The "ultimate-hop-popping" term refers to the action taken by the penultimate router in an LSP to remove the MPLS label before delivering the packet to the ultimate router,which is not desired here. Configuring the "explicit-null" statement causes the penultimate router to replace the top label with a label that has a value of 0, which instructs the ultimate router to perform a label lookup and preserve the label switching for the entire LSP.

References:

• Juniper Networks documentation on MPLS: MPLS Applications User Guide for Routing Devices

In segment routing, SIDs (Segment Identifiers) are used to identify different types of segments that can be traversed. A node SID represents an instruction to route a packet to a particular node, and an adjacency SID represents an instruction to route a packet over a specific link or adjacency between two nodes.

References

• Juniper Networks Technical Documentation on Segment Routing

In the given exhibit, interfacege-0/0/0is configured to accept VLANs 101-120 andge-0/0/1is configured with flexible VLAN tagging, which means it can tag traffic with any VLAN ID specified. However, only VLAN 200 is explicitly mentioned forge-0/0/1.A. Traffic tagged with VLAN 101 will pass throughge-0/0/0and will egress onge-0/0/1with the same VLAN tag, because the VLAN ID is within the allowed range on both interfaces.B. VLAN 100 is not specified in the allowed VLAN range forge-0/0/0(which is 101-120),nor is it specified underge-0/0/1. Therefore, it will be dropped.References:

• Understanding VLAN Tagging, Juniper TechLibrary
• Configuring VLANs for EX Series Switches, Juniper TechLibrary