fips/docs/how-to/enable-nostr-discovery.md

Enable Nostr-Mediated Discovery and NAT Traversal

Nostr-mediated discovery lets FIPS nodes find each other (and punch through UDP NAT) using public Nostr relays as the signaling channel. The feature ships in every stock packaging artifact but is off by default — it activates when an operator sets node.discovery.nostr.enabled: true. Default relay and STUN-server lists ship in the config; both are optional overrides. See ../design/fips-nostr-discovery.md for the design and rationale; see ../reference/configuration.md for the full knob inventory.

Nostr discovery provides three independent capabilities. They can be enabled separately; most deployments end up using two or three of them together.

1. Resolve a known peer's address by npub. Your daemon consumes adverts from the relays to look up the current network endpoint for a peer you have configured by npub. You don't have to know their IP / port / transport in advance.
2. Publish your own endpoint so others can resolve you. Your daemon publishes a signed advert listing the transports it will accept connections on. Has two sub-shapes depending on your network topology: UDP (using NAT traversal if needed) or TCP. Running a Tor onion service is a separate deployment mode, covered in its own section below.
3. Discover peers without prior configuration. Your daemon subscribes to all adverts on a chosen application namespace and treats any publisher as a connection candidate. The most permissive posture; useful for ambient mesh participation.

Each capability is covered below as one or more scenarios with the minimal YAML fragment that enables it. Only keys relevant to Nostr discovery are shown; surrounding node, transport, TUN, DNS, and peer configuration follows the usual shape.

All scenarios assume node.identity is set to a persistent key — an ephemeral identity would invalidate any advert the moment the node restarts. See persistent-identity.md for the persistent-key setup.

For hand-held walkthroughs of each capability, see the resolve-peers-via-nostr, advertise-your-node, and open-discovery tutorials.

Capability 1: Resolve a known peer's address by npub

The node does not publish any advert of its own. It only consumes adverts for peers it has explicitly listed with via_nostr: true. This is the right shape for a client that wants Nostr-mediated resolution without becoming a rendezvous target itself.

node:
  identity:
    persistent: true
  discovery:
    nostr:
      enabled: true
      advertise: false
      policy: configured_only

transports:
  udp:
    bind_addr: "0.0.0.0:2121"

peers:
  - npub: "npub1peer..."
    alias: "remote-node"
    via_nostr: true
    connect_policy: auto_connect

What this achieves: dial endpoints for this peer are taken from the peer's published Nostr advert. configured_only is the default — it is shown here for clarity.

Note: You can also supply a static address alongside via_nostr: true (for example, while testing, or as a known-good fallback if the advert is stale). Add an addresses block to the peer entry; static addresses are tried first on dial and Nostr-resolved endpoints are appended as additional candidates.

Capability 2: Publish your own endpoint so others can resolve you

This capability has three sub-scenarios depending on the network shape your node sits behind.

Sub-scenario 2a: UDP (using NAT traversal if needed)

The node has a public IP (or a stable port-forward) and binds UDP on a known port. It publishes udp:host:port to the advert relays. Any peer that knows this node's npub and has Nostr discovery enabled can dial it without knowing the address out-of-band.

When UDP is wildcard-bound (0.0.0.0:2121, the default), the daemon needs help knowing what IP to put in the advert. There are two ways: STUN auto-discovery (public: true) or an explicit override (external_addr). Both are first-class options; pick the one that fits the deployment.

node:
  identity:
    persistent: true
  discovery:
    nostr:
      enabled: true
      advertise: true

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    advertise_on_nostr: true
    public: true                  # ← STUN auto-discovery

Or, when the public IP is known up front (static residential IP, cloud Elastic IP behind 1:1 NAT, etc.):

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    advertise_on_nostr: true
    public: true                         # ← required, master switch
    external_addr: "203.0.113.45:2121"   # ← explicit address

external_addr accepts a bare IP (combined with the bind port) or a full host:port. public: true is the master switch that gates UDP advertisement; inside that branch, the daemon picks the advertised address in precedence order: explicit external_addr (no STUN observation), a non-wildcard bind_addr, or STUN auto-discovery. Setting external_addr alongside public: true skips STUN entirely — there is no logging cross-check. If UDP is bound directly to a public IP rather than to a wildcard, neither external_addr nor STUN is needed — but advertise_on_nostr: true and public: true are still both required for the daemon to publish the endpoint.

What this achieves: the node publishes a single udp:<public-ip>:2121 endpoint to the three default advert relays (wss://relay.damus.io, wss://nos.lol, wss://offchain.pub).

What the other side needs: either a static addresses entry for this peer, or a peer entry with via_nostr: true and an empty (or omitted) addresses list — the advert-resolved endpoint will be used at dial time. Static and Nostr-resolved addresses can also be combined: when both are present, static addresses are tried first and Nostr-resolved endpoints are appended as fallback.

When the node is behind NAT

If this node doesn't have a stable public UDP endpoint, advertise udp:nat. The daemon runs the STUN + offer/answer exchange with the peer and punches through the NAT to establish a direct UDP link. The peer can either have a public endpoint of its own or also be behind NAT — both shapes work, as long as at least one side has a NAT type compatible with hole-punching.

node:
  identity:
    persistent: true
  discovery:
    nostr:
      enabled: true
      advertise: true
      dm_relays:                       # overrides the default three-relay
        - "wss://relay.damus.io"        # set with two for demonstration;
        - "wss://nos.lol"               # omit this block to keep the defaults
      stun_servers:
        - "stun:stun.l.google.com:19302"
        - "stun:stun.cloudflare.com:3478"

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    advertise_on_nostr: true
    public: false

peers:
  - npub: "npub1peer..."
    alias: "nat-peer"
    addresses:
      - transport: udp
        addr: "nat"
    via_nostr: true
    connect_policy: auto_connect

What this achieves: the node publishes a udp:nat endpoint plus its signaling relays in the advert. When either side initiates, an encrypted offer is sealed to the peer's npub, a matching answer comes back, and both sides punch at the negotiated time. On success, the punch socket is adopted as an FMP UDP transport and Noise IK proceeds normally.

Validation: advertise_on_nostr: true with public: false on UDP requires dm_relays and stun_servers to be non-empty. Both ship with non-empty defaults (three relays and three STUN servers respectively), so the default config passes. The node fails startup only if the operator has explicitly emptied either list — a udp:nat advert without signaling relays or STUN servers is unreachable by construction.

Hole-punching is best-effort. It works reliably when both sides are full-cone or port-restricted NATs. Symmetric NAT on either side typically defeats the punch — the public port a peer sees varies per remote endpoint, so the address learned via STUN does not match the mapping the peer actually needs. The punch attempt times out after punch_duration_ms. udp:nat is the only NAT-traversal mechanism in FIPS; when it can't succeed, there's no in-protocol substitute. Being reachable then becomes a deployment-prerequisite question rather than a transport question — a publicly reachable port (UDP or TCP — both require the same kind of network resource) published as a direct advert per Sub-scenario 2a or 2b.

Sub-scenario 2b: TCP

The node has a public IP (or a stable port-forward) and accepts inbound TCP. It publishes tcp:host:port to the advert relays.

TCP endpoints exist to serve peers whose networks filter outbound UDP (corporate LANs, restrictive guest WiFi). NAT traversal does not apply: the publishing node is publicly reachable on TCP, and the dialing peer's network only needs to permit outbound TCP to the advertised port.

node:
  identity:
    persistent: true
  discovery:
    nostr:
      enabled: true
      advertise: true

transports:
  tcp:
    bind_addr: "0.0.0.0:8443"
    advertise_on_nostr: true
    external_addr: "203.0.113.45:8443"

external_addr is typically required on cloud setups (AWS Elastic IP, etc.) where binding directly to the public IP returns EADDRNOTAVAIL. When TCP is bound directly to a public IP, the override is unnecessary.

What this achieves: the node publishes a tcp:<public-ip>:8443 endpoint to the advert relays. Peers with Nostr discovery enabled dial by npub without out-of-band address exchange.

Tor onion node

A separate deployment mode for nodes that want anonymity and censorship-resistance properties on the data plane. Functionally this still uses Capability 2 (publishing an endpoint to advert relays) — the difference is that the published endpoint is a Tor hidden service rather than a public IP.

The node runs a Tor onion service in directory mode (Tor-managed HiddenServiceDir) and advertises the .onion address. Peers dial via their local Tor SOCKS5 proxy without ever knowing the onion string out-of-band. For the Tor daemon side of this setup, including the inbound-mode trade-offs and the torrc directives each requires, see deploy-tor-onion.md.

node:
  identity:
    persistent: true
  discovery:
    nostr:
      enabled: true
      advertise: true

transports:
  tor:
    mode: directory
    socks5_addr: "127.0.0.1:9050"
    advertised_port: 8443
    directory_service:
      hostname_file: "/var/lib/tor/fips/hostname"
      bind_addr: "127.0.0.1:8444"
    advertise_on_nostr: true

What this achieves: the node publishes a tor:<hash>.onion:8443 endpoint alongside any other advertised transports. The advert itself is still published over clearnet WebSocket relays — Tor protects the data plane, not the discovery plane. See the security and threat model section in ../design/fips-nostr-discovery.md for the trade-off and how to route relay traffic through Tor as well.

Capability 3: Discover peers without prior configuration

Under policy: open, any node that publishes an advert under the same app namespace becomes a candidate. Discovered peers are queued for connection attempts subject to open_discovery_max_pending.

node:
  identity:
    persistent: true
  discovery:
    nostr:
      enabled: true
      advertise: true
      policy: open
      open_discovery_max_pending: 64
      app: "my-experiment.v1"

transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    advertise_on_nostr: true
    public: true

peers: []

What this achieves: peers are discovered entirely through ambient advert traffic on the configured relays. Setting a non-default app value (replacing fips-overlay-v1) scopes the discovery set to participants who opt into the same experiment and avoids being joined to unrelated overlays that happen to share the default namespace.

Scope warning: Open discovery is an admission-free mode. Any node that publishes on the same app name and passes the peer-ACL check becomes a connection candidate. If you rely on peer ACLs for admission control, verify that list is set correctly before enabling this mode. See ../reference/security.md for the peer ACL format.

See also

• ../tutorials/resolve-peers-via-nostr.md — hand-held walkthrough of capability 1
• ../tutorials/advertise-your-node.md — hand-held walkthrough of capability 2 (publish, plus a short section on udp:nat NAT traversal)
• ../tutorials/open-discovery.md — hand-held walkthrough of capability 3 (open ambient discovery, the additive policy: open mode)
• ../design/fips-nostr-discovery.md — discovery runtime design, security model
• ../reference/configuration.md — full node.discovery.nostr.* and per-transport advertise_on_nostr/public table
• ../reference/nostr-events.md — Kind 37195 advert format, Kind 21059 traversal signaling, Kind 10050 inbox relay list
• deploy-tor-onion.md — Tor daemon-side setup for advertising onion endpoints