label advertise

Function

The label advertise command enables the egress node to advertise labels of a specified type to the penultimate hop.

The undo label advertise command restores the default setting.

By default, the egress node assigns implicit null labels to the penultimate hop.

Format

label advertise { explicit-null | implicit-null | non-null }

undo label advertise

Parameters

Parameter	Description	Value
explicit-null	Disables Penultimate Hop Popping (PHP) and enables the egress node to assign explicit null labels to the penultimate hop.	The value of the explicit null label is 0.
implicit-null	Enables PHP and enables the egress node to assign implicit null labels to the penultimate hop.	The value of the implicit null label is 3.
non-null	Disables PHP and enable the egress node to assign normal labels to the penultimate hop.	The value is equal to or greater than 16.

Views

MPLS view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

MPLS transmits packets along label switched paths (LSPs). The egress at the last hop on the LSP removes MPLS labels from packets before forwarding the packets over IP links or using next layer labels. MPLS labels are useless at the last hop on an LSP. Therefore, penultimate hop popping (PHP) can be configured to enable the penultimate hop to remove labels, which improves forwarding efficiency.

By default, PHP is enabled, and the egress assigns implicit-null labels to the penultimate hop. To specify the type of label that the egress assigns to the penultimate hop, run the following commands:

In a bidirectional association LSP scenario, run the label advertise non-null command to enable the egress to assign a normal label to the penultimate hop.
In an MPLS QoS scenario, run the label advertise explicit-null command to enable the egress to assign an explicit null label to the penultimate hop.

Prerequisites

MPLS has been enabled globally using the mpls (system view) command in the system view.

Precautions

After the label advertise command is run to specify a label, the egress on a newly established LDP LSP or constraint-based routed label switched path (CR-LSP) assigns the specified label to the penultimate hop. The label advertise command can take effect on existing LDP LSPs or CR-LSPs when one of the following conditions is met:

A master/slave main control board switchover is performed.
The reset mpls ldp command is run to reset an LDP public instance for an LDP LSP.
If a CR-LSP is established, the reset mpls rsvp-te command is run to reset Resource Reservation Protocol-Traffic Engineering (RSVP-TE), or the reset mpls te tunnel-interface tunnel command is run to restart a specified TE tunnel.

If the label advertise command is run more than once, the latest configuration overrides the previous one.

Example

# Configure the egress node to assign explicit null labels to the penultimate hop.

<HUAWEI> system-view
[HUAWEI] mpls
[HUAWEI-mpls] label advertise explicit-null