JN0-650 Practice Questions

OSPF determines the best path to a destination by calculating the metric (cost) of each link. By default, Junos OS uses a reference bandwidth of 100 Mbps to calculate this cost using the formula:

When the reference bandwidth is left at the default 100 Mbps, any interface with a speed of 100 Mbps or higher (including 1 GbE and 10 GbE) is assigned a cost of 1 because the minimum OSPF cost is 1. This results in equal-cost paths, preventing the router from preferring the faster 10 GbE link.

To ensure 10 GbE interfaces are preferred, you must create a cost differential:

Option A (Reference Bandwidth): By increasing the reference bandwidth to 10G (or higher), the calculation changes. For a 10 GbE link, the cost becomes $10,000 / 10,000 = 1$. For a 1 GbE link, the cost becomes $10,000 / 1,000 = 10$. Since OSPF prefers the path with the lowest cumulative cost, the 10 GbE link is now preferred.

Option D (Manual Metric): You can manually override the automatic cost calculation by assigning a higher metric specifically to the 1 GbE interfaces. If a 1 GbE interface is manually set to a cost of 50 and the 10 GbE interface remains at 1 (or is set to a lower value), the router will prioritize the 10 GbE path.

Option B is incorrect because a higher metric makes a path less preferred. Option C is incorrect because a 1G reference bandwidth would still result in both 1 GbE and 10 GbE interfaces having a cost of 1.

The exhibit shows the output of the command show route protocol bgp on router R1 for the prefix 172.16.10.1/32. To determine the correct characteristics of this route, we analyze the specific BGP attributes and next-hop information provided in the routing table entry:

Multipath Parameter (Option B): The routing table shows two distinct paths for the prefix 172.16.10.1/32. The first path has two next hops (192.168.10.1 and 192.168.20.1) and is marked with the plus symbol (+) and the asterisk (*), indicating it is both an active and the best route. The presence of multiple next hops being used simultaneously for a single BGP path is a clear indication that the multipath parameter is enabled in the BGP configuration. In Junos OS, BGP multipath allows the installation of multiple equal-cost BGP paths into the forwarding table to facilitate load balancing.

Available Next Hops (Option C): The output explicitly lists two functional next hops for the active path: 192.168.10.1 via ge-1/0/0.2 and 192.168.20.1 via ge-1/0/1.3. Both show an outgoing interface, confirming that this route has two next hops available for traffic forwarding.

IBGP vs. EBGP (Option A): The BGP routes shown have an AS path of 200 I. This indicates the routes were learned from an external Autonomous System (AS 200). Furthermore, the protocol preference is 170. In Junos OS, the default preference for External BGP (EBGP) is 170, whereas the default preference for Internal BGP (IBGP) is 200. Therefore, this configuration is for EBGP, not IBGP.

Hidden Next Hops (Option D): The summary line at the top of the exhibit mentions that there are "2 hidden" routes in the inet.0 table. However, these hidden routes are not the next hops for the 172.16.10.1/32 prefix. A hidden route is a prefix that was rejected by policy or has an unreachable next hop; it is not a "hidden next hop" belonging to an active route.

In a standard campus deployment on Juniper EX Series switches involving VoIP phones and 802.1X authentication, understanding the default behavior of Junos OS 24.4 is critical:

Voice VLAN (Option A): By default, an access port belongs to a single VLAN (the native or data VLAN). For an IP phone to operate correctly on the same physical port as a PC, a Voice VLAN must be explicitly configured and associated with the interface. This allows the switch to segregate voice traffic (usually tagged) from data traffic (untagged).

802.1X Configuration (Option D): Access ports do not have 802.1X authentication enabled by default. To enforce network access control for the client PCs, you must manually enable and configure the dot1x protocol on all relevant interfaces.

PoE Default (Option B): On EX Series switches that support PoE (like P or MP models), PoE is enabled by default on all PoE-capable ports. Therefore, additional configuration is generally not required unless you need to change power priorities or management modes.

LLDP Default (Option C): Standard LLDP is typically enabled by default in the factory configuration of most EX Series switches to facilitate neighbor discovery. While LLDP-MED is used for VoIP, the core requirement for "deploying" the described environment highlights the manual steps of VLAN and security setup rather than protocol discovery which often runs out-of-the-box.