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Print the allocated IPv4 address in tun-setup

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The overlay IPv4 address is not derived from the keys: it is allocated at
run time and signed, so on a fresh state directory there is nothing for
tun-setup to print. Once the agent has run, the claim is in state.sqlite,
and reading it back takes no directory lock, so tun-setup can show the
`ip address add` line while the agent is running. Records are verified on
the way out; the database is not a trust boundary.

The line needs no keep_addr_on_down and no nodad, unlike its IPv6
counterpart: Linux keeps IPv4 addresses on an interface that has lost
carrier, and IPv4 has no duplicate address detection to stall.

Also fix a race in the four-agent test. A peer counts as connected once
its session authenticates, which can precede the announcement carrying
its hostname, so reading the hostnames straight away occasionally saw
only two. It now waits for them like every other success condition.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
tsunagi
2026-09-21 14:04:44 +01:00
co-authored by Claude Opus 5
parent 8b333455f1
commit 944d98389f
4 changed files with 80 additions and 16 deletions
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README.md
+12 -2
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@@ -174,8 +174,18 @@ sudo sysctl -qw net.ipv6.conf.tsunjwc6dcrtmo5.keep_addr_on_down=1
sudo ip -6 address add fd80:1210:f724:f620:d1bb:f982:3b6e:19bd/64 dev tsunjwc6dcrtmo5 nodad
```
If you asked for IPv4 with `--ipv4-range`, `tun-setup` adds an `ip address add`
line for it too.
With IPv4 enabled, `tun-setup` adds an `ip address add` line for the overlay
IPv4 address too — but only once there is one to print. Unlike the IPv6
address, the IPv4 address is not derived from the keys: it is allocated at run
time and signed (see [docs/sync-model.md](docs/sync-model.md)), so it exists
only after the agent has run once. `tun-setup` then reads it back out of
`state.sqlite`, which does not disturb a running agent, and includes it from
then on. Until then the first `tsunagi up` prints the exact command for the
address it was given.
That IPv4 line needs no `keep_addr_on_down` and no `nodad`: Linux keeps IPv4
addresses on an interface that loses carrier, and IPv4 has no duplicate
address detection to stall. Adding it once is enough.
The MTU is 1280 because that is the minimum IPv6 requires (RFC 8200). Linux
disables IPv6 entirely on an interface below it — the per-device