OSPF internal = 10 OSPF external = 150
Some vendors have a preference (distance) of 20 for external BGP (EBGP) and a distance of 200 for internal BGP (IGBP). Junos OS uses the same value (170) for both EBGP and IBGP.
However, this difference between vendors has no operational impact because Junos OS always prefers EBGP routes over IBGP routes.

The configuration exhibit demonstrates a classic scenario where mismatched static routing leads to a routing loop. Router R1 is configured with a default route (0.0.0.0/0) pointing to R2 as its next hop. Conversely, R2 is configured with a broad static route for 10.1.0.0/16 pointing back to R1.
If a user sends a packet to an unassigned IP address such as 10.1.99.1, the following sequence occurs:
R1 receives the packet and consults its routing table. Finding no specific match for the 10.1.99.1 host, it uses the default route and forwards the packet to R2.
R2 receives the packet and identifies that 10.1.99.1 falls within its defined static route for
10.1.0.0/16.
Following its configuration, R2 forwards the packet back to R1. This process repeats indefinitely-- or until the packet's Time to Live (TTL) reaches zero--because the broad summary on R2 encompasses addresses that R1 does not actually have a local path for. This illustrates the critical importance of ensuring that summary routes or default routes do not overlap in a way that creates circular forwarding paths for non-existent destinations.

In the Junos OS architecture, the routing table often receives prefix information from various sources, including direct connections, static configurations, and multiple dynamic interior and exterior gateway protocols. Route preference, frequently referred to as administrative distance in other vendor environments, serves as the primary tie-breaking mechanism used by the Routing Engine to select a single "active" route when multiple entries for the exact same destination prefix exist from different protocol sources. Each routing source is assigned a default numerical value, where a lower numerical value indicates a more preferred or "trustworthy" source. For instance, a direct route typically carries a preference of 0, while OSPF internal routes default to 10 and BGP routes default to 170.
The selection process evaluates these values; the route with the lowest preference is installed in the forwarding table and used for transit traffic. If preferences are equal, Junos secondary tie- breakers like local preference or metric are considered. Understanding this hierarchy is critical for traffic engineering and ensuring predictable routing behavior across the fabric. Modification of these default values via routing policy allows administrators to influence path selection without altering the underlying protocol metrics themselves.

In the Junos OS architecture, maintaining visibility into the health of the Routing Engine (RE) is paramount for ensuring control plane stability. The command show chassis routing-engine is the primary tool for a high- level hardware status overview. It provides critical telemetry regarding the RE ' s current CPU utilization (broken down by user, background, and kernel tasks), memory usage statistics, and uptime. This command is essential for identifying if the device ' s " brain " is under significant stress due to heavy protocol processing or management tasks.
For a more granular, process-specific analysis, the show system processes extensive command is utilized.
Similar to the ' top ' utility in Unix-based systems, it lists all active software daemons (such as rpd for routing, dcd for interfaces, and mgd for management) and ranks them by their real-time CPU and memory consumption. This allows an architect to pinpoint exactly which process might be causing a performance bottleneck. While show chassis environment focuses on physical hardware health like temperatures and fan speeds, and resource-monitor provides summary data, the combination of show chassis routing-engine and show system processes extensive offers the most comprehensive diagnostic view of the device ' s internal computational resources. Reference: Operational Monitoring and Maintenance, System Health Monitoring.

Junos OS can store up to 50 rollback configuration files, making B the correct answer. These rollback files allow administrators to revert to previous configurations, providing a safety net that facilitates recovery from configuration errors or undesired changes.