Update messages are exchanged between BGP peers in the Established state to advertise new routes, withdraw previously advertised routes, and share path attributes for reachable prefixes.
Notification messages are used to signal errors detected in the BGP session and immediately terminate the session when a protocol error occurs.

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.

A route being hidden in BGP usually indicates a configuration that prevents it from being used, such as a next-hop that is not reachable.
B). Configuring a routing policy on R1 that sets the next-hop to the address used for IBGP peering ensures reachability of the next-hop within the local AS. D. Applying the correct routing policy as an export policy to the IBGP group on R1 will share the route with the IBGP peers, in this case, R2 and R3.

In the IPv6 architecture, the base header is kept at a fixed size of 40 bytes to streamline processing. Any additional features or options are handled byExtension Headers, which are inserted between the IPv6 header and the upper-layer protocol. According to Juniper Networks technical documentation and RFC 8200, when a source node needs to list one or more intermediate nodes to be "visited" on the way to the final destination, it utilizes theRouting extension header (Option B).
The Routing header is functionally similar to the "Source Route" option in IPv4. When a packet contains a Routing header, it is addressed to the first intermediate node listed in the header. That node examines the header, swaps its own address with the next address in the list, and forwards the packet. This process continues until the packet reaches the final destination. This is a foundational component for technologies like Segment Routing over IPv6 (SRv6), where the Routing header (specifically the Segment Routing Header or SRH) is used to steer traffic through a specific set of service instructions or nodes.
To distinguish this from the other options:
* Hop-by-hop options (Option A):These carry information that must be examined byeverynode along the path (such as Router Alert), not just specific intermediate nodes.
* Fragment (Option C):This is used only when the source node needs to fragment a packet that exceeds the path MTU.
* Destination options (Option D):These carry optional information intended specifically for the destination node (or nodes listed in a Routing header), but they do not dictate the path themselves.

The routing table shows two equal-cost next hops for the prefix and both are installed in the forwarding table, which means the router is selecting both next hops for forwarding traffic. This indicates equal-cost multipath forwarding.
The forwarding table entry shows a load-balancing group containing both next hops, which reflects the default Junos behavior of performing load balancing across equal-cost paths when multiple next hops exist for the same route.