Huawei AR1200 Series - Configuring an MPLS MTU on an Interface

remote-peer auto-dod-request
The function of triggering a request to a downstream node for a label mapping message
associated with all remote LDP peers with a specified LSR ID in DoD mode.
----End
2.5.6 Configuring an MPLS MTU on an Interface
An MPLS MTU can be configured on an interface to determine the maximum size of MPLS
packets that can be forwarded each time.
Context
MTU is short for maximum transmission unit. An MTU value determines the maximum number
of bytes each time a sender can send. 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, aggravating the network transmission load. MTU values must be correctly negotiated
between LSRs to allow packets to successfully reach the receiver.
LDP MTU = Min { All MTUs advertised by downstream devices, Local outbound interface
MTU }
A downstream LSR uses the preceding formula to calculate an MTU value, adds it to the MTU
TLV in a Label Mapping message, and sends the Label Mapping message upstream.
If an MTU value changes (such as when the local outbound interface or its configuration is
changed), an LSR recalculates an MTU value and sends a Label Mapping message carrying the
new MTU value upstream. The comparison process repeats to update MTU information along
an LSP.
The relationships between the MPLS MTU and the interface MTU are as follows:
l If an interface MTU but not an MPLS MTU is configured on an interface, the interface
MTU is used.
l If both an MPLS MTU and an interface MTU are configured on an interface, the smaller
value between the MPLS MTU and the interface MTU is used.
Procedure
Step 1 Run:
system-view
The system view is displayed.
Step 2 Run:
interface interface-type interface-number
The view of an MPLS-enabled interface is displayed.
Step 3 Run:
mpls mtu mtu
An MPLS MTU is configured on the interface.
Huawei AR1200 Series Enterprise Routers
Configuration Guide - MPLS 2 MPLS LDP Configuration
Issue 01 (2011-12-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
43