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disco,net/tstun,wgengine/magicsock: probe peer MTU

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Automatically probe the path MTU to a peer when peer MTU is enabled, but do not
use the MTU information for anything yet.

Updates #311

Signed-off-by: Val <valerie@tailscale.com>
This commit is contained in:
Val
2023-10-05 20:05:19 +02:00
committed by valscale
parent b4e587c3bd
commit 893bdd729c
7 changed files with 91 additions and 40 deletions
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13
net/tstun/mtu_test.go
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@ -39,15 +39,18 @@ func TestDefaultTunMTU(t *testing.T) {
t.Errorf("default TUN MTU = %d, want %d, clamping failed", DefaultTUNMTU(), maxTUNMTU)
}
// If PMTUD is enabled, the MTU should default to the largest probed
// MTU, but only if the user hasn't requested a specific MTU.
// If PMTUD is enabled, the MTU should default to the safe MTU, but only
// if the user hasn't requested a specific MTU.
//
// TODO: When PMTUD is generating PTB responses, this will become the
// largest MTU we probe.
os.Setenv("TS_DEBUG_MTU", "")
os.Setenv("TS_DEBUG_ENABLE_PMTUD", "true")
if DefaultTUNMTU() != WireToTUNMTU(MaxProbedWireMTU) {
t.Errorf("default TUN MTU = %d, want %d", DefaultTUNMTU(), WireToTUNMTU(MaxProbedWireMTU))
if DefaultTUNMTU() != safeTUNMTU {
t.Errorf("default TUN MTU = %d, want %d", DefaultTUNMTU(), safeTUNMTU)
}
// TS_DEBUG_MTU should take precedence over TS_DEBUG_ENABLE_PMTUD.
mtu = WireToTUNMTU(MaxProbedWireMTU - 1)
mtu = WireToTUNMTU(MaxPacketSize - 1)
os.Setenv("TS_DEBUG_MTU", strconv.Itoa(int(mtu)))
if DefaultTUNMTU() != mtu {
t.Errorf("default TUN MTU = %d, want %d", DefaultTUNMTU(), mtu)