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cmd/containerboot: clamp MSS to PMTU for proxy group pods (#19686)

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Single-pod ingress/egress proxies already called ClampMSSToPMTU when
setting up forwarding rules, but the proxy group (HA) code paths in
egressservices.go and ingressservices.go did not. This caused TCP
connections through proxy group pods to suffer from MSS/MTU mismatch
issues in environments where path MTU discovery is not working.

Add ClampMSSToPMTU calls in the egress sync loop (alongside the existing
EnsureSNATForDst call) and in addDNATRuleForSvc (alongside the existing
EnsureDNATRuleForSvc call), mirroring what the single-pod forwarding
rules already do.

Also add MSS clamping assertions to TestSyncIngressConfigs and track
ClampMSSToPMTU calls in FakeNetfilterRunner.

Fixes issue #19812 https://github.com/tailscale/tailscale/issues/19812.
Tracking internal ticket TSS-86326.

Signed-off-by: Jay Tung <ltung@crusoeenergy.com>
Co-authored-by: Jay Tung <ltung@crusoeenergy.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
dragondscv
2026-05-28 12:57:38 +01:00
committed by GitHub
co-authored by Jay Tung Claude
parent 782c73bf41
commit 4b8115bb2c
4 changed files with 60 additions and 5 deletions
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util/linuxfw/fake_netfilter.go
+11 -1
View File
@@ -19,6 +19,8 @@ type FakeNetfilterRunner struct {
TailscaleServiceIP netip.Addr
ClusterIP netip.Addr
}
// clampedAddrs tracks addresses passed to ClampMSSToPMTU.
clampedAddrs []netip.Addr
}
// NewFakeNetfilterRunner creates a new FakeNetfilterRunner.
@@ -83,7 +85,15 @@ func (f *FakeNetfilterRunner) DNATWithLoadBalancer(origDst netip.Addr, dsts []ne
}
func (f *FakeNetfilterRunner) EnsureSNATForDst(src, dst netip.Addr) error { return nil }
func (f *FakeNetfilterRunner) DNATNonTailscaleTraffic(tun string, dst netip.Addr) error { return nil }
func (f *FakeNetfilterRunner) ClampMSSToPMTU(tun string, addr netip.Addr) error { return nil }
func (f *FakeNetfilterRunner) ClampMSSToPMTU(tun string, addr netip.Addr) error {
f.clampedAddrs = append(f.clampedAddrs, addr)
return nil
}
// GetClampedAddrs returns the addresses passed to ClampMSSToPMTU.
func (f *FakeNetfilterRunner) GetClampedAddrs() []netip.Addr {
return f.clampedAddrs
}
func (f *FakeNetfilterRunner) AddMagicsockPortRule(port uint16, network string) error { return nil }
func (f *FakeNetfilterRunner) DelMagicsockPortRule(port uint16, network string) error { return nil }
func (f *FakeNetfilterRunner) DeletePortMapRuleForSvc(svc, tun string, targetIP netip.Addr, pm PortMap) error {