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fix: apply MTU to multi-path routes in routetable #12948

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fix: apply MTU to multi-path routes in routetable #12948

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Copilot Jun 10, 2026
ad570e5
fix: set MTU on base kernelRoute so it applies to both single- and mu…
Copilot Jun 10, 2026
8b52f86
test: add MTU round-trip/correction test for multi-path routes
Copilot Jun 10, 2026
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2 changes: 1 addition & 1 deletion felix/routetable/route_table.go
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Original file line number Diff line number Diff line change
Expand Up @@ -778,6 +778,7 @@ func (r *RouteTable) recalculateDesiredKernelRoute(routeKey RouteKey) {
Ifindex: bestIfaceIdx,
OnLink: bestTarget.Flags()&unix.RTNH_F_ONLINK != 0,
Protocol: proto,
MTU: bestTarget.MTU,
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}
if len(bestTarget.MultiPath) > 0 {
for _, nh := range bestTarget.MultiPath {
Expand All @@ -793,7 +794,6 @@ func (r *RouteTable) recalculateDesiredKernelRoute(routeKey RouteKey) {
} else {
kernRoute.GW = bestTarget.GW
kernRoute.Ifindex = bestIfaceIdx
kernRoute.MTU = bestTarget.MTU
}
if log.IsLevelEnabled(log.DebugLevel) && !reflect.DeepEqual(oldDesiredRoute, kernRoute) {
r.logCxt.WithFields(log.Fields{
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65 changes: 65 additions & 0 deletions felix/routetable/route_table_test.go
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Expand Up @@ -1088,6 +1088,71 @@ var _ = Describe("RouteTable", func() {
Expect(dataplane.RouteKeyToRoute[mainRouteKey("10.0.0.0/24")]).To(BeZero(),
"Route should be removed when one interface deleted")
})
It("Should program MTU on a multi-path route and correct an incorrect MTU on resync", func() {
By("Creating interfaces")
addLink := dataplane.AddIface(6, "cali6", true, true)
addLink2 := dataplane.AddIface(7, "cali7", true, true)

By("Setting a multi-path route with MTU")
rt.SetRoutes(RouteClassLocalWorkload, InterfaceNone, []Target{{
Type: TargetTypeVXLAN,
RouteKey: RouteKey{
CIDR: ip.MustParseCIDROrIP("10.0.0.0/24"),
Priority: routePriorityForTest,
},
MTU: 1400,
MultiPath: []NextHop{
{
IfaceName: addLink.LinkAttrs.Name,
Gw: ip.FromString("10.0.0.6"),
},
{
IfaceName: addLink2.LinkAttrs.Name,
Gw: ip.FromString("10.0.0.7"),
},
},
}})
err := rt.Apply()
Expect(err).ToNot(HaveOccurred())

expectedRoute := netlink.Route{
Family: unix.AF_INET,
Dst: mustParseCIDR("10.0.0.0/24"),
Type: syscall.RTN_UNICAST,
Protocol: deviceRouteProtocol,
Scope: netlink.SCOPE_UNIVERSE,
Table: unix.RT_TABLE_MAIN,
Flags: syscall.RTNH_F_ONLINK,
MTU: 1400,
MultiPath: []*netlink.NexthopInfo{
{
LinkIndex: addLink.LinkAttrs.Index,
Gw: net.ParseIP("10.0.0.6").To4(),
Flags: syscall.RTNH_F_ONLINK,
},
{
LinkIndex: addLink2.LinkAttrs.Index,
Gw: net.ParseIP("10.0.0.7").To4(),
Flags: syscall.RTNH_F_ONLINK,
},
},
Priority: routePriorityForTest,
}
Expect(dataplane.RouteKeyToRoute[mainRouteKey("10.0.0.0/24")]).To(Equal(expectedRoute),
"MTU should be programmed on the multi-path route")

By("Corrupting the MTU in the dataplane behind the RouteTable's back")
corrupted := expectedRoute
corrupted.MTU = 9000
dataplane.RouteKeyToRoute[mainRouteKey("10.0.0.0/24")] = corrupted

By("Triggering a resync")
rt.QueueResync()
err = rt.Apply()
Expect(err).ToNot(HaveOccurred())
Expect(dataplane.RouteKeyToRoute[mainRouteKey("10.0.0.0/24")]).To(Equal(expectedRoute),
"resync should have corrected the incorrect MTU on the multi-path route")
})
It("Should add multiple routes with a protocol", func() {
// Route that needs to be added
addLink := dataplane.AddIface(6, "cali6", true, true)
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