(Optional) Configuring PHP

Penultimate hop popping (PHP) can be configured on the egress to allocate a label to an LSR at the penultimate hop, helping relieve the burden on the egress.

Context

No label needs to be swapped on the egress of an LSP. PHP can be configured on the egress to allow the LSR at the penultimate hop to pop out the label from an MPLS packet and send the packet to the egress. After receiving the packet, the egress directly forwards the unlabeled IP packet or the single-labeled packet. PHP helps reduce the burden on the egress.

Procedure

Access the system view.
```
system-view
```
Access the MPLS view.
```
mpls
```
Configure the label allocated to the LSR at the penultimate hop.
```
label advertise { explicit-null | implicit-null | non-null }
```
TOne of the following parameters can be configured in this command:
- implicit-null: is the default value and means that PHP is supported. If this parameter is configured, the egress allocates an implicit null label with the value of 3 to the LSR at the penultimate hop.
- explicit-null: means that PHP is not supported. If this parameter is configured, the egress allocates an explicit null label with the value of 0 to the LSR at the penultimate hop. The explicit-null parameter can be configured when MPLS QoS attributes are used.
- non-null: means that PHP is not supported. If this parameter is configured, the egress allocates a common label with a value greater than or equal to 16 to the LSR at the penultimate hop.
Exercise caution when using the explicit-null or non-null parameter. The setting leads to a great deal of resource consumption on the egress.

PHP takes effect on LSPs that will be established after PHP is configured.