Free Practice Questions for Juniper JN0-364 Exam

Answer : A

In the IS-IS (Intermediate System to Intermediate System) protocol as implemented in Junos OS, the output of operational commands uses specific numerical representations to denote the hierarchy levels of a neighbor adjacency. Understanding these values is crucial for troubleshooting peering relationships in a multi-level IS-IS network.

According to Juniper Networks technical documentation, the show isis adjacency command displays the status of the neighbors. The 'L' column indicates the level of the adjacency:

Level 1: Indicates the adjacency is strictly for intra-area routing.

Level 2: Indicates the adjacency is strictly for backbone/inter-area routing.

Level 3: This is a shorthand representation used by Junos to indicate that a single adjacency has been established for both Level 1 and Level 2 simultaneously.

The critical distinction in this question lies in the interface type. On a broadcast interface (such as standard Ethernet), IS-IS typically establishes and maintains separate adjacencies for Level 1 and Level 2. In the CLI output for a broadcast link, you would generally see two separate lines for the same neighbor---one for Level 1 and one for Level 2.

However, on a point-to-point (P2P) interface, IS-IS can negotiate both levels within a single adjacency. When this occurs, Junos consolidates the output into a single entry and uses Level 3 to signify that the adjacency is functional for both levels. Since the exhibit shows ge-0/0/0.0 as Level 3, it confirms that the link is configured with a point-to-point encapsulation (either natively or via the interface-type p2p command) and is acting as a Level 1/2 adjacency.

Option B is incorrect as the number '3' refers to protocol levels, not the count of neighbors. Option C is a reference to data center architectures that does not influence IS-IS level nomenclature. Option D is incorrect because, as noted, broadcast interfaces display these levels separately rather than using the Level 3 shorthand.

Answer : A

In Juniper Networks Junos OS, the Label Distribution Protocol (LDP) is specifically designed to automate the creation of Label Switched Paths (LSPs) based on the information provided by the underlying Interior Gateway Protocol (IGP), such as OSPF or IS-IS. When LDP is enabled on a set of interfaces within an OSPF area (as shown in the exhibit with Area 0.0.0.0), it automatically discovers neighbors and exchanges label mappings for all known unicast routes in the routing table.

The defining characteristic of LDP in this context is its 'topology-driven' nature. Unlike RSVP (Resource Reservation Protocol), which typically requires the manual configuration of each LSP ingress point and destination, LDP follows the IGP's shortest path tree to automatically build a full mesh of LSPs between all participating routers. This means that every Provider Edge (PE) and Provider (P) router in the exhibit---PE1, PE2, PE3, P1, P2, and P3---will establish label-switched connectivity to every other router without the administrator having to define individual tunnels.

LDP accomplishes this through a downstream-unsolicited label distribution mode by default in Junos. Each router assigns a local label for its loopback address and other prefixes and advertises these to its neighbors. Because every router is performing this action for every reachable prefix in the OSPF domain, a complete fabric of label-switched paths is formed. While RSVP is more robust for traffic engineering and bandwidth reservation, LDP is the preferred protocol for creating a simple, scalable full mesh of LSPs for applications like Layer 3 VPNs or internal BGP tunneling where complex path manipulation is not required. BFD is a failure detection protocol, and BGP is used for service signaling, making LDP the only correct choice for automatic mesh creation.

Answer : B

In the IS-IS (Intermediate System to Intermediate System) protocol, communication between routers is performed using Protocol Data Units (PDUs). To discover neighbors and maintain adjacencies, IS-IS relies on the Hello PDU (IIH - IS-IS Hello).

According to Juniper Networks technical documentation, when IS-IS is enabled on an interface, the router begins transmitting Hello PDUs to a multi-destination address (multicast). These PDUs contain essential information such as the router's System ID, its configured Area Addresses, and its Level capability (Level 1, Level 2, or both). For two routers to become neighbors, they must exchange these Hello PDUs and agree on specific parameters, such as the MTU of the link and the hello/hold timers.

Once an adjacency is established, the Hello PDU serves as a 'keepalive' mechanism. If a router stops receiving Hello PDUs from a neighbor for a duration exceeding the Holding Time, it assumes the neighbor is down and flushes the associated Link-State PDUs (LSPs) from its database.

To clarify the other options:

Link-State PDU (Option A): These are used to distribute actual topology and reachability information, not to form adjacencies.

Partial Sequence Number PDU (Option C): PSNPs are used on point-to-point links to acknowledge the receipt of LSPs or to request missing LSPs.

Update PDU (Option D): This is not a standard IS-IS term; in IS-IS, updates are handled via the flooding of LSPs.

Answer : A, B

In Junos OS, a static route is a manually configured entry in the routing table. Unlike dynamic routes, which have built-in timers and aging mechanisms, static routes are generally 'permanent' as long as their conditions for validity are met.

1. Manual Removal (Option A):

Since static routes are explicitly defined by the administrator, the most direct way to remove one is through a configuration change. Using the delete routing-options static route command followed by a commit will immediately remove the route from the Routing Information Base (RIB).

2. Next-Hop Reachability (Option B):

For a static route to be 'active' and installed in the forwarding table, its next-hop must be reachable. If a static route points to a specific physical interface or an IP address on a local segment, and that outbound interface becomes unavailable (e.g., the link goes 'Down'), the Junos kernel detects that the next-hop is no longer viable. Consequently, the route is marked as 'hidden' or 'inactive' and is removed from the active forwarding table to prevent traffic from being black-holed.

Why other options are incorrect:

Aging (Option C): Static routes do not have an expiration timer based on traffic. Even if no packet is sent for years, the route remains as long as the interface is up.

Remote Reachability (Option D): Standard static routes only track the status of the local interface or the immediate next-hop. They do not possess 'end-to-end' visibility. If a host two hops away fails, the local router has no way of knowing this via the static route itself. To achieve this level of tracking, features like RPM (Real-time Performance Monitoring) or BFD (Bidirectional Forwarding Detection) must be linked to the static route.

Answer : A

To determine which traffic is being sent through a tunnel in a Junos OS environment, an administrator must analyze the routing table output for the exit interface associated with each destination prefix. The provided exhibit shows the results of the show route command on router R2 for two specific destination networks.

In the first output, the destination 198.51.100.1/32 is an active static route. The next-hop information specifies that traffic for this address is sent to the gateway 203.0.113.65 via the interface ge-0/0/3.0. According to Juniper Networks interface naming conventions, the prefix ge- denotes a Gigabit Ethernet interface, which represents a standard physical connection. Therefore, this traffic does not traverse a tunnel.

In the second output, the destination 172.20.110.0/24 is also an active static route. However, the next-hop for this network is listed as via gr-0/0/0.0. In the Junos operating system, the gr- prefix explicitly identifies a Generic Routing Encapsulation (GRE) tunnel interface. GRE is a widely used protocol in service provider networks to encapsulate various network layer protocols over an IP backbone, effectively creating a virtual point-to-point link. Because the routing table has installed the route for 172.20.110.0/24 specifically via the gr- interface, all traffic destined for this network will be encapsulated and sent through the tunnel.

The other choices are incorrect for the following reasons:

203.0.113.65 (Option B): This is the next-hop IP address for the physical Gigabit Ethernet path; it is not a destination network directed to a tunnel.

0.0.0.0/0 (Option C): There is no information in the exhibit regarding a default route.

198.51.100.1/32 (Option D): As identified by the ge- interface prefix in the exhibit, traffic for this destination is sent via a physical Ethernet link.