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Routing & Switching · Advanced

Penultimate Hop Popping (PHP)

The MPLS behavior where the next-to-last router removes the top label so the egress router does only one lookup.

Definition

The egress router advertises implicit null (label 3) to request PHP. Explicit null (label 0) can be advertised instead to keep the Traffic Class bits for QoS on the last hop.

Example

mpls ldp explicit-null

Exam tip

Use explicit null when the egress needs EXP markings for QoS.

Related terms