Get Juniper JN0-364 Exam Practice Questions - Real and Updated

Answer : D

When designing High Availability (HA) for Juniper Service Provider routers, understanding the interaction between the control plane and data plane is vital. The user has already enabled Graceful Routing Engine Switchover (GRES), which synchronizes the interface and kernel state between the primary and backup Routing Engines (REs). However, GRES by itself does not preserve the routing protocol state (like OSPF adjacencies or BGP sessions).

To achieve the preservation of the routing protocol state without relying on external 'helper' routers, you must implement Non-Stop Active Routing (NSR). According to Juniper Networks documentation, NSR uses the infrastructure provided by GRES to also synchronize the routing protocol process (rpd) information. Under NSR, the backup RE maintains a 'hot' standby state of all routing protocols. If the primary RE fails, the backup RE takes over immediately. Because it already possesses the full routing table and peer session states, the peering neighbors are unaware that a switchover occurred. No protocol adjacency resets occur, and traffic continues to flow uninterrupted.

It is crucial to differentiate NSR from Graceful Restart (Option C). While Graceful Restart also aims to maintain traffic flow during a switchover, it does require help from neighboring routers (known as 'helper mode'). If the neighbors do not support or are not configured for Graceful Restart, the sessions will drop. Since the user explicitly stated they want to 'avoid relying on helper routers,' Graceful Restart is not the correct solution.

Non-stop Active Bridging (Option A) provides a similar 'hitless' failover but specifically for Layer 2 environments (STP/VLANs) rather than Layer 3 routing protocols. BFD (Option B) is a failure detection protocol used to speed up convergence but does not preserve state during an RE failover; in fact, without NSR, BFD would likely trigger a faster teardown of the session during a switchover. Therefore, NSR is the only feature that meets the requirement for independent control-plane preservation.

Answer : B

In the Juniper Networks Junos operating system, the management of routing information is partitioned into several distinct routing tables (RIBs), each serving a specific architectural purpose. When dealing with Multiprotocol Label Switching (MPLS), understanding the distinction between inet.0 and inet.3 is fundamental for troubleshooting and traffic engineering.

The inet.3 routing table is specifically designed to store the egress IPv4 addresses of Label-Switched Paths (LSPs). When an ingress router successfully establishes an LSP (via RSVP or LDP), it places the host address of the egress router (the tail-end) into the inet.3 table. This table is not used for general packet forwarding; instead, it is primarily used by the Border Gateway Protocol (BGP) for next-hop resolution. When BGP receives a route, it checks both inet.0 and inet.3 to resolve the next hop. If a matching entry exists in inet.3, the router knows it can reach that destination via an MPLS tunnel, allowing for the encapsulation of BGP traffic within MPLS.

In contrast, inet.0 is the default unicast routing table used for standard IPv4 forwarding and contains routes learned via IGPs (OSPF, IS-IS) or static routing. inet.1 is utilized for multicast forwarding (MBGP), and inet.2 is typically used for Multicast Source Discovery Protocol (MSDP) or RPF checks in multicast environments. By isolating LSP egress points in inet.3, Junos prevents MPLS-specific paths from interfering with standard IGP path selection unless the administrator explicitly chooses to merge them (e.g., using the traffic-engineering bgp-igp command). Therefore, by default, the ingress router maintains its list of reachable LSP endpoints in inet.3.

Answer : A

When troubleshooting OSPF in a service provider environment, distinguishing between 'stuck' adjacencies and 'flapping' adjacencies is the first step. A session that transitions frequently between Full and Down indicates that the relationship can be established successfully (meaning parameters match), but it cannot be maintained.

According to Juniper Networks documentation, the most common cause for a session to drop from Full to Down is the expiration of the Dead Interval. If a router does not receive a Hello packet within the Dead Interval (usually 40 seconds), it tears down the adjacency. A physical interface flapping (Option A) is the primary trigger for this. If the physical link or the underlying transport (like a leased line or a microwave link) goes down even momentarily, the OSPF process immediately detects the interface failure, flushes the neighbors, and moves the state to Down. As soon as the interface comes back up, the routers perform the Hello exchange and reach the Full state again, creating the flapping cycle.

Analysis of other options:

MTU Mismatch (Option D): This typically causes the adjacency to get 'stuck' in the Exchange or ExStart state. The routers can exchange small Hello packets, but when they try to send larger Database Description (DBD) packets that exceed the MTU, the packets are dropped, preventing the session from ever reaching 'Full.'

Area ID Mismatch (Option C): This prevents the adjacency from even reaching the Init state; the routers will never form a neighbor relationship.

Route Preference (Option B): This affects which route is chosen for the forwarding table but has no impact on the OSPF neighbor state machine itself.

Answer : D

In a Segment Routing (SR-MPLS) architecture using IS-IS as the control plane, routers exchange labels (segments) to build Label-Switched Paths (LSPs) without the need for traditional signaling protocols like LDP or RSVP. According to Juniper Networks technical documentation, for a router to be reachable via a shortest-path LSP from other nodes in the network, it must advertise a Prefix Segment Identifier (Prefix SID).

A specific type of Prefix SID is the Node SID, which is assigned to a loopback address (typically lo0.0) to uniquely identify the router within the SR domain. In the provided exhibit, router R10 has been configured with a Segment Routing Global Block (SRGB) starting at label 300000. This configuration tells the router which label range to use for global segments, but it does not automatically assign a label to its own loopback interface.

Without a Node SID configuration, R10 is not telling its neighbors which specific index or label within that SRGB corresponds to its own address. Consequently, the other nine routers in the IS-IS area can calculate the shortest path to R10 using standard SPF, but they cannot perform the 'label-binding' necessary to push an SR-MPLS label onto the packets.

To solve this, a Node SID must be explicitly configured under the loopback interface within the IS-IS protocol hierarchy, such as:

set protocols isis interface lo0.0 level 2 ipv4-node-sid index <value>

Analysis of incorrect options:

Binding SID (Option A): This is used to encapsulate or steer traffic into a specific policy or tunnel (like a TE-LSP) and is not required for basic shortest-path reachability.

Adjacency SID (Option B): These are generated automatically by Junos for each link and represent a specific local hop; they are not used for global 'shortest-path' forwarding to a distant node.

BGP Prefix SID (Option C): This is used for BGP Egress Peer Engineering (EPE) or prefix advertisement via BGP, which is not relevant for building the underlying IS-IS SR-MPLS transport.

Therefore, configuring an explicit IPv4 node SID is the mandatory step to enable the rest of the network to build a shortest-path SR-LSP toward R10.

Answer : A, B, E

One of the most significant architectural improvements in IPv6 is the move from a complex, variable-length header (as seen in IPv4) to a streamlined, fixed-length base header of 40 bytes. Additional functionality that was previously handled by 'Options' in IPv4 is now moved to Extension Headers, which are inserted between the IPv6 base header and the upper-layer protocol (TCP/UDP).

According to Juniper Networks technical documentation and RFC 8200, the following are valid IPv6 Extension Headers:

Hop-by-Hop Options (Option B): This header carries optional information that must be examined by every node along the delivery path. It is used for features like the Router Alert and Jumbo Payload options.

Fragment (Option E): Unlike IPv4, where any router can fragment a packet, in IPv6, fragmentation is performed only by the source node. The Fragment header contains the information necessary for the destination to reassemble the packet (Offset, Identification, and More Fragments flag).

Destination Options (Option A): This header carries information intended only for the destination node. It can appear twice: once before a routing header and once after.

Why other options are incorrect:

Protocol (Option C): In IPv4, this was a field in the header. In IPv6, this is replaced by the Next Header field, which identifies the type of the following header (whether it's an extension header or the upper-layer protocol).

Header Checksum (Option D): This field was entirely removed in IPv6. IPv6 relies on the data link layer (Ethernet) and the transport layer (TCP/UDP) to perform error detection, significantly reducing the processing overhead for routers in the core of a service provider network.