With penultimate-hop popping (PHP), the penultimate provider switch is responsible for popping the MPLS label and forwarding the traffic to the egress PE switch. The egress PE switch then performs an IP route lookup and forwards the traffic.
Penultimate-hop popping reduces the processing load on the egress PE switch, because it is not responsible for both popping the MPLS label and performing the IP route lookup prior to forwarding the traffic. EX Series switches enable PHP by default with IP over MPLS configurations. You can however change this behavior if required.
For more information, click Junos OS MPLS for EX Series Switches.