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fips/docs/tutorials/reach-mesh-services.md
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connectivity states in three tutorials were invented, and their jq filters
matched nothing including healthy peers. One command filtered on a literal
fd97: address prefix, which only the first byte of fixes, so it returned
empty for all but one reader in 256 and every later step using the
variable failed silently. transports.tor.advertise_on_nostr was
undocumented despite being validated against node.rendezvous.nostr.enabled.

The transport design document gains the BLE section it never had, written
from the source: the backend cascade and its compile_error tripwire, the
platform gate, the PSM advertisement wire layout and the byte budget that
forces a 16-bit service-data key, and the probe and admission bounds.

Three source files carried the same class of staleness and are corrected
with the documentation: the OpenWrt ipk usage line and Makefile error text
both named a packaging/openwrt that does not exist, and chaos.sh parsed
--subnet without listing it.

Folded in with the content commit, having been prepared alongside it:

The three GitHub Action pins that had gone stale. Every third-party
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and re-resolving all ten against their tags found dorny/test-reporter@v2,
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three install-action@nextest references stay unpinned, since that action
reads the tool to install from the ref name. check-action-pins.sh passes
at 75 references and all nine workflow files parse.

The lockfile refresh, which is the mutating half of the dependency sweep.
Thirty-six packages move to their latest semver-compatible versions and
every one is transitive; nothing declared in Cargo.toml changes version.
No advisory forces any of them. It was taken before the validation
battery, because a gate run against a lockfile that later moves proves
nothing about what ships.

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three of the four deferred at v0.4.0 for change surface rather than
security. All three land with no source change. sha2 and hkdf must move
together, since both depend on digest 0.11, and neither changes an
algorithm. That matters because the chaining-key KDF in the Noise
handshake is built on Hkdf::<Sha256>, where an output change would be a
wire break rather than a compile error; no known-answer vectors exist for
that path, so the wire-compatibility gate is what covers it. secp256k1
0.31 is deliberately absent, since nostr's own requirement would leave
two copies of the ECC library in the tree.

The README support matrix, rebuilt as one feature table broken out by
Linux variety. A single Linux column hid that Debian, Ubuntu, Arch and
NixOS are one glibc build differing in packaging, that OpenWrt is musl
and drops BLE, and that Android is not a daemon platform. Transport rows
sort by how many platforms carry them. A Native API row reads its
platform set from the cfg gates. The installer row becomes a package
format row naming the artifact, and only the .deb is exercised per
release.

Four changelog and release-note gaps the BLE re-walk found: a Bluetooth
LE bullet stranded inside the released 0.4.2 section, a missing Fixed
entry for the scan and probe loop counting a pool-refused connection as
an established link, the unnamed embedder call that installs an
application-owned radio, and the fact that stopping the transport now
stops scanning as well as advertising.

Three release-document gaps found walking the unsurveyed commits: the UDP
reuse-flag fix stated in the direction opposite to the one it was made,
with the silent second-daemon bind it prevents left unsaid; the corrected
native-API socket paragraph carried into both release-note copies, which
still named SOCK_SEQPACKET on FreeBSD and two kernels where three are
handled; and the coordinate-cache hardening, which shipped with no text
anywhere despite adding four operator-visible status fields. That last
entry states plainly that the checks are mitigations and not a closure,
since the coordinate is still not authenticated.

Also folded in, the documentation pass that followed the content commit:

A stage-pipeline diagram for the probe, embedded in the fipsctl
reference under the five-stage list. It draws the five stages left to
right with each stage's failure reasons below it, and the bypass that
skips both lookup stages when the coordinates are cached or the target
is a direct peer. Its branches come from the probe state machine rather
than from the report, so the path stage is drawn as the one failure that
does not stop the probe.

A rewrite of the README's "What FIPS does" section. It now opens with
what a machine running FIPS gets, rather than with the two deployment
modes, and gives the self-organizing and permissionless property its own
paragraph since it holds for both modes.

A regrouping of the README's feature list into the mesh, getting traffic
onto it, and running a node, with a bullet added for the native datagram
API, which had none despite sitting in the support matrix. The Quick
start now leads with the released packages rather than a source build.
It also fixes a real defect: the package enables fips.service and
fips-dns.service and starts neither on a fresh install, so .fips name
resolution was silently dead until the next reboot and neither page said
to start the service.

A rewrite of the release notes. They opened with seven subsections of
upgrade caveats and reached the first feature two hundred lines in; they
now open with a summary of the release and elaborate below it in the
same order. Android is stated as supported through an embedded crate
rather than as a standalone daemon, consistently across all three
documents. The OpenWrt pair is corrected: it is 802.11s between routers
with FIPS supplying encryption, authentication and routing, plus a
convention of an open !FIPS SSID a client joins over WiFi, not meshing
over a router's own radios. The probe's path output is described as the
least-common-ancestor walk, which is the worst-case fallback route
rather than the route a packet takes. Detail that did not change what a
reader does was cut from the notes and kept in the changelog.
2026-08-30 10:42:59 +00:00

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Markdown

# Reach Services on Other Mesh Nodes
In [join-the-test-mesh](join-the-test-mesh.md) you used `ping6`
to reach `test-us01` and `test-us02` by their `.fips` names.
This tutorial generalizes that to any IPv6-capable tool you
already use — `nc`, `traceroute6`, `curl`, `ssh`, `scp`,
anything — and gets you comfortable with the daemon's IPv6
adapter, which makes the FIPS mesh look like an ordinary IPv6
network to applications that already know how to use IPv6.
The whole exercise should take about ten minutes.
## What you'll do
You'll ping a mesh node (recap), attempt a TCP connection to it
with `nc`, and trace the packet path with `traceroute6` — all
by hostname. By the end you will have driven three different
IPv6 tools at a mesh address and seen each one work the same
way it works on the regular internet.
> **An IPv6 adapter for a non-IPv6 mesh.** The FIPS network
> itself routes blobs of data between npub-addressed nodes;
> on its own it has nothing to do with IPv6. The daemon
> includes an *IPv6 adapter* that presents the mesh as an
> ordinary IPv6 interface (`fips0`), so existing IP software
> works without modification. The kernel routes packets to
> it, applications open IPv6 sockets through it, and the
> adapter handles encapsulating each packet and routing it
> through the mesh to the matching adapter on the other side.
> Any tool that speaks IPv6 works unchanged.
The IPv6 adapter is currently the main way operators use the
FIPS network, which is why most of the new-user progression is
about it. Native applications can use the mesh without going
through IPv6 at all, but that is out of scope for this tutorial.
## Addressing a mesh node
Throughout this tutorial — and any time you reach across the
mesh — use a node's `.fips` hostname directly. There are two
forms:
- **`<npub>.fips`** — the canonical form. Every node has one,
always. This is the long bech32 npub with `.fips` appended.
- **`<shortname>.fips`** — the convenience form, *if* you (or
the package) have an entry for the node in
`/etc/fips/hosts`. The installer ships entries for the
public test mesh, so `test-us01.fips` works on a fresh
install.
These are real hostnames as far as your kernel is concerned.
Pass them to any IPv6-capable tool — `ping6`, `nc`, `curl`,
`ssh`, `traceroute6`, anything — the same way you would pass a
hostname on the public internet. There is no separate
"resolve to address first" step you ever need to perform; if
the tool takes a hostname, it accepts a `.fips` hostname.
> **Where the address comes from.** Every FIPS node's mesh
> address is `0xfd` (the `fd00::/8` ULA prefix) followed by the
> first 15 bytes of its node address, which is itself the first
> 16 bytes of SHA-256 of its public key. The remaining bytes
> are hash output, so an address like `fd97:...` is per-node —
> the `97` is part of the hash, not a fixed prefix shared across
> nodes. Names of the form `<npub>.fips` and any shortname
> mapped in `/etc/fips/hosts` are aliases for that address. The
> daemon's local DNS responder hands the answer back to your
> kernel without ever talking to a remote DNS server.
## Step 1: Ping a mesh node (recap)
```sh
ping6 -c 4 test-us01.fips
```
You did this in [join-the-test-mesh](join-the-test-mesh.md).
Four replies, RTT in the tens of milliseconds (depending on
where you are relative to `test-us01`). Nothing new — but it
confirms the mesh data plane is healthy before you try
anything else.
## Step 2: Attempt a TCP connection
`ping6` proves ICMPv6 reaches the destination. To prove TCP
reaches it, use `nc` (netcat) to attempt a connection to a port.
Pick any port — whether it has a service listening or not, the
attempt proves the data plane carries your TCP segments
end-to-end:
```sh
nc -6 -vz test-us01.fips 22 2>&1
```
You will see one of two outcomes:
```text
Connection to test-us01.fips 22 port [tcp/ssh] succeeded!
```
or:
```text
nc: connect to test-us01.fips port 22 (tcp) failed: Connection refused
```
Both are good. The first means a service is listening on that
port and accepted your TCP handshake. The second means your TCP
SYN reached the remote node's kernel, which sent back a TCP RST
because no service was bound — and that RST traveled all the way
back through the mesh to your `nc` process.
> **What a `Connection refused` proves.** A connection-refused
> response is *not* a network failure. It means the destination
> host is alive and reachable, the TCP stack on the far end
> processed your SYN, and the reply made it home. Compare with
> what you would get if the address were unreachable:
> `Network is unreachable` or a timeout. Either of the two
> outcomes above demonstrates a working end-to-end TCP path.
If the port you tried happens to have a service, attach `-`
instead of `-z` and you can read the banner directly:
```sh
nc -6 -v test-us01.fips 22
```
The remote node's SSH banner, if any, will print on the next
line. Type `Ctrl-C` to disconnect — you have not authenticated,
just banner-grabbed.
If `nc` is not installed, the same demonstration works with
`curl` against TCP/80:
```sh
curl -6 -v --connect-timeout 5 http://test-us01.fips/ 2>&1 | head
```
The TCP connection result is in the first few lines of `curl`'s
verbose output. The HTTP response code is irrelevant — what
matters is whether the connection itself succeeded.
## Step 3: Trace the path
`traceroute6` shows the IPv6 hops between you and a
destination:
```sh
traceroute6 -n test-us02.fips
```
You will see exactly one line — `test-us02`'s mesh address.
That is the only IPv6 hop between your `fips0` and
`test-us02`'s `fips0`, even though at the FIPS-mesh layer
your packet is being forwarded through your peer `test-us01`
on the way to `test-us02`. The mesh-layer forwarding is
invisible to `traceroute6` because it lives below the IPv6
adapter.
> **Two layers, two ideas of "hop".** The FIPS mesh routes
> blobs between npub-addressed nodes and can pass through
> several intermediate peers — your packet to `test-us02` is
> handed off to `test-us01` first. The IPv6 adapter, sitting
> on top of that, presents every reachable mesh node as a
> direct IPv6 neighbor: one hop, on a flat fabric. From
> `traceroute6`'s perspective the multi-hop FIPS path is
> hidden — it sees only the source and destination IPv6
> adapters. To see what's happening at the mesh layer, see
> [ipv6-adapter-walkthrough](ipv6-adapter-walkthrough.md),
> which traces one `ssh` request from DNS query to far-side
> TUN with `fipstop` and `fipsctl` running alongside.
If `traceroute6` is not installed, `mtr` and other IPv6 path
tools produce the same single-hop result. The single-hop
behavior is a property of the IPv6 adapter, not of the tool.
## What you've learned
You have driven three IPv6 tools at mesh nodes you reach over
the mesh, all by `.fips` hostname, and they all worked the same
way they work everywhere else:
- **Addressing.** `<npub>.fips` is the canonical hostname for
any node; `<shortname>.fips` is the convenience form when
`/etc/fips/hosts` has an entry. Use these in any tool that
takes an IPv6 hostname — there is no separate resolution
step you ever need to perform.
- **Reachability.** `ping6` confirms the remote node's `fips0`
answers ICMPv6 echo from your `fips0`.
- **TCP.** `nc` confirms TCP segments traverse the mesh and the
far side responds (whether with a banner, a refusal, or a
service of its own).
- **Path.** `traceroute6` shows exactly one IPv6 hop to any
reachable mesh node, because the multi-hop FIPS-mesh-layer
forwarding lives below the IPv6 adapter and is invisible
to IPv6 tooling.
The conceptual takeaway is the one in the callout at the top:
the daemon's IPv6 adapter takes care of presenting the FIPS
mesh as ordinary IPv6 to every tool you already know. To
consume any service hosted on any mesh node — SSH, HTTP, file
transfer, custom protocols — you use the IPv6 client you
would use anywhere else. The hostname looks unusual
(`<npub>.fips`), but the API surface is unchanged.
## Troubleshooting
If a tool reports "Network is unreachable" or hangs:
- **Confirm the link is healthy.**
`sudo fipsctl show peers` should show `test-us01` with active
connectivity. If the link to your direct peer is down, nothing
past it is reachable.
- **Confirm `fips0` is up.** `ip -6 addr show fips0` should show
one `fd97:...` address. If `fips0` is missing, the daemon did
not bring up the TUN — verify the daemon is running with the
privileges it needs. The default is to run as root; if you
dropped privileges per
[../how-to/run-as-unprivileged-user.md](../how-to/run-as-unprivileged-user.md),
re-check that the `setcap` and systemd override survived your
last package upgrade.
- **Confirm the name resolves.** If `ping6 test-us01.fips`
fails with `unknown host` or `Name or service not known`,
the system resolver is not consulting the daemon's `.fips`
responder. The installer wires this up automatically; the
"Reaching mesh nodes by name" section of
[../getting-started.md](../getting-started.md) describes
what the wiring looks like and how to confirm it.
If `nc` or `curl` reports a timeout (rather than a refusal or
success), the destination node is unreachable from your
daemon — possible mesh-routing transient. Try again, or ping
first: if `ping6` succeeds but TCP times out, it is the
specific port being filtered on the destination, not a path
problem.
## What's next
- [host-a-service](host-a-service.md) — Bring up a small HTTP
server on your node, bind it to `fips0` so it is mesh-only,
and confirm another mesh node (or your own machine) can
reach it through the same data plane you just exercised.
Covers bind-interface choice and the mesh firewall.
For "what's actually in those packets":
- [../design/fips-architecture.md](../design/fips-architecture.md)
— the protocol stack and the two-layer encryption model.
- [../design/fips-mesh-layer.md](../design/fips-mesh-layer.md) —
Noise IK link encryption, hop-by-hop forwarding.
- [../design/fips-session-layer.md](../design/fips-session-layer.md)
— end-to-end Noise XK between source and destination.
For the trace-it-yourself version of the path you just
exercised, see
[ipv6-adapter-walkthrough](ipv6-adapter-walkthrough.md), which
walks one `ssh` from DNS query through session setup to the
far-side TUN with `fipstop` and `fipsctl` running alongside.