JN0-650 Enterprise Routing and Switching - Professional (JNCIP-ENT) Questions and Answers

In an EVPN-VXLAN architecture, the interaction between the control plane (EVPN) and the data plane (VXLAN) is defined by specific functional components:

VTEP (VXLAN Tunnel End Point): These are the entities responsible for the encapsulation and de-encapsulation of Layer 2 Ethernet frames into Layer 3 UDP/IP packets. A VTEP can be a physical switch (like a QFX or EX series) or a software-based entity. When traffic enters the fabric, the ingress VTEP wraps it in a VXLAN header; the egress VTEP removes this header before delivering it to the destination host. (Option B)

VNI (Virtual Network Identifier): The VNI is a 24-bit field in the VXLAN header that allows for up to 16 million unique identifiers. It is used to identify specific broadcast domains (or VLANs) within the overlay network. Each VNI effectively represents a virtualized Layer 2 segment that is stretched across the Layer 3 underlay. (Option D)

Incorrect statements: Option A is incorrect because VNIs are identifiers, not the "engine" that performs encapsulation—that is the VTEP's job. Option C is incorrect because VTEPs identify the endpoints of a tunnel, not the individual broadcast domains themselves.

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.

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.

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.

The exhibit shows the output of the show poe interface command on a Juniper switch.

VTEP Power Capabilities (Statement D): The exhibit shows the Pair/Mode as 2P/AT, which refers to the IEEE 802.3at (PoE+) standard. Under this standard, a switch can supply up to 30 W of power per port to attached devices (PDs). * Dynamic Learning (Statement C): Looking at the Max power column for port ge-0/0/0, it shows 19.5W(L). The (L) indicator signifies that the power has been dynamically learned (negotiated) via LLDP or hardware classification, rather than being statically configured by an administrator. Additionally, it has identified the device as Class 4, which is a standard dynamic classification for PoE+ devices.

Why others are incorrect: Statement A (60 W) refers to the 802.3bt (PoE++) standard, which is not indicated here. Statement B is incorrect because the "(L)" confirms the configuration is not static.

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 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 : 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 PIM Sparse Mode (PIM-SM), the Rendezvous Point (RP) is the cornerstone of the multicast distribution model.

The Meeting Point (Option A): The RP serves as a central clearinghouse where multicast sources and receivers meet.

When a source starts transmitting, the first-hop router encapsulates the data and sends it to the RP via a PIM Register message.

When a receiver wants to join a group, its last-hop router sends a (*,G) PIM Join request toward the RP.

The RP then manages the distribution from the source to the receivers until a Shortest Path Tree (SPT) can be established directly between them.

Incorrect Statements: Option B is incorrect because PIM Dense Mode does not use an RP; it uses a "flood and prune" mechanism. Option C is incorrect because the RP only forwards traffic to interfaces that have explicitly requested it via Join messages, which is what makes it "sparse". Option D is incorrect because SSM (Source-Specific Multicast) specifically avoids using an RP by having receivers join a known source directly.

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.

To secure a Layer 2 network running Multiple 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 will neither register nor declare VLANs (except those statically configured on the interface).

If a rogue device sends MVRP PDUs to this interface, the distribution switch will ignore 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.

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 Junos OS routing policies, the order of evaluation and the impact of terminal actions are critical for predictable control.

Immediate Execution (Option D): When a route-filter contains an explicit action like accept or reject within its block, that action is considered terminal if a match is found.

Evaluation Flow: The policy engine processes terms and conditions from top to bottom. If a prefix matches a route-filter that has an embedded accept action, the policy executes that action immediately and stops further evaluation of that specific term. Consequently, any subsequent then clause in the same term is completely ignored.

Best Practice: To ensure a then clause (which might include modifications like changing a preference or community) is executed, the route-filter should be defined without an internal action, allowing the match to fall through to the term's common then statement.

The exhibit shows a custom Behavior Aggregate (BA) classifier named my-classifier for the Differentiated Services Code Point (DSCP) protocol.

Importing Defaults (Statement C): The configuration line import default; is crucial. In Junos OS, when you create a custom classifier, you can use this statement to import the default mapping table for all code points that you have not explicitly defined in the current block. This ensures that only the specific traffic types you care about are customized while the rest follows industry-standard defaults.

Logical Interface Association (Statement A): In the Junos class-of-service hierarchy, classifiers are typically applied to logical interfaces (e.g., ge-0/0/0.0). While they can sometimes be applied at a higher level, the standard practice for enterprise routing and switching is to associate them with the logical unit to provide granular control over subinterfaces or VLAN-tagged traffic.

Why others are incorrect: Statement B is less accurate because the primary binding point in Junos is the unit (logical interface). Statement D is incorrect because the specific classifications defined in the custom block override the defaults; they are not overwritten by them.

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

OSPF Overload (Option B): When you enable overload under protocols ospf, the router advertises its own Link-State Advertisements (LSAs) with a maximum 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, effectively moving transit traffic off the router while still allowing management traffic directed to the 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.

The exhibit illustrates an EVPN-VXLAN fabric using multi-homing. Server1 is dual-homed to Leaf1 and Leaf2 using an Ethernet Segment Identifier (ESI) in an active-active or active-standby configuration. Server2 is single-homed to Leaf3.

In EVPN environments, specific mechanisms are used to prevent loops and duplicate traffic when dealing with Broadcast, Unknown Unicast, and Multicast (BUM) traffic:

Broadcast Propagation (Option A): When Server2 (connected to Leaf3) generates a broadcast frame, Leaf3 encapsulates this traffic into a VXLAN tunnel and forwards it to all other VTEPs (Virtual Tunnel End Points) that participate in that specific Virtual Network Instance (VNI). Therefore, both Leaf1 and Leaf2 will receive the broadcast frame from the core fabric.

Designated Forwarder (DF) Election (Option C): To prevent a multi-homed device (like Server1) from receiving duplicate copies of the same broadcast frame from multiple leaf switches, EVPN utilizes a Designated Forwarder (DF). For a given ESI, only one leaf switch is elected as the DF.

The exhibit explicitly states that Leaf2 is the Designated Forwarder.

According to the Junos EVPN implementation, only the DF is responsible for decapsulating BUM traffic received from the core and forwarding it to the local access segment.

While Leaf1 receives the frame (Option A), it will see that it is not the DF for that segment and will drop the frame rather than forwarding it to Server1. This ensures Server1 receives exactly one copy of the broadcast, delivered by Leaf2.

Option B is incorrect because in a standard ingress replication or multicast-based underlay, all VTEPs in the VNI receive the broadcast.

Option D is incorrect because Leaf1 is the non-designated forwarder (non-DF) for this segment and is prohibited from forwarding BUM traffic to the ESI.

When 802.1X server fail fallback is enabled with the vlan-name feature, the switch provides a specific survival mechanism for both existing and new sessions when the RADIUS server becomes unreachable.

Existing Clients (Statement B): Clients that have already successfully authenticated are unaffected by the server's unavailability in the short term. They maintain their current network access until their specific re-authentication timer expires. Only then will the switch attempt to contact the server again and trigger the fallback action if the server remains down.

New Clients (Statement D): For any new device attempting to connect while the RADIUS server is down, the switch cannot perform a standard authentication. Under the vlan-name fallback configuration, these new clients are automatically placed into the specified fallback VLAN and granted access based on the local policy defined for that VLAN.

Why others are incorrect: Statement A is incorrect because disconnecting active users would cause unnecessary service disruption. Statement C is incorrect because new clients cannot "request" a VLAN during the 802.1X handshake; the switch assigns it based on the fallback configuration.

In an EVPN-VXLAN Edge-Routed Bridging (ERB) architecture, also known as a collapsed fabric, the Layer 3 default gateway functionality is moved from the core/spine layer down to the edge (the leaf or distribution layer).

Anycast Gateways: To support seamless host mobility and redundancy, multiple distribution/leaf switches are configured with the same anycast IP address and MAC address on their IRB interfaces for a given VLAN. This allows a host to move between different switches without needing to update its default gateway configuration or ARP cache.

Distributed Routing: Routing occurs locally at the edge (distribution layer). Traffic destined for a different subnet is routed by the first switch it hits (the ingress leaf), rather than being backhauled to a central core router.

Symmetric vs. Asymmetric IRB: Junos OS 24.4 supports both models, but the ERB design typically utilizes symmetric routing for better scalability, where each leaf only needs to know the routes for its locally connected VNIs and uses a transit VNI for inter-subnet communication.

Option A is incorrect because while unique IPs can be used (Method 1 in some docs), the defining characteristic of an efficient ERB design is the use of shared Anycast IPs for the gateway. Option C describes a Centrally-Routed Bridging (CRB) design, not ERB.