"host:port"` (IP or DNS hostname). Ethernet: `"interface/mac"` (e.g., `"eth0/aa:bb:cc:dd:ee:ff"`). BLE: `"adapter/device_address"` (e.g., `"hci0/AA:BB:CC:DD:EE:FF"`). Tor: `".onion:port"` or `"host:port"` |
| `peers[].addresses[].priority` | u8 | `100` | Address priority (lower = preferred) |
| `peers[].connect_policy` | string | `"auto_connect"` | Connection policy: `auto_connect`, `on_demand`, or `manual`. Note: `on_demand` and `manual` are reserved for future use; the only policy currently honored at runtime is `auto_connect`. |
| `peers[].auto_reconnect` | bool | `true` | Automatically reconnect after MMP link-dead removal (exponential backoff, unlimited retries) |
| `peers[].via_nostr` | bool | `false` | Append Nostr advert-derived endpoints after static addresses for this peer |

## Gateway (`gateway.*`)

The `gateway.*` block configures the optional `fips-gateway`
service, which lets unmodified LAN hosts reach mesh destinations
through DNS proxy + virtual-IP NAT (and, optionally, exposes
LAN-side services back into the mesh through inbound port forwards).
The gateway is a separate service from the FIPS daemon but reads the
same `fips.yaml` file. The block is read only when `fips-gateway` is
running; the `fips` daemon ignores it. Linux only — the field is
gated behind `#[cfg(target_os = "linux")]`. For setup, see
[../how-to/deploy-gateway.md](../how-to/deploy-gateway.md); for the
end-to-end design, see
[../design/fips-gateway.md](../design/fips-gateway.md).

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `gateway.enabled` | bool | `false` | Enable the gateway. Must be `true` for `fips-gateway` to start. |
| `gateway.pool` | string | *(required)* | Virtual IPv6 pool CIDR (e.g., `"fd01::/112"`). Must not overlap with the FIPS mesh address space (`fd00::/8`) or any address space already in use on the LAN. The `/112` size yields 65 536 virtual IPs, which is the gateway's hard cap regardless of CIDR width. |
| `gateway.lan_interface` | string | *(required)* | LAN-facing network interface name (e.g., `"enp3s0"`). Used for proxy-NDP entry installation so LAN clients can resolve the link-layer address of allocated virtual IPs. |
| `gateway.pool_grace_period` | u64 | `60` | Seconds a virtual-IP allocation is retained after its last referencing session ends, before the address is returned to the free pool. Larger values reduce churn for short-lived flows; smaller values reclaim addresses faster. |

### Gateway DNS (`gateway.dns.*`)

Settings for the gateway's DNS listener and its upstream link to the
FIPS daemon's `.fips` resolver. The gateway proxies `.fips` queries to
the daemon's resolver, which returns mesh addresses; the gateway then
allocates a virtual IP from the pool and rewrites the response.
Non-`.fips` queries are answered with `REFUSED`.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `gateway.dns.listen` | string | `"[::1]:5353"` | DNS listen address. The default binds IPv6 loopback on an unprivileged port, matching the canonical deployment where another resolver on the host (dnsmasq, systemd-resolved, BIND) holds port 53 and forwards `.fips` queries to the gateway over loopback. Bind on the LAN-side IP (e.g., `"192.168.1.1:53"`) or wildcard (`"[::]:53"`) only on hosts with no other resolver on 53 and where LAN clients query the gateway directly. See [../how-to/troubleshoot-gateway.md](../how-to/troubleshoot-gateway.md). |
| `gateway.dns.upstream` | string | `"[::1]:5354"` | Upstream FIPS daemon resolver. **Must match the daemon's `dns.bind_addr` and `dns.port`.** Defaults match the daemon defaults (`::1:5354`). A v4 upstream (`"127.0.0.1:5354"`) cannot reach a daemon bound on `[::1]:5354` — Linux IPv6 sockets bound to explicit `::1` do not accept v4-mapped traffic. If you change the daemon's `dns.bind_addr`, update this field accordingly. |
| `gateway.dns.ttl` | u32 | `60` | TTL in seconds on AAAA responses returned to LAN clients. Smaller values let the gateway recycle pool addresses faster; larger values reduce LAN-side query traffic. |

### Conntrack (`gateway.conntrack.*`)

Linux conntrack timeout overrides for the gateway's NAT table. These
adjust the kernel-default timeouts for NAT sessions installed by the
gateway. All values are in seconds; omit any field to inherit the
gateway's built-in default (which itself usually matches the kernel
default for that protocol).

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `gateway.conntrack.tcp_established` | u64 | `432000` | TCP established-state timeout (5 days). Long-lived TCP flows (SSH, persistent HTTP) keep their NAT mapping alive for at least this long without traffic. |
| `gateway.conntrack.udp_timeout` | u64 | `30` | UDP unreplied timeout. Applied until reply traffic is observed in the reverse direction. |
| `gateway.conntrack.udp_assured` | u64 | `180` | UDP assured (bidirectional) timeout. Applied once reply traffic has been observed. |
| `gateway.conntrack.icmp_timeout` | u64 | `30` | ICMP echo / error timeout. |

### Inbound Port Forwards (`gateway.port_forwards[]`)

Optional list of inbound port-forward rules. Each rule maps a TCP or
UDP port on the gateway's `fips0` mesh-side address to a `host:port`
on the LAN. Mesh peers connect to the gateway's mesh address on the
listen port; the gateway terminates the connection and forwards the
payload to the LAN target. This is the inverse of the outbound mode:
the LAN service is exposed to the mesh, not the other way around. See
[../how-to/deploy-gateway.md](../how-to/deploy-gateway.md) for the
operator recipe.

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `gateway.port_forwards[].listen_port` | u16 | *(required)* | Port on `fips0` that mesh peers connect to. Must be non-zero. The `(listen_port, proto)` pair must be unique across the list. |
| `gateway.port_forwards[].proto` | string | *(required)* | Transport protocol: `tcp` or `udp`. |
| `gateway.port_forwards[].target` | string | *(required)* | LAN destination as IPv6 `[addr]:port` (e.g., `"[fd12:3456::10]:80"`). IPv4 targets are rejected at config-load time. |

### Gateway Example

A typical gateway with both outbound (LAN-to-mesh) and inbound
(mesh-to-LAN) modes enabled:

```yaml
gateway:
  enabled: true
  pool: "fd01::/112"
  lan_interface: "enp3s0"
  dns:
    listen: "[::1]:5353"
    upstream: "[::1]:5354"
    ttl: 60
  pool_grace_period: 60
  conntrack:
    tcp_established: 432000
    udp_assured: 180
  port_forwards:
    - listen_port: 8080
      proto: tcp
      target: "[fd12:3456::10]:80"
    - listen_port: 5353
      proto: udp
      target: "[fd12:3456::10]:53"
```

## Minimal Example

A typical node configuration enabling TUN, DNS, and a single peer:

```yaml
node:
  identity:
    nsec: "0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f20"

tun:
  enabled: true
  name: fips0
  mtu: 1280

dns:
  enabled: true
  bind_addr: "127.0.0.1"
  port: 53

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    mtu: 1472

peers:
  - npub: "npub1tdwa4vjrjl33pcjdpf2t4p027nl86xrx24g4d3avg4vwvayr3g8qhd84le"
    alias: "node-b"
    addresses:
      - transport: udp
        addr: "172.20.0.11:2121"
    connect_policy: auto_connect
```

### Mixed UDP + Ethernet Example

A node bridging internet peers (UDP) and a local Ethernet segment with
beacon discovery:

```yaml
node:
  identity:
    nsec: "0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f20"

tun:
  enabled: true

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    mtu: 1472
  ethernet:
    interface: "eth0"
    discovery: true
    announce: true
    auto_connect: true
    accept_connections: true

peers:
  - npub: "npub1tdwa4vjrjl33pcjdpf2t4p027nl86xrx24g4d3avg4vwvayr3g8qhd84le"
    alias: "internet-peer"
    addresses:
      - transport: udp
        addr: "203.0.113.5:2121"
    connect_policy: auto_connect
```

Ethernet peers on the local segment are discovered automatically via
beacons — no static peer entries needed. Internet peers still require
explicit configuration.

All `node.*` parameters use their defaults. To override specific values, add
only the relevant sections:

```yaml
node:
  identity:
    nsec: "..."
  limits:
    max_peers: 64
  retry:
    max_retries: 10
    max_backoff_secs: 600
  cache:
    coord_size: 100000
```

## Complete Reference

The full YAML structure with all defaults:

```yaml
node:
  identity:
    nsec: null                       # secret key in nsec or hex (null = depends on persistent)
    persistent: false                # true = load/save fips.key; false = ephemeral each start
  leaf_only: false
  tick_interval_secs: 1
  base_rtt_ms: 100
  heartbeat_interval_secs: 10
  link_dead_timeout_secs: 30
  limits:
    max_connections: 256
    max_peers: 128
    max_links: 256
    max_pending_inbound: 1000
  rate_limit:
    handshake_burst: 100
    handshake_rate: 10.0
    handshake_timeout_secs: 30
    handshake_resend_interval_ms: 1000
    handshake_resend_backoff: 2.0
    handshake_max_resends: 5
  retry:
    max_retries: 5
    base_interval_secs: 5
    max_backoff_secs: 300
  cache:
    coord_size: 50000
    coord_ttl_secs: 300
    identity_size: 10000
  discovery:
    ttl: 64
    attempt_timeouts_secs: [1, 2, 4, 8]
    recent_expiry_secs: 10
    backoff_base_secs: 0
    backoff_max_secs: 0
    forward_min_interval_secs: 2
    # lan:                             # uncomment to enable mDNS LAN discovery
    #   enabled: true                  # opt-in, default false
    #   scope: "my-mesh"               # optional per-network scope filter
  tree:
    announce_min_interval_ms: 500
    parent_hysteresis: 0.2              # cost improvement fraction for parent switch
    hold_down_secs: 30                  # suppress re-evaluation after switch
    reeval_interval_secs: 60            # periodic cost-based re-evaluation (0 = disabled)
    flap_threshold: 4                    # parent switches before dampening
    flap_window_secs: 60                 # sliding window for flap detection
    flap_dampening_secs: 120             # extended hold-down on flap
  bloom:
    update_debounce_ms: 500
    max_inbound_fpr: 0.20            # antipoison cap on inbound FilterAnnounce FPR
  session:
    default_ttl: 64
    pending_packets_per_dest: 16
    pending_max_destinations: 256
    idle_timeout_secs: 90
    coords_warmup_packets: 5
    coords_response_interval_ms: 2000
  mmp:
    mode: full                       # full | lightweight | minimal
    log_interval_secs: 30
    owd_window_size: 32
  session_mmp:
    mode: full                       # full | lightweight | minimal
    log_interval_secs: 30
    owd_window_size: 32
  ecn:
    enabled: true                    # ECN congestion signaling (CE flag relay)
    loss_threshold: 0.05             # MMP loss rate threshold for CE marking (5%)
    etx_threshold: 3.0               # MMP ETX threshold for CE marking
  rekey:
    enabled: true                    # periodic Noise rekey for forward secrecy
    after_secs: 120                  # rekey interval (seconds)
    after_messages: 65536            # rekey after N messages sent
  control:
    enabled: true
    socket_path: null                # null = auto ($XDG_RUNTIME_DIR → /run/fips → /tmp fallback)
  buffers:
    packet_channel: 1024
    tun_channel: 1024
    dns_channel: 64

tun:
  enabled: false
  name: "fips0"
  mtu: 1280

dns:
  enabled: true
  bind_addr: "::1"
  port: 5354
  ttl: 300

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    mtu: 1280
    recv_buf_size: 2097152           # 2 MB (kernel doubles to 4 MB actual)
    send_buf_size: 2097152           # 2 MB
  # ethernet:                        # uncomment to enable (requires CAP_NET_RAW)
  #   interface: "eth0"              # required: network interface name
  #   ethertype: 0x2121              # default EtherType
  #   mtu: null                      # null = interface MTU - 3 (typically 1497)
  #   recv_buf_size: 2097152         # 2 MB
  #   send_buf_size: 2097152         # 2 MB
  #   discovery: true                # listen for beacons
  #   announce: false                # broadcast beacons
  #   auto_connect: false            # connect to discovered peers
  #   accept_connections: false      # accept inbound handshakes
  #   beacon_interval_secs: 30       # beacon interval (min 10)
  # tcp:                             # uncomment to enable TCP transport
  #   bind_addr: "0.0.0.0:8443"     # listen address (omit for outbound-only)
  #   mtu: 1400                      # default MTU
  #   connect_timeout_ms: 5000       # outbound connect timeout
  #   nodelay: true                  # TCP_NODELAY
  #   keepalive_secs: 30             # keepalive interval (0 = disabled)
  #   recv_buf_size: 2097152         # 2 MB
  #   send_buf_size: 2097152         # 2 MB
  #   max_inbound_connections: 256   # resource protection limit
  # tor:                             # uncomment to enable Tor transport
  #   mode: "socks5"                 # "socks5", "control_port", or "directory"
  #   socks5_addr: "127.0.0.1:9050" # SOCKS5 proxy address
  #   connect_timeout_ms: 120000    # connect timeout (120s for Tor circuits)
  #   mtu: 1400                     # default MTU
  #   # monitoring (control_port mode, or optional in directory mode):
  #   # control_addr: "/run/tor/control"   # Unix socket or host:port
  #   # control_auth: "cookie"             # "cookie" or "password:<secret>"
  #   # cookie_path: "/var/run/tor/control.authcookie"
  #   # directory mode (inbound via Tor-managed onion service):
  #   # directory_service:
  #   #   hostname_file: "/var/lib/tor/fips_onion_service/hostname"
  #   #   bind_addr: "127.0.0.1:8443"
  #   # max_inbound_connections: 64
  #   # advertised_port: 443           # public-facing onion port for Nostr adverts
  # nym:                              # uncomment to enable Nym mixnet transport (outbound-only)
  #   socks5_addr: "127.0.0.1:1080" # nym-socks5-client SOCKS5 proxy address
  #   connect_timeout_ms: 300000    # connect timeout (300s for mixnet)
  #   mtu: 1400                     # default MTU
  #   startup_timeout_secs: 120     # wait for nym-socks5-client to be ready
  # ble:                              # uncomment to enable BLE transport (Linux only, requires BlueZ)
  #   adapter: "hci0"                 # HCI adapter name
  #   psm: 0x0085                     # L2CAP PSM (133)
  #   mtu: 2048                       # default MTU (negotiated per-link)
  #   max_connections: 7              # max concurrent BLE connections
  #   connect_timeout_ms: 10000       # outbound connect timeout
  #   advertise: true                 # broadcast BLE beacons
  #   scan: true                      # listen for BLE beacons
  #   auto_connect: false             # connect to discovered peers
  #   accept_connections: true         # accept incoming L2CAP connections
  #   probe_cooldown_secs: 30         # cooldown before re-probing same address

peers:                               # static peer list
  # - npub: "npub1..."
  #   alias: "node-b"
  #   addresses:
  #     - transport: udp
  #       addr: "10.0.0.2:2121"
  #       priority: 100
  #   connect_policy: auto_connect
  #   auto_reconnect: true           # reconnect after link-dead removal
```
