Default MPLS Behavior on Junos Devices

AC

MPLS (Multiprotocol Label Switching) is a protocol used in packet-switched networks to provide quality of service (QoS) guarantees, traffic engineering, and virtual private network ( VPN) services.

Here are the correct statements about the default MPLS behavior on Junos devices:

1. The MPLS label is pushed by the ingress router.

When a packet enters an MPLS network, the ingress router assigns an MPLS label to the packet and pushes it onto the label stack. The label identifies the packet's forwarding path through the MPLS network. The ingress router is responsible for determining the label and pushing it onto the packet before forwarding it to the next hop.

2. The MPLS label is popped by the penultimate router.

The penultimate router is the second-to-last router in the MPLS network before the egress router. It is responsible for removing the top MPLS label from the label stack and forwarding the packet to the egress router. The egress router then removes the last MPLS label and forwards the packet to the destination.

Therefore, the correct statements are (C) The MPLS label is pushed by the ingress router and (A) The MPLS label is popped by the penultimate router.

Option (B) is incorrect because the ultimate router (egress router) removes the last MPLS label, not the first.

Option (D) is incorrect because the ingress router assigns the MPLS label and pushes it onto the packet, not swap it with an existing label.