Changed JN0-364 Exam Questions

In Junos OS, astatic routeis 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, itsnext-hop must be reachable. If a static route points to a specific physical interface or an IP address on a local segment, and thatoutbound 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 likeRPM (Real-time Performance Monitoring)orBFD (Bidirectional Forwarding Detection)must be linked to the static route.

When transitioning to an IPv6 environment usingOSPFv3(the version of OSPF designed for IPv6), there are significant architectural differences compared to OSPFv2 (IPv4). According to Juniper Networks technical documentation, OSPFv3 was redesigned to be more protocol-agnostic.

Router ID (Option C):

Despite OSPFv3 routing IPv6 (which uses 128-bit addresses), the OSPFRouter IDremains a32-bit valueformatted like an IPv4 address (e.g., 1.1.1.1). This is a common point of confusion. In a pure IPv6 environment where no IPv4 addresses are configured on any interfaces, a Juniper router cannot automatically derive a Router ID. Therefore, the administrator must manually configure a 32-bit Router ID under [edit routing-options] for the OSPFv3 process to initialize.

Interface Configuration (Option D):

OSPFv3 runs directly over the IPv6 link-local scope. Unlike OSPFv2, it does not require an IPv4 address to function. Therefore, interfaces areonly required to be configured with family inet6(Option D). You do not need "dual-stack" (both IPv4 and IPv6) functionality just to run OSPFv3. The protocol uses the link-local address (fe80::/10) of the interface for neighbor adjacencies and as the next hop for routing updates. This separation allows OSPFv3 to carry multiple "address families" (both IPv4 and IPv6 unicast) if needed, but the base requirement for an IPv6-only network is simply the family inet6 configuration.

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 routerR2for two specific destination networks.

In the first output, the destination198.51.100.1/32is 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 interfacege-0/0/3.0. According to Juniper Networks interface naming conventions, the prefixge-denotes aGigabit Ethernetinterface, which represents a standard physical connection. Therefore, this traffic does not traverse a tunnel.

In the second output, the destination172.20.110.0/24is also an active static route. However, the next-hop for this network is listed asvia gr-0/0/0.0. In the Junos operating system, thegr-prefix explicitly identifies aGeneric 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 thege-interface prefix in the exhibit, traffic for this destination is sent via a physical Ethernet link.

In Junos OS, the Routing Engine maintains several different tables to manage various types of reachability and forwarding information. When a router is running MPLS, it must track both IP routes and label-to-label mappings.

Thempls.0table is the primary repository for theLabel Information Base (LIB)and theLabel Forwarding Information Base (LFIB). According to Juniper Networks documentation, mpls.0 is used by transit and egress routers to perform label lookups. When a labeled packet arrives at an interface, the router looks at the top label and references the mpls.0 table to determine the next action. This table stores the mapping of incoming labels to their corresponding operations:Pop(remove the label),Swap(replace the label), orPush(add an additional label).

It is crucial to understand the roles of the other tables to avoid confusion:

inet.0 (Option D):This is the default unicast routing table for IPv4, used for standard IP-to-IP forwarding.

inet.3 (Option C):This is theMPLS Path Table. It stores the egress loopback addresses of LSPs and is used by BGP for next-hop resolution to determine if a destination can be reached via an MPLS tunnel. While inet.3 knowsaboutLSPs, the actual label-switching instructions reside in mpls.0.

inet6.0 (Option A):This is the default unicast routing table for IPv6.

Therefore, for the specific purpose of storing the label base used for transit switching operations,mpls.0is the correct and only table used in the Junos architecture.