fix: stop selecting direct connections with too-small MTU #85
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| @@ -77,8 +77,8 @@ func TestMarshalAndParse(t *testing.T) { | |||
| } | |||
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| gotHex := fmt.Sprintf("% x", got) | |||
| if gotHex != tt.want { | |||
| t.Fatalf("wrong marshal\n got: %s\nwant: %s\n", gotHex, tt.want) | |||
| if !strings.HasPrefix(gotHex, tt.want) { | |||
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If we expect the end of the ping payload to be a bunch of 00s we should probably test that, either by changing the want for each of the ping/pong cases to be the full value or by some other method
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We don't care that it's zeros per se, but I'll add a check that it's the padded length.
deansheather
approved these changes
Jun 10, 2025
ethanndickson
approved these changes
Jun 10, 2025
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spikecurtis
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Jun 11, 2025
Fixes #15523 Uses latest https://github.com/coder/tailscale which includes coder/tailscale#85 to stop selecting paths with small MTU for direct connections. Also updates the tailnet integration test to reproduce the issue. The previous version had the 2 peers connected by a single veth, but this allows the OS to fragment the packet. In the new version, the 2 peers (and server) are all connected by a central router. The link between peer 1 and the router has an adjustable MTU. IPv6 does not allow packets to be fragmented by intermediate routers, so sending a too-large packet in this scenario forces the router to drop packets and reproduce the issue (without the tailscale changes).
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related to: coder/coder#15523
This PR:
The end result is that Disco Ping and Pong packets are not directly exchanged over paths with too-small MTU, and thus, those endpoints are not chosen for direct connections. (Alternate direct paths with bigger MTU may be chosen, or we may fall back to DERP.)