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Hello everyone,

Today I will share with you MPLS MTU.

An MTU value determines the maximum number of bytes that can be sent each time. If the size of packets exceeds the MTU supported by a transit node or a receiver, the transit node or receiver fragments the packets or even discards them, increasing the network transmission load. MTU values must be correctly negotiated between LSRs to enable packets to successfully reach the receiver.

If an MTU value changes (for example when the local outbound interface or its configuration changes), an LSR recalculates the MTU value and sends a Label Mapping message carrying the new MTU value to all upstream devices.

The relationships between the MPLS MTU and the interface MTU are as follows:
  • If no MPLS MTU is configured on an interface, the interface MTU is used to control the forwarding of MPLS packets.

  • If both an MPLS MTU and an interface MTU are configured on an interface, the smaller value between the two MTUs is used to control the forwarding of MPLS packets.


MPLS has been enabled on the interface using the mpls (interface view) command.


After the mpls mtu command is run, LDP compares the MPLS MTU and the interface MTU, and uses the smaller value between the two MTUs.


# Set the MPLS MTU to 1500 bytes on VLANIF100.

<HUAWEI> system-view

[HUAWEI] interface vlanif 100

[HUAWEI-Vlanif100] mpls

[HUAWEI-Vlanif100] mpls mtu 1500

That is all I want to share with you!

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