# Advertise Your Node on Nostr

After
[resolve-peers-via-nostr](resolve-peers-via-nostr.md) your
daemon can look up a peer's current endpoint by npub. This
tutorial flips it around: you publish a signed advert listing
your own endpoint(s), so any other operator who knows your
npub can dial you the same way you dialed `test-us01`.

The whole exercise should take about ten minutes if you have
a public IP or a UDP listener that's reachable from outside.
A short final section covers `udp:nat` best-effort hole-punching
for the cases where direct UDP advertising isn't an option.

## What you'll build

```text
   ┌───────────────────────┐
   │   your fips daemon    │
   │   persistent npub     │
   └──────────┬────────────┘
              │ signed advert (Kind 37195)
              │   { udp:<your-public-ip>:2121, ... }
              │ refreshes every 30 min
              ▼
   ┌──────────────────────────────────────────┐
   │ Nostr relays                             │
   │   relay.damus.io / nos.lol / offchain.pub│
   └──────────────────────┬───────────────────┘
                          │
                          │ "what's <your-npub>'s endpoint?"
                          │
              ┌───────────┴───────────┐
              │  another fips daemon  │
              │  knows your npub,     │
              │  via_nostr: true      │
              └───────────────────────┘
```

You will change two things in `/etc/fips/fips.yaml`:

- Flip `discovery.nostr.advertise` from `false` to `true`.
- Add `advertise_on_nostr: true` and `public: true` under
  `transports.udp`.

After restart, your daemon publishes a Kind 37195 event tied
to your npub, listing the UDP endpoint other peers should
dial.

## How advertising works

> **Adverts are signed Nostr events.** Every advert is a Kind
> 37195 event signed by your daemon's secret key. Anyone
> reading it can verify the advert really came from the npub
> claiming the endpoint. The advert is the `(npub → current
> endpoints)` mapping, signed and published.

The advert lists transports the daemon is willing to expose,
and only those:

> **Endpoints are opt-in per transport.** Only transports
> with `advertise_on_nostr: true` are listed in your advert.
> Transports without that flag stay private — they still
> work for peers who reach you via static config, but they
> won't appear in your published advert.

For UDP specifically, the daemon needs to know what IP and
port to put in the advert:

> **Determining the advertised endpoint (wildcard-bound UDP).**
> With UDP bound to a wildcard like `0.0.0.0:2121`, the daemon
> doesn't know its own public IP at startup. You have two ways
> to tell it what to put in the advert:
>
> - `public: true` — daemon does a one-shot STUN observation
>   against the configured STUN servers and uses the reflexive
>   IPv4 it learns. Right when your public IP is dynamic or
>   you'd rather not pin it in config. Note: STUN observes the
>   reflexive IP from an ephemeral socket, then pairs it with
>   the listener's bind port for the advert — the advert is
>   only useful if your listener really is reachable at that
>   public IP/port, which the daemon can't tell from STUN
>   alone. A manual probe from a second host is the only sure
>   check.
> - `external_addr: "<ip>[:<port>]"` — explicit override.
>   Right when you already know your public IP — a static
>   residential IP, an Elastic IP behind 1:1 NAT, a cloud
>   instance whose advertised port differs from the bind
>   port — and you don't want to depend on STUN reachability.
>   Required for TCP on cloud setups where binding directly
>   to the public IP returns `EADDRNOTAVAIL`.
>
> If you bind UDP to a specific public IP rather than
> `0.0.0.0`, neither STUN nor `external_addr` is needed — but
> `advertise_on_nostr: true` and `public: true` are still both
> required for the daemon to publish the endpoint.

Adverts don't sit on the relays forever:

> **TTL and refresh.** Adverts have a 1-hour expiration
> (NIP-40 `expiration` tag) and the daemon re-publishes every
> 30 minutes. If your daemon goes offline, your advert decays
> from caches in roughly an hour and consumers stop trying.

## Step 1: Confirm your starting state

You should be coming out of
[resolve-peers-via-nostr](resolve-peers-via-nostr.md) with:

- A persistent npub (`fipsctl show status | grep '"npub"'`).
- Nostr discovery in consume-only mode
  (`discovery.nostr.enabled: true`,
  `discovery.nostr.advertise: false`).
- A peer entry for `test-us01` with `via_nostr: true` and no
  static address. `fipsctl show peers` shows the link
  established.

If any of those isn't true, finish the previous tutorials
first.

Capture your npub now — you'll need it for the verification
step:

```sh
sudo fipsctl show status | grep '"npub"'
```

Copy the value.

## Step 2: Enable advertising in the config

Open `/etc/fips/fips.yaml` and change two things.

**Change 1: flip `advertise` to `true`.** Find the
`discovery.nostr` block under `node:` and set:

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

(The previous tutorial set `advertise: false`; you're flipping
that bit now.)

**Change 2: add the UDP advert flags.** Find the `udp:` block
under `transports:`. The wildcard-bind default
(`0.0.0.0:2121`) means the daemon needs help knowing what to
advertise — pick one of the two approaches from the callout
above.

If you want STUN auto-discovery (works for full-cone NATs and
nodes with a directly-bound public IP):

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

If you already know your public IP (e.g., a static residential
IP or a cloud Elastic IP behind 1:1 NAT) and want to skip the
STUN dependency:

```yaml
transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    advertise_on_nostr: true
    public: true
    external_addr: "203.0.113.45:2121"
```

Replace `203.0.113.45:2121` with your actual public IP and
port. The bare-IP form `external_addr: "203.0.113.45"` is also
accepted; the daemon combines it with the bind port. `public:
true` is still required as the master switch that gates UDP
advertisement; setting `external_addr` alongside it wins, and
STUN auto-discovery is skipped entirely (no logging
cross-check).

`advertise_on_nostr: true` is the bit that says "include this
transport in my published advert" — common to both paths.

Save the file.

## Step 3: Restart the daemon

```sh
sudo systemctl restart fips
sudo systemctl status fips
```

Status should show `active (running)`. Within a few seconds the
daemon will:

1. Determine the address to advertise. If you set `external_addr`,
   the daemon uses it directly and skips STUN. If you set only
   `public: true`, the daemon runs a one-shot STUN observation
   against the default STUN servers and uses the reflexive IPv4 it
   learns.
2. Build a Kind 37195 advert listing
   `udp:<public-ip>:2121` (and any other transports you have
   `advertise_on_nostr: true` on).
3. Sign the advert with the daemon's nsec.
4. Publish it to the three default advert relays.
5. Schedule a refresh every 30 minutes.

If you took the `public: true` path and STUN fails (for example,
the network blocks outbound UDP/3478), the daemon emits a WARN
line in the journal and suppresses the UDP entry from the advert
rather than publishing a wrong address. The link to `test-us01`
from the previous tutorial keeps working regardless — only the
publish side is gated on STUN, and only on the STUN path. The
`external_addr` path doesn't depend on STUN reachability at all.

Quick sanity check on the journal:

```sh
sudo journalctl -u fips -n 200 | grep -iE 'STUN|advert|warn' | head -20
```

If you see `WARN` lines mentioning STUN or wildcard-bind
fallthrough, jump to [Troubleshooting](#troubleshooting); the
rest of the tutorial assumes the publish succeeded.

## Step 4: Verify your advert is on the network

The advert is a public Nostr event — anyone, including you,
can fetch it. With the `nak` Nostr CLI installed, query the
relays for adverts published by your npub:

```sh
nak req -k 37195 -d "fips-overlay-v1" \
    -a $(nak decode <your-npub> | jq -r .pubkey) \
    --limit 1 wss://relay.damus.io
```

Replace `<your-npub>` with the npub you copied in Step 1. The
inner `nak decode` converts your bech32 npub to the hex pubkey
the relay filter expects.

Expect one event back. The interesting fields:

- `pubkey` — your npub in hex form.
- `tags` — includes `["d","fips-overlay-v1"]` (the namespace),
  `["protocol","fips-overlay-v1"]`, and an `["expiration", …]`
  tag set ~1 hour in the future.
- `content` — JSON listing the `endpoints` array. You should
  see one entry like:

  ```json
  {"transport":"udp","addr":"<your-public-ip>:2121"}
  ```

That `<your-public-ip>` is what STUN learned. Confirm it
matches what you'd expect for your network — for a home node,
it should be your residential IP, not a `192.168.x.x` LAN
address.

## Step 5: Watch for inbound connections

Your advert is now consumable by any FIPS daemon running open
discovery on the same `fips-overlay-v1` namespace. The public
test mesh nodes do exactly this — they subscribe to all
adverts in the namespace and try to dial new publishers.

Within a minute or two of restart, run:

```sh
sudo fipsctl show peers
```

In addition to your configured `test-us01` peer, you may see
an entry for `test-us03` (the open-discovery test mesh node).
It will have `connectivity` active and its own
`transport_addr`. This peering appeared without you
configuring anything — the test-mesh open-discovery node saw
your advert, dialed the endpoint, and Noise IK established
the link.

If no inbound peers appear, that's not necessarily a failure
of advertising — it just means no one has consumed your advert
*and* dialed back yet. The advert is on the relays regardless,
verifiable in Step 4.

## What you've learned

- **Adverts are publish + sign.** Every running FIPS daemon
  with `advertise: true` publishes a signed advert; reading it
  is one Nostr event lookup.
- **Endpoint inclusion is per-transport.** Only the transports
  you set `advertise_on_nostr: true` on appear in the advert.
- **`public: true` invokes STUN.** Wildcard-bound UDP with
  `public: true` runs a one-shot STUN observation to learn
  its public IP.
- **Refresh is automatic.** Adverts re-publish every 30
  minutes; consumers cache them with a 1-hour staleness
  bound.
- **The publish side stands alone.** Once your advert is on
  the relays, peers can dial you whether you're advertising
  to them specifically or not. The test mesh's open-discovery
  nodes will pick you up automatically.

## If your direct UDP advert isn't reachable

`public: true` advertises the IP STUN observes paired with your
listener's bind port. That advert is only useful if your listener
really is reachable at that public IP/port — STUN can confirm the
public IP but not that an unsolicited inbound packet to the bind
port will make it through. The most common cause of the listener
being unreachable is symmetric NAT (where the public port a peer
sees varies per remote endpoint), but other configurations can
have the same effect.

When direct UDP advertising can't be relied on, the alternative
is `udp:nat` mode, which advertises a placeholder `udp:nat`
endpoint along with the daemon's signaling-relay and STUN-server
lists, and performs UDP hole-punching at dial time. Hole-punching
is best-effort — it works reliably when both sides are full-cone
or port-restricted, and symmetric NAT on either side typically
defeats it. Both sides need matching configs.

The minimal config switch:

```yaml
transports:
  udp:
    bind_addr: "0.0.0.0:2121"
    advertise_on_nostr: true
    public: false                 # ← was true; change to false
```

And add the signaling/STUN block under `discovery.nostr`:

```yaml
discovery:
  nostr:
    enabled: true
    advertise: true
    dm_relays:
      - "wss://relay.damus.io"
      - "wss://nos.lol"
    stun_servers:
      - "stun:stun.l.google.com:19302"
      - "stun:stun.cloudflare.com:3478"
```

For the full setup including peer-side config and the punch-
duration knob, see
[../how-to/enable-nostr-discovery.md § When the node is behind NAT](../how-to/enable-nostr-discovery.md#when-the-node-is-behind-nat).

Separately from NAT considerations, FIPS supports running a
node behind a Tor onion service as a deployment shape in its
own right — chosen for the privacy, anonymity, and
censorship-resistance properties it brings, not as a fallback
when UDP or TCP fail. If those properties are an independent
goal for your node, see
[../how-to/enable-nostr-discovery.md § Tor onion node](../how-to/enable-nostr-discovery.md#tor-onion-node)
and
[../how-to/deploy-tor-onion.md](../how-to/deploy-tor-onion.md).

## Troubleshooting

If your advert doesn't appear on the relays:

- **STUN failed.** Check the journal for WARN lines mentioning
  STUN or wildcard-bind. The most common causes are outbound
  UDP/3478 blocked or DNS for `stun.l.google.com` failing.
  Try: `dig stun.l.google.com` and
  `nc -uvz stun.l.google.com 19302` to verify reachability.
- **Wrong public IP advertised.** If `nak` shows your advert
  with a non-public address (e.g., `10.x.x.x` or
  `192.168.x.x`), STUN didn't see your real public IP — likely
  you're behind a CGNAT that NATs your STUN traffic too, or a
  corporate firewall that proxies it. Two correct fixes:
  (a) keep `public: true` and add `external_addr: <your-IP>`
  (the explicit override wins and skips STUN); or (b) bind
  directly to your public interface
  (`bind_addr: <pub-ip>:2121`) and keep `advertise_on_nostr:
  true` and `public: true`. Don't drop those flags.

- **Relay reachability.** `nak req` against a relay you can
  reach but no events return — possibly the publish failed
  silently because the daemon couldn't connect to that
  specific relay. Try the other two:

  ```sh
  nak req ... wss://nos.lol
  nak req ... wss://offchain.pub
  ```

- **`advertise_on_nostr` typo.** YAML is case-sensitive. The
  config parser rejects unknown keys via
  `serde(deny_unknown_fields)` on the per-section structs, so a
  misspelled field will refuse the daemon's start with a
  parse-error line in the journal naming the unknown field.
  If the daemon is running but `nak` returns no advert, the
  field was accepted but something else is wrong; double-check
  the spelling on the UDP block and that
  `discovery.nostr.advertise: true` is also set.

## What's next

- **Open discovery.**
  [open-discovery](open-discovery.md) flips the consume side
  symmetric — switch your daemon to `policy: open` and watch
  your peer list populate from the ambient
  `fips-overlay-v1` namespace, the same mechanism
  `test-us03` is using right now to find you.

- **Host a service of your own.**
  [host-a-service](host-a-service.md) walks through bringing up
  an HTTP server addressable as `<your-npub>.fips`, the same
  way the connecting node now reaches `test-us01`. The natural
  follow-on now that other operators can dial you by npub.

For the operator-style scenario reference covering all five
shapes of Nostr discovery side-by-side (consume-only,
publish-direct, publish-Tor, NAT traversal, open):

- [../how-to/enable-nostr-discovery.md](../how-to/enable-nostr-discovery.md)

For the wire-format and discovery design:

- [../reference/nostr-events.md](../reference/nostr-events.md)
  — Kind 37195 advert format, Kind 21059 traversal signaling.
- [../design/fips-nostr-discovery.md](../design/fips-nostr-discovery.md)
  — discovery runtime design, security and threat model.
