JN0-650 Exam Dumps - Juniper JNCIP-ENT Questions and Answers

OSPFv2 (IPv4) and OSPFv3 (IPv6) share many fundamental concepts, such as the SPF algorithm and the use of areas, but they have distinct differences in how they handle prefix information and LSA headers in Junos OS.

Backbone Requirement (Option C):Both OSPFv2 and OSPFv3 utilize a hierarchical structure. In both versions, all areas must connect to a centralArea 0 (the backbone)to allow for inter-area routing. If an area is not physically connected to Area 0, a virtual link must be established.

Flooding Scope (Option D):One of the significant architectural changes in OSPFv3 is the inclusion of theflooding scopedirectly into the LSA header. In OSPFv3, the LS Type field is expanded to 16 bits, where the top three bits define the flooding scope (e.g., Link-local, Area, or AS scope). This allows routers to understand how far an LSA should be propagated without needing to understand the specific LSA type itself.

LSA Prefix Information (Option A):This statement is misleading. In OSPFv2, Router and Network LSAs (Type 1 and 2) carry both topology and prefix information. However, a key design goal of OSPFv3 was toseparatetopology from prefix information. In OSPFv3, Type 1 and 2 LSAs only describe the topology, while prefixes are carried in new LSA types:Intra-Area-Prefix-LSAs(Type 9) andLink-LSAs(Type 8).

Processing (Option B):OSPFv2 is processed "per-subnet" because it forms adjacencies based on IPv4 subnets. OSPFv3 is processed"per-link", meaning it forms adjacencies between interfaces on the same physical link regardless of whether they share a common IPv6 prefix.

For maintenance scenarios where a router must remain operational but should not be used as a transit path for OSPF traffic, Junos OS uses theoverloadfunctionality.

OSPF Overload (Option B):When you enable overload under protocols ospf, the router advertises its own Link-State Advertisements (LSAs) with amaximum metric (65535)for all of its transit links.

Traffic Diversion:Because OSPF uses the Shortest Path First (SPF) algorithm to find the lowest-cost path, other routers in the network will see the overloaded router as an extremely high-cost path. They will calculate alternate routes, effectivelymoving transit traffic off the routerwhile still allowing management traffic directedtothe router's own interfaces.

Timeout Options:You can configure this to be permanent or set a timeout so that the router automatically resumes normal metric advertisements after a set period.

To interoperate with Cisco switches runningPer-VLAN Spanning Tree Plus (PVST+), Juniper devices must useVLAN Spanning Tree Protocol (VSTP).

PVST+ Compatibility:VSTP is specifically designed to handle the per-VLAN BPDU requirements of Cisco's PVST+. It generates a separate spanning tree instance for each VLAN and uses the same multicast destination MAC address as Cisco devices.

Other Protocols:MSTP (B) is used for grouping VLANs into regions; RSTP (D) is a single-instance protocol (IEEE 802.1w) and is generally incompatible with per-VLAN BPDU requirements without additional configuration.

The exhibit illustrates a PIM multicast environment where routerR2has received a multicast packet fromSource 1 (192.168.100.10)on itsge-0/0/4.0interface. To prevent loops, PIM-SM uses a mechanism calledReverse Path Forwarding (RPF).

RPF Check Process (Option A):When a multicast packet arrives, the router performs an RPF check by looking up the source's IP address in itsunicast routing table(typically inet.0).

The exhibit's command output, show multicast rpf 192.168.100.10, explicitly shows that for the source network $192.168.100.0/24$, theRPF interfaceisge-0/0/1.0.

Because the packet actually arrived onge-0/0/4.0instead of the expected ge-0/0/1.0 interface, the RPF check fails.

Packet Discard (Option C):According to standard PIM-SM operation in Junos OS 24.4, if a multicast packet fails the RPF check—meaning it arrived on an interface that the router does not use to reach the source via unicast—the packet isdiscarded. This is a fundamental loop-prevention mechanism that ensures multicast traffic is only accepted from the shortest path toward the source.

Option B is incorrectbecause the router will not add any interfaces to the Outgoing Interface List (OIL) for a packet that fails the initial RPF check.

Option D is incorrectbecause the exhibit clearly shows the interface in the RPF table (ge-0/0/1.0) is different from the interface where the packet was received (ge-0/0/4.0).

When a peer incorrectly floods your router with an excessive number of routes, it can exhaust system resources and crash the routing engine.

Prefix-Limit (Option B):The prefix-limit (or accepted-prefix-limit) parameter is the primary defense against such "route leaks".

You can set amaximum thresholdfor the number of prefixes allowed from a specific BGP neighbor or group.

When the limit is reached, Junos can be configured to either just log a warning ortear down the BGP sessionentirely (using the teardown keyword) to protect the router.

This prevents the "hundreds of thousand routes" from ever being fully processed or installed into the main routing table.

Damping (Option A):Damping is used to suppress unstable, "flapping" routes, but it does not limit the total volume of stable routes received.

The exhibit shows a network topology whereMultiple VLAN Registration Protocol (MVRP)is used to dynamically manage VLANs across switches Core-1, Access-1, and Access-2.

Identifying the Missing Configuration:According to the diagram, the trunk link betweenCore-1andAccess-2uses interfacege-0/0/16.0on the Core-1 side.

Output Analysis:However, the show protocols mvrp output for Core-1 only lists interfaces ge-0/0/14.0 and ge-0/0/15.0.

MVRP Requirements:For MVRP to successfully propagate VLAN information between Access-2 and the rest of the network, the protocol must be enabled on every trunk interface in the path.

Solution:Becausege-0/0/16.0is missing from the Core-1 MVRP configuration, VLAN registration messages from Access-2 are not being processed by Core-1. Configuring this interface under MVRP on Core-1 will solve the communication problem.

The exhibit shows router1 (AS 65001) connected to router2 (AS 65002) via two parallel physical links. The show bgp summary output indicates that sessions are established with two neighbors: 10.10.10.1 and 10.10.20.1. Currently, for the second neighbor (10.10.20.1), there are0 active routesdespite having4 accepted routes, which indicates that BGP has selected only one "best path" via the first neighbor for forwarding.

BGP Best Path Selection:By default, BGP only selects a single best path for any given destination prefix and installs that one path into the forwarding table. In a topology with parallel links to the same AS, this leads to underutilization of available bandwidth.

Multipath Solution (Option B):To enableactive routesfrom both peers and allow for load-balancing (ECMP) across both links, you must enable themultipathfeature.

When the multipath statement is configured under the protocols bgp group ext-peers hierarchy, it tells Junos OS to install multiple equal-cost BGP paths into the routing table and subsequent forwarding table.

Since both neighbors belong to the same peer group (ext-peers) and the same AS (65002), configuring multipath at the group level will apply to both sessions, allowing paths from both neighbors to be marked as "active".

Incorrect Options:

Option A:172.16.1.1 is the loopback address of router2. The exhibit shows peering is currently done using physical interface addresses (10.10.10.1 and 10.10.20.1), so this address is irrelevant to the current active sessions.

Option C:Configuring the neighbor address alone without the multipath parameter will not change the best-path selection behavior.

Option D:10.10.20.2 is the local interface IP of router1, not the neighbor's IP. BGP multipath must be configured to point to remote peer paths.

Configuration Example for Junos OS 24.4:To implement this, apply the following command: set protocols bgp group ext-peers multipath

To secure a Layer 2 network runningMultiple VLAN Registration Protocol (MVRP)against unauthorized VLAN propagation from rogue devices, you must control the registration state of the ports.

Forbidden Registration Mode (Option D):This mode is specifically designed to prevent an interface from participating in the MVRP exchange.

When a port is set to forbidden, it willneither register nor declare VLANs(except those statically configured on the interface).

If a rogue device sends MVRP PDUs to this interface, the distribution switch willignore those PDUs, preventing the rogue device from dynamically creating or learning VLANs through that port.

Registration Hierarchy:In Junos OS 24.4, this is configured at the [edit protocols mvrp interface registration forbidden] level.

Other Modes:normal (default) allows full participation, while restricted ignores joins for VLANs not already statically defined on the switch but still declares its own.

In Junos OS Class of Service (CoS) processing, there is a specific order of operation for packet classification.

Precedence of Multifield (MF) Classifiers:When both a Behavior Aggregate (BA) classifier and a Multifield (MF) classifier are applied to an interface, theMF classifier takes precedence.

Processing Order:

The BA classifier (e.g., DSCP or 802.1p) inspects the packet header and assigns an initial forwarding class and loss priority.

The MF classifier (which looks at multiple fields like source/destination IP and port) is processed later in the pipeline.

The "Final Word":Because the MF classifier is evaluated later, its resultsoverwriteany previous assignments made by the BA classifier. Therefore, if a packet matches both, the MF classifier determines the final forwarding class assignment.