Comprehensive and Detailed In-Depth Explanation:
* In MPLS (Multiprotocol Label Switching), label 0 is a special label known as the Implicit Null Label.
* If an LSR (Label Switching Router) finds that the label to be swapped is 0, it performs PHP (Penultimate Hop Popping), meaning:# The label is removed (popped) from the MPLS packet.# The IP packet is forwarded to the next hop without an MPLS label.# This optimization reduces label processing overhead at the egress router.
# Reference: HCIP-Datacom Advanced Routing & Switching Technology - MPLS Label Processing & PHP Mechanism