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Automated cherry pick of #5997: Use 65000 MTU upper bound for interfaces in encap mode #6006

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Feb 22, 2024
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Automated cherry pick of #5997: Use 65000 MTU upper bound for interfaces in encap mode #6006

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13 changes: 13 additions & 0 deletions pkg/agent/agent.go
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,14 @@ const (
roundNumKey = "roundNum" // round number key in externalIDs.
initialRoundNum = 1
maxRetryForRoundNumSave = 5
// On Linux, OVS configures the MTU for tunnel interfaces to 65000.
// See https://github.com/openvswitch/ovs/blame/3e666ba000b5eff58da8abb4e8c694ac3f7b08d6/lib/dpif-netlink-rtnl.c#L348-L360
// There are some edge cases (e.g., Kind clusters) where the transport Node's MTU may be
// larger than that (e.g., 65535), and packets may be dropped. To account for this, we use
// 65000 as an upper bound for the MTU calculated in getInterfaceMTU, when encap is
// supported. For simplicity's sake, we also use this upper bound for Windows, even if it
// does not apply.
ovsTunnelMaxMTU = 65000
)

var (
Expand Down Expand Up @@ -1200,6 +1208,11 @@ func (i *Initializer) getInterfaceMTU(transportInterface *net.Interface) (int, e

isIPv6 := i.nodeConfig.NodeIPv6Addr != nil
mtu -= i.networkConfig.CalculateMTUDeduction(isIPv6)
if i.networkConfig.TrafficEncapMode.SupportsEncap() {
// See comment for ovsTunnelMaxMTU constant above.
mtu = min(mtu, ovsTunnelMaxMTU)
}

return mtu, nil
}

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