(Optional) Configuring the MPLS MTU of an Interface

An MPLS MTU can be configured on an interface to determine the maximum number of bytes in an MPLS packet that a device can forward without fragmenting the MPLS packet.

Context

LDP selects the minimum value among MTUs on all outbound interfaces of an LSP. MPLS use the minimum MTU to determine the maximum size of each MPLS packet that can be forwarded without being fragmented. The MPLS MTU helps prevent forwarding failures on transit nodes.

The dependency between an MPLS MTU and an interface MTU is as follows:

If an interface MTU is set and no MPLS MTU is set on an interface, the interface MTU is used.
If both an MPLS MTU and an interface MTU are set on an interface, the smaller value between the MPLS MTU and the interface MTU is used.

The MPLS MTU of an interface can take effect only after the MTU signaling is enabled.

Procedure

Run system-view
The system view is displayed.
Run interface interface-type interface-number
The view of the interface enabled with MPLS is displayed.
Run mpls mtu mtu
An MPLS MTU is set for an interface.
(Optional) Run interface-mtu check-mode { ip | label-contained-length }slot slot-id
An interface MTU check mode is configured.
Choose a check mode based on scenarios:
- ip: applies to IP forwarding scenarios.
- label-contained-length: applies to MPLS forwarding scenarios.
The device checks a packet's size based on the configured check mode and fragments a packet if its size exceeds the interface MTU.

In VS mode, this command is supported only by the admin VS.
Run commit
The configurations are committed.