In Junos OS, issuing the rollback 0 command reverts the candidate configuration to the last committed configuration. If you have made changes to some interfaces but have not committed those changes, using rollback 0 will discard these uncommitted changes, reverting to the state of the configuration at the time of the last commit. This command does not affect system files like messages.log, reboot the device, or load the factory default configuration; it simply undoes uncommitted changes.

The Routing Engine (RE) in Juniper Networks devices plays a pivotal role in the control plane, handling tasks that are critical for the operation and management of the network. One of its key functions is processing management traffic, which includes user commands, system configuration, and monitoring operations. The RE also maintains routing tables, which are essential for network routing decisions. These tables contain network topology information and routing paths, which the RE uses to update the Packet Forwarding Engine (PFE) so that it can forward packets appropriately. The RE does not forward transit traffic or process Class of Service (CoS) marked traffic, as these tasks are handled by the PFE.

In the context of VLANs (Virtual Local Area Networks) on a Juniper switch, the numerical values assigned to each VLAN, such as those for Prod, Test, and Dev, are known as VLAN tags. These tags are part of the 802.1 Q VLAN standard, which allows multiple VLANs to coexist on a single physical network. Each tag uniquely identifies the VLAN to which a frame belongs, enabling the switch to segregate and manage traffic based on VLAN membership. This tagging mechanism allows for efficient traffic separation and management, ensuring that devices within one VLAN do not receive traffic intended for another, thus maintaining network security and efficiency.

When multiple users are configuring a Junos device using the "configure private" command, each user gets their own candidate configuration (C). This allows for isolated configuration sessions, where changes made by one user do not impact or interfere with the changes made by another user in their private session.

Referring to the exhibit, the presence of the "+" symbol next to the OSPF route for 192.168.100.2/32 indicates that this is the active route being used to forward traffic. The BGP route, although present, does not have the "+" symbol, indicating it is not the active route. In Junos OS, the routing table displays the active route with a "+" symbol, and the fact that the OSPF route has this symbol means it is the preferred path based on the routing protocol's decision process, which takes into account factors such as route preference (administrative distance) and metrics.