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cmd/containerboot: clamp MSS to PMTU for proxy group pods (#19686) (#19900)

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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.




(cherry picked from commit 4b8115bb2c)

Signed-off-by: Jay Tung <ltung@crusoeenergy.com>
Co-authored-by: dragondscv <dragondscv@gmail.com>
Co-authored-by: Jay Tung <ltung@crusoeenergy.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
David Bond
2026-05-28 13:22:46 +01:00
committed by GitHub
parent 49d7ad38b3
commit 5f390d4845
4 changed files with 60 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
cmd/containerboot/egressservices.go
View File

@@ -250,6 +250,9 @@ func (ep *egressProxy) syncEgressConfigs(cfgs egressservices.Configs, status *eg
if err := ep.nfr.EnsureSNATForDst(local, t); err != nil {
return nil, fmt.Errorf("error setting up SNAT rule: %w", err)
}
if err := ep.nfr.ClampMSSToPMTU(tailscaleTunInterface, t); err != nil {
return nil, fmt.Errorf("error clamping MSS to PMTU: %w", err)
}
}
}
// Update the status. Status will be written back to the state Secret by the caller.

8
cmd/containerboot/ingressservices.go
View File

@@ -265,7 +265,13 @@ func ensureIngressRulesAdded(cfgs map[string]ingressservices.Config, nfr linuxfw
func addDNATRuleForSvc(nfr linuxfw.NetfilterRunner, serviceName string, tsIP, clusterIP netip.Addr) error {
log.Printf("adding DNAT rule for Tailscale Service %s with IP %s to Kubernetes Service IP %s", serviceName, tsIP, clusterIP)
return nfr.EnsureDNATRuleForSvc(serviceName, tsIP, clusterIP)
if err := nfr.EnsureDNATRuleForSvc(serviceName, tsIP, clusterIP); err != nil {
return err
}
if err := nfr.ClampMSSToPMTU(tailscaleTunInterface, clusterIP); err != nil {
return fmt.Errorf("error clamping MSS to PMTU: %w", err)
}
return nil
}
// ensureIngressRulesDeleted takes a map of Tailscale Services and rules and ensures that the firewall rules are deleted.

42
cmd/containerboot/ingressservices_test.go
View File

@@ -7,6 +7,7 @@
import (
"net/netip"
"slices"
"testing"
"tailscale.com/kube/ingressservices"
@@ -22,6 +23,7 @@ func TestSyncIngressConfigs(t *testing.T) {
TailscaleServiceIP netip.Addr
ClusterIP netip.Addr
}
wantClampedAddrs []netip.Addr // cluster IPs that should have MSS clamping applied
}{
{
name: "add_new_rules_when_no_existing_config",
@@ -35,6 +37,7 @@ func TestSyncIngressConfigs(t *testing.T) {
}{
"svc:foo": makeWantService("100.64.0.1", "10.0.0.1"),
},
wantClampedAddrs: []netip.Addr{netip.MustParseAddr("10.0.0.1")},
},
{
name: "add_multiple_services",
@@ -52,6 +55,11 @@ func TestSyncIngressConfigs(t *testing.T) {
"svc:bar": makeWantService("100.64.0.2", "10.0.0.2"),
"svc:baz": makeWantService("100.64.0.3", "10.0.0.3"),
},
wantClampedAddrs: []netip.Addr{
netip.MustParseAddr("10.0.0.1"),
netip.MustParseAddr("10.0.0.2"),
netip.MustParseAddr("10.0.0.3"),
},
},
{
name: "add_both_ipv4_and_ipv6_rules",
@@ -65,6 +73,10 @@ func TestSyncIngressConfigs(t *testing.T) {
}{
"svc:foo": makeWantService("2001:db8::1", "2001:db8::2"),
},
wantClampedAddrs: []netip.Addr{
netip.MustParseAddr("10.0.0.1"),
netip.MustParseAddr("2001:db8::2"),
},
},
{
name: "add_ipv6_only_rules",
@@ -78,6 +90,7 @@ func TestSyncIngressConfigs(t *testing.T) {
}{
"svc:ipv6": makeWantService("2001:db8::10", "2001:db8::20"),
},
wantClampedAddrs: []netip.Addr{netip.MustParseAddr("2001:db8::20")},
},
{
name: "delete_all_rules_when_config_removed",
@@ -94,6 +107,7 @@ func TestSyncIngressConfigs(t *testing.T) {
TailscaleServiceIP netip.Addr
ClusterIP netip.Addr
}{},
wantClampedAddrs: nil, // no rules added, no clamping
},
{
name: "add_remove_modify",
@@ -117,6 +131,10 @@ func TestSyncIngressConfigs(t *testing.T) {
"svc:foo": makeWantService("100.64.0.1", "10.0.0.2"),
"svc:new": makeWantService("100.64.0.4", "10.0.0.4"),
},
wantClampedAddrs: []netip.Addr{
netip.MustParseAddr("10.0.0.2"),
netip.MustParseAddr("10.0.0.4"),
},
},
{
name: "update_with_outdated_status",
@@ -152,12 +170,17 @@ func TestSyncIngressConfigs(t *testing.T) {
"svc:web-ipv6": makeWantService("2001:db8::10", "2001:db8::20"),
"svc:api": makeWantService("100.64.0.20", "10.0.0.20"),
},
wantClampedAddrs: []netip.Addr{
netip.MustParseAddr("10.0.0.10"),
netip.MustParseAddr("10.0.0.20"),
netip.MustParseAddr("2001:db8::20"),
},
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
var nfr linuxfw.NetfilterRunner = linuxfw.NewFakeNetfilterRunner()
nfr := linuxfw.NewFakeNetfilterRunner()
ep := &ingressProxy{
nfr: nfr,
@@ -170,8 +193,7 @@ func TestSyncIngressConfigs(t *testing.T) {
t.Fatalf("syncIngressConfigs failed: %v", err)
}
fake := nfr.(*linuxfw.FakeNetfilterRunner)
gotServices := fake.GetServiceState()
gotServices := nfr.GetServiceState()
if len(gotServices) != len(tt.wantServices) {
t.Errorf("got %d services, want %d", len(gotServices), len(tt.wantServices))
}
@@ -188,6 +210,20 @@ func TestSyncIngressConfigs(t *testing.T) {
t.Errorf("service %s: got ClusterIP %v, want %v", svc, got.ClusterIP, want.ClusterIP)
}
}
gotClamped := nfr.GetClampedAddrs()
slices.SortFunc(gotClamped, func(a, b netip.Addr) int { return a.Compare(b) })
slices.SortFunc(tt.wantClampedAddrs, func(a, b netip.Addr) int { return a.Compare(b) })
if len(gotClamped) != len(tt.wantClampedAddrs) {
t.Errorf("ClampMSSToPMTU: got %v, want %v", gotClamped, tt.wantClampedAddrs)
} else {
for i := range gotClamped {
if gotClamped[i] != tt.wantClampedAddrs[i] {
t.Errorf("ClampMSSToPMTU: got %v, want %v", gotClamped, tt.wantClampedAddrs)
break
}
}
}
})
}
}

12
util/linuxfw/fake_netfilter.go
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 {