Practice Free JN0-650 Enterprise Routing and Switching - Professional (JNCIP-ENT) Exam Questions Answers With Explanation

Private VLANs (PVLANs) provide Layer 2 isolation between ports within the same broadcast domain. When a PVLAN spans multiple switches, a special type of trunk configuration is required to maintain the isolation and community logic across the inter-switch links.

Isolated VLAN Trunking (Option D): To extend an isolated VLAN across multiple switches, you must configure the trunk port on each switch to allow the isolated VLAN ID. In Junos OS, this is specifically achieved by configuring the interface as a trunk and associating it with the primary VLAN and the specific isolated VLAN. The correct syntax for enabling this inter-switch communication is to configure trunk ports that recognize the isolated VLAN tag (e.g., set interfaces < interface > unit 0 family ethernet-switching vlan members [ primary-vlan isolated-vlan ]).

Forwarding Rules: Traffic from an isolated port on Switch A must reach a promiscuous port (often on Switch B) to exit the PVLAN. The inter-switch trunk carries this traffic using the secondary (isolated) VLAN ID, ensuring that it remains isolated from other host ports on the remote switch.

Option A (inter-switch-link): In standard Junos switching, the inter-switch-link statement is used in Virtual Chassis or specific fabric designs, but for standard PVLAN extension, standard 802.1Q trunking with secondary VLAN IDs is the mechanism used.

Options B and C: These describe specific port roles (isolated vs. community) rather than the method used to enable trunking between switches.

To simplify VLAN management and automate the creation and pruning of VLANs across a network, Juniper utilizes the Multiple VLAN Registration Protocol (MVRP).

MVRP on Trunk Interfaces (Option C): MVRP is the IEEE 802.1ak standard that replaces the older, proprietary GVRP. It is designed to run on trunk interfaces between switches.

Dynamic Creation: When a VLAN is added to one switch, MVRP advertises its existence to neighboring switches. If those switches need to reach that VLAN, they can dynamically create it in their database.

Pruning: If a switch no longer has any active ports or downstream neighbors interested in a specific VLAN, it stops advertising that VLAN on its trunks. This " prunes " the VLAN traffic from those links, saving bandwidth.

Incorrect Options: Option A and B are incorrect because GVRP is legacy and no longer the recommended protocol for modern Junos deployments. Option D is incorrect because MVRP is meant for inter-switch trunk links to manage the fabric, not for edge access ports where VLAN membership is usually static.

Junos OS 24.4 on EX Series switches provides robust support for LLDP (Link Layer Discovery Protocol) and its extension, LLDP-MED (Media Endpoint Discovery).

LLDP-MED Power Negotiation: This feature allows a switch (Power Sourcing Equipment or PSE) and a connected device (Powered Device or PD), such as an IP phone or access point, to negotiate power requirements beyond the standard IEEE 802.3af/at classes. The switch can dynamically allocate the exact amount of power the device needs (in 0.1W increments), which optimizes the power budget of the switch.

LLDP Scope: LLDP is a Link Layer protocol (Layer 2), but it is not restricted to Layer 2 interfaces; it can also operate on Layer 3 interfaces to advertise system identity and capabilities. This makes Option A incorrect.

Link-Local Protocol: LLDP frames use a specific multicast MAC address (01:80:c2:00:00:0e) that is not flooded or forwarded by switches. They are strictly link-local between two directly connected neighbors. This makes Option B incorrect.

Endpoint Focus: LLDP-MED is specifically designed for Media Endpoint Devices (like VoIP phones), providing TLVs for network policy (VLAN/QoS), location identification, and inventory management. Standard LLDP is used for discovering network connectivity devices. This makes Option D incorrect.

The exhibit shows a BGP routing process where an Import Policy is being applied to routes received in the RIB-IN. Specifically, Policy 1 states: " Reject 0.0.0.0/0 from AS 64512. "

In Junos OS, when a routing policy rejects a route, that route is not placed in the main routing table (inet.0) for active use. Instead, it becomes a hidden route. To verify that a specific peer is actually sending a route that is subsequently being rejected by your policy, you must use specific diagnostic commands:

Understanding " Hidden " Routes: When a BGP route is received but fails to meet policy requirements (or has an unreachable next-hop), Junos keeps it in the BGP RIB-IN but marks it as " hidden. " It will not appear in a standard show route command.

Command Logic (Option D): The command show route receive-protocol bgp < peer ip > hidden allows an administrator to view all routes received from a specific neighbor, including those that were rejected by import policies.

show route receive-protocol bgp < peer ip > : Shows only the routes that passed the import policy and were accepted into the table. Since the 0.0.0.0/0 route from AS 64512 is explicitly rejected in the exhibit, it would not show up here.

Adding the hidden keyword is the essential step to see the rejected default route and verify that AS 64512 is indeed sending it before the policy drops it.

Other Options:

Option A is incorrect because it only shows accepted routes.

Option B and C are used to filter the existing active routing table based on gateway or next-hop attributes, but they cannot show routes that have been rejected and excluded from that table.

In an EVPN-VXLAN architecture, the network is divided into two distinct planes: the Underlay and the Overlay.

Underlay (IP Fabric): The underlay ' s only job is to provide IP reachability between the loopback addresses of all VTEPs (Virtual Tunnel Endpoints). This is typically achieved using OSPF, IS-IS, or EBGP.

Overlay (EVPN Control Plane): The overlay is responsible for carrying Layer 2 MAC and Layer 3 IP reachability information between switches. EVPN signaling is the standard mechanism for this task.

Protocol Choice (Option D): EVPN uses MP-BGP (Multiprotocol BGP) as its control plane protocol. On Juniper EX Series and QFX Series switches, the most scalable and recommended design for the overlay is EBGP (External BGP).

In a 3-stage or 5-stage Clos architecture, EBGP is used in the overlay to exchange EVPN routes (Route Types 1-5) between Leaf and Spine switches.

EBGP simplifies configuration by avoiding the need for Route Reflectors (required for IBGP) and provides better control over route propagation through BGP community and policy management.

Incorrect Options:

Options A and B refer to the underlay protocols. While they provide the path for the VXLAN tunnels, they do not handle the EVPN signaling itself.

Option C (MPLS) is a different transport technology. While EVPN can run over MPLS (EVPN-MPLS), campus designs on EX series devices specifically use VXLAN as the data plane, making EBGP the standard signaling protocol for the EVPN-VXLAN overlay.

This scenario describes the standard transition of Class of Service (CoS) metadata from the network edge to the network core.

MF vs. BA Classification: Edge devices use Multifield (MF) classifiers because incoming traffic often lacks markings. MF classification assigns traffic to an internal forwarding class based on multiple fields (IPs, ports, etc.). Core devices use Behavior Aggregate (BA) classifiers because they are faster; they only look at the CoS bits (like DSCP) in the header to determine the forwarding class.

The Problem: Internal forwarding class assignments made by an MF classifier on the edge device do not automatically travel with the packet. If the packet leaves the edge device with its original (potentially zeroed) DSCP bits, the core device ' s BA classifier will not be able to identify the priority.

The Solution (Option A): You must implement rewrite rules on the egress interfaces of the edge devices. A rewrite rule takes the internal forwarding class and loss priority assigned by the MF classifier and " writes " the corresponding DSCP value into the packet header as it exits toward the core. This ensures that the core device sees the correct DSCP marking and can apply the appropriate BA classification.

Incorrect Options: Rewrite rules are strictly an egress function to modify the packet for the next hop. Applying them on ingress (Option B) or core ingress (Option C) does not solve the problem of ensuring the packet header reflects the classification logic used during the internal switching process of the edge device.

The show ospf interface output provides critical information about the local OSPF state.

Loopback Behavior (Option A): The output shows lo0.0 is in the DR (Designated Router) state with Nbrs 0. In Junos OS, OSPF adjacencies are not formed over loopback interfaces; they are treated as stub networks.

Neighbor State (Option D): Every interface listed (ge-0/0/1.0, ge-0/0/2.0, and lo0.0) shows Nbrs 0. This indicates that the router is not seeing any OSPF neighbors. Since the physical interfaces are in the DR state (meaning the router has elected itself as the DR because no other routers responded), it confirms the router is not receiving OSPF Hello messages from any potential neighbors on those segments.

Router ID: The DR ID 192.168.1.17 is the local router ' s own ID, not a neighbor it is trying to reach.

The exhibit shows the Class of Service (CoS) transmit queue information for interface ge-0/0/11. To determine the correct behavior, we must analyze the bandwidth allocations and the queue limit settings:

Bandwidth Calculation (Option A): In Junos OS, when multiple queues are assigned specific percentages of bandwidth, the " remainder " (represented by ' r ' ) is the total interface bandwidth minus the sum of the explicitly configured percentages.

Bandwidth assigned to Queue 1 (EF) = 10%.

Bandwidth assigned to Queue 2 (AF) = 10%.

Bandwidth assigned to Queue 3 (NC) = 4%.

Total explicitly assigned = $10\% + 10\% + 4\% = 24\%$.

Remainder for Queue 0 (Best Effort) = $100\% - 24\% = 76\%$.

" Limit: exact " Behavior (Option B): The exhibit shows that Queue 2 (assured-forwarding) has a Limit set to exact.

By default, a queue in Junos can consume more than its allocated bandwidth if other queues are idle.

However, when the exact keyword is applied to the transmit-rate (transmission rate), the queue is strictly rate-limited to its configured percentage.

This means that traffic in Queue 2 will be capped at 10% of the interface bandwidth regardless of whether the network is congested or not. If the traffic exceeds 10%, the excess will be dropped or buffered to match the exact rate.

Option C is incorrect because 100% of the bandwidth is not reserved for a single queue; it is distributed across four queues.

Option D is less accurate than B because it implies the drop behavior only occurs during congestion. The exact parameter enforces the limit even when the rest of the interface is completely idle.

In Junos OS, particularly in BGP-based environments like EVPN-VXLAN or MPLS, the router often needs to perform a recursive lookup to resolve the BGP next-hop of a route.

Next-Hop Resolution (Option C): When an EVPN route (found in default-switch.evpn.0) is received, the protocol next-hop is typically the loopback IP of the remote VTEP. To actually forward traffic, the switch must know how to reach that loopback IP.

The inet.3 table is the default table in Junos used to store egress interface information for BGP next-hops.

While inet.0 handles standard unicast routing, inet.3 is specifically consulted for resolving the path toward BGP peers. In an EVPN context, this ensures that the VXLAN tunnel endpoint is reachable and properly resolved through the underlay.

Other Tables: * inet.2 (Option A) is used for Multicast RPF checks.

default-switch.evpn.0 (Option B) stores the EVPN routes themselves (MAC/IP), but it is the source of the lookup, not the table where the recursive resolution occurs.

vxlan.inet (Option D) is an internal table used to track active VXLAN tunnels but is not the primary table for recursive BGP next-hop validation.

The exhibit shows a BGP Route Reflector (RR) configuration where an export policy named NHS (Next-Hop Self) is applied to the internal BGP group int-group. The policy NHS sets the next-hop self attribute for BGP routes.

The Problem (Traffic Tromboning): In a standard BGP Route Reflector design, the RR should reflect routes without modifying the BGP next-hop attribute. By applying a next-hop self policy on the export to clients, the RR tells all its clients that it is the exit point for those routes. Consequently, all data plane traffic is sent to the RR first before being forwarded to the actual destination, rather than following the optimal direct path between clients. This is known as " traffic tromboning " or suboptimal routing.

The Solution (Option C): The most direct way to fix this is to delete the export policy that is forcing the next-hop to be the RR. By deleting protocols bgp group int-group export NHS, the RR will resume standard behavior and reflect the original next-hop received from the route source, allowing clients to route traffic directly to the correct destination.

The Refined Solution (Option D): If you must keep the NHS policy (perhaps for routes learned from external peers), you should ensure it only applies to those specific routes. By adding from route-type internal to the policy term and then potentially changing the logic (or simply narrowing the scope), you can prevent the RR from incorrectly applying next-hop self to internal routes that it is merely reflecting. In the context of this specific problem, Option D combined with a change in the policy ' s action or scope helps ensure reflected internal routes maintain their original, optimal next-hops.

Option A is incorrect because setting next-hop self for external routes is common practice, but it doesn ' t solve the problem of internal reflected routes being diverted to the RR.

Option B is incorrect because applying this as an import policy would change how the RR itself sees the routes, but it wouldn ' t fix the attributes being sent out to the clients in the reflection process.

In Junos OS Class of Service (CoS), a scheduler is the mechanism used to assign resources to the various egress queues on an interface. Specifically, when utilizing a modified deficit round-robin (MDRR) or weighted round-robin algorithm to service these queues, the scheduler ' s behavior is defined by two primary variables:

Transmit Rate (Option A): This variable defines the minimum guaranteed bandwidth for a queue. In the context of a deficit round-robin algorithm, the transmit rate serves as the weight for the queue. Queues with higher transmit rates receive a larger " quantum " of data they can send during each round-robin cycle compared to queues with lower rates.

Buffer Size (Option C): This variable defines the amount of memory (buffer space) allocated to the queue. It ensures that the queue can hold a certain amount of delayed traffic during periods of congestion to prevent immediate packet drops. The buffer size can be configured as a percentage of the total interface buffer or as a temporal value.

Why other options are incorrect:

Layer 2 and Layer 3 fields (Options B & D): These fields are utilized by classifiers (Behavior Aggregate or Multifield) to identify and group traffic into forwarding classes. They are used before the scheduling process begins and do not define the resource allocation of the scheduler itself.

When integrating a QFX Series switch into an EVPN-VXLAN IP fabric, specific BGP and EVPN hierarchy configurations are required to establish the control and data planes:

EVPN Encapsulation (Option A): In Junos OS, the encapsulation vxlan statement must be explicitly configured under the protocols evpn hierarchy. This defines that the EVPN control plane will use VXLAN as the data plane encapsulation method rather than MPLS.

BGP Address Family (Option C): EVPN uses Multiprotocol BGP (MP-BGP) to distribute reachability information. For the control plane to function, you must enable the EVPN signaling address family under the BGP protocol using the command set protocols bgp group < name > family evpn signaling.

Incorrect Options: Option B is incorrect because family vpls is used for traditional VPLS signaled by BGP, not for EVPN-VXLAN. Option D is incorrect because while the loopback interface must be reachable, it is typically advertised via an IGP (like OSPF or IS-IS) to provide the underlay connectivity that BGP then rides upon; BGP itself does not " advertise " the loopback to establish the initial peerings.

This scenario describes a specific use case where a switch port is shared by multiple devices (e.g., via a downstream unmanaged switch), and you want to simplify the authentication process.

Single Supplicant Mode (Option A): In this mode, the switch requires only the first device that connects to the port to successfully authenticate via 802.1X. Once that first device is authorized, the switch " opens " the port for all traffic. This means all subsequent devices attached to that same downstream switch are permitted to access the network without undergoing their own authentication.

Other Modes:

Single-secure supplicant (C): Only allows the first authenticated device; all others are blocked.

Multiple supplicant (D): Requires every device to authenticate individually.

MAC RADIUS (B): This is an authentication method, not a port-control mode.

This question focuses on port security and preventing " rogue switches " or multiple devices from accessing a single physical port simultaneously.

Single-Secure Supplicant Mode (Option A): This is the most restrictive 802.1X mode in Junos OS. It allows exactly one MAC address to be authenticated on the port at a time. If a device successfully authenticates, the switch will drop any traffic coming from any other MAC address on that same physical interface. If a user tries to plug in a switch, only the first device that authenticates will have access; all other devices behind that switch will be blocked.

Single Supplicant Mode (Option C): This mode allows the first authenticated user to " open " the port for all other users. This would actually allow a rogue switch to function once the first device is authorized.

Multiple Supplicant Mode (Option B): This allows multiple devices to connect, provided each one authenticates individually. While secure, it does not prevent a user from connecting multiple devices to the port, which violates the requirement to allow only one.

MAC-RADIUS (Option D): This is an authentication method, not a port-access mode that limits the number of supplicants.

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.

The exhibit illustrates an Autonomous System (AS 65512) receiving the same prefix ($203.0.113.0/24$) from two different neighbors, ISP A and ISP B. To influence outbound traffic from AS 65512 so that ISP A is preferred, you must manipulate the BGP Local Preference attribute.BGP Path Selection and Local Preference: Local preference is the first attribute evaluated by BGP after checking if the next hop is reachable. A higher local preference value is always preferred over a lower one. The default value in Junos OS is 100.Applying the Preference (Option B): By applying an import policy on router R1 to set a local preference higher than 100 (e.g., 200) for routes from ISP A, R1, R2, and R3 will all prefer the path through R1 to reach ISP A.Applying the Preference (Option C): Alternatively, you can achieve the same result by applying an import policy on R2 to set a local preference lower than 100 (e.g., 50) for routes from ISP B. Since the routes from R1 remain at the default of 100, the path through ISP A (100) will be preferred over ISP B (50).Why A and D are incorrect: Setting a lower preference for ISP A (Option A) or a higher preference for ISP B (Option D) would result in ISP B being preferred for outbound traffic, which is the opposite of the requirement.