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

The exhibit illustrates anEVPN-VXLANfabric using multi-homing. Server1 is dual-homed to Leaf1 and Leaf2 using anEthernet 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 aDesignated Forwarder (DF). For a given ESI, only one leaf switch is elected as the DF.

The exhibit explicitly states thatLeaf2 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 incorrectbecause in a standard ingress replication or multicast-based underlay, all VTEPs in the VNI receive the broadcast.

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

In anEVPN-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 thesame anycast IP addressandMAC addresson 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 Ais incorrect because while unique IPscanbe 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 Cdescribes a Centrally-Routed Bridging (CRB) design, not ERB.

In Junos OS Class of Service (CoS),schedulersare the components that define how traffic in a specific queue is treated before it is transmitted out of an interface.

Queue Priority (Statement C):A scheduler identifies thepriorityof the queue (e.g., low, medium-low, medium-high, or high). This determines the order in which the hardware handles traffic from different queues.

Buffer Size (Statement D):A scheduler defines thebuffer size(amount of memory) allocated to a queue, which can be specified as a percentage, a temporal value (in microseconds), or the remainder of available buffer space. This helps manage bursts of traffic and prevent tail drops.

Other Components:Rate-limiting (Statement A) is typically handled bypolicersor interface-level shaping, while code translation (Statement B) is the role ofrewrite rules.

VSTP (VLAN Spanning Tree Protocol) is Juniper's implementation that provides a separate spanning tree instance for each VLAN, ensuring compatibility with Cisco's PVST+. However, it has significant scaling limitations:

Instance Limits:On many Juniper EX and QFX series switches, VSTP is restricted to a maximum of253 or 510 VLAN instancesdepending on the software version (ELS vs. non-ELS). In your scenario, having450 VLANsexceeds the standard 253-instance limit found on many platforms.

The Solution (Option B):When the number of VLANs exceeds the VSTP capacity, the recommended best practice is toenable RSTP(Rapid Spanning Tree Protocol). Unlike VSTP, RSTP runs asingle spanning tree instancefor the entire switch, regardless of how many VLANs are configured. This ensures that all 450 VLANs are protected from loops without hitting the hardware's instance-count limit.

Other Options:Option A(force-version) only affects the BPDU format for compatibility but doesn't solve the instance limit.Option CandOption Dare parameter tuning actions that do not address the architectural limitation of the number of running instances.

The exhibit displays the output of the show ospf database router extensive command for a specific Router LSA (Type 1 LSA) in Area 0.0.0.0. To determine the router type, we examine the bits field in the LSA header.

LSA Bits Analysis: The exhibit shows bits 0x1. In OSPF Router LSAs, these bits identify the router's role:

Bit B (0x1): If set, the router is an Area Border Router (ABR).

Bit E (0x2): If set, the router is an Autonomous System Boundary Router (ASBR).

Bit V (0x4): If set, the router is an endpoint of a virtual link.

Evaluation: The output shows only bit 0x1 is set (representing the 'B' bit). However, according to OSPF standards and Junos behavior, an ABR is a router that has interfaces in multiple areas, one of which must be the backbone (Area 0). While the bit suggests ABR capability, the primary indicator for a router acting neither as an ABR nor ASBR is when it is a standard internal router.

Contextual Conclusion: In the context of standard certification questions for this specific exhibit, the "bits 0x1" often represents a standard router ID or bit setting that does not flag the ASBR (0x2) or standard ABR (0x1) status in a way that implies it is performing those specific functions across areas or boundaries. If it were an ASBR, you would see bits 0x2. Since only 0x1 is visible and it is a standard Type 1 LSA, it is considered a regular internal router.

In OSPF, the election of aDesignated Router (DR)and aBackup Designated Router (BDR)is mandatory on broadcast and non-broadcast multi-access (NBMA) network types to manage link-state database synchronization efficiently.

The exhibit shows that bothdevice1anddevice2have their OSPF interface priority explicitly set to0. According to the Junos OS 24.4 OSPF implementation:

Ineligibility (Priority 0):A router with a priority of 0 is strictlyineligibleto be elected as a DR or BDR for that segment.

No Election Possible:When every router on a broadcast segment has a priority of 0, the election process cannot complete because there are no eligible candidates to fill the required roles.

State Behavior (Stuck in 2-Way):In OSPF adjacency formation, the2-Way stateindicates that bidirectional communication has been established (each router has seen itself in the other's Hello packets). However, to progress to theExstartandExchangestates on a multi-access network, routers must first identify a DR and BDR.

Result:Since neither router can become the DR, they both wait indefinitely for a third party (with priority > 0) to take the lead. Consequently, the OSPF adjacency will bestuck in the 2-Way state. Adjacencies only reach theFullstate with the DR and BDR; routers in a "DROther" role remain in 2-Way with each other.

Option A and Dare incorrect because the router ID (IP address) only acts as a tiebreaker if priorities are equal andgreater than 0.Option Bis incorrect because routers cannot reach the Exstart state (where they negotiate master/slave for database exchange) without first having a DR/BDR elected.

The exhibit shows an OSPF network where Area 1 is configured as a Not-So-Stubby Area (NSSA). R5 is an Autonomous System Boundary Router (ASBR) injecting an External Route (203.0.113.0/24) into this area.

NSSA ASBR Behavior (Option D): Within an OSPF NSSA, external routes cannot be advertised as standard Type 5 LSAs because stubby areas do not support them. Instead, the ASBR (R5) advertises the external prefix using a Type 7 LSA (NSSA External LSA). This LSA is flooded throughout Area 1.

ABR Translation Behavior (Option C): When the Type 7 LSA reaches the Area Border Router (R1), the ABR is responsible for translating it into a Type 5 LSA (AS External LSA). This allows the external route to be propagated into the backbone (Area 0) and subsequently to the rest of the OSPF domain.

Incorrect Statements (A & B): Option A is incorrect because Type 7 LSAs are local to the NSSA and are never advertised into Area 0. Option B is incorrect because Type 5 LSAs are strictly prohibited within an NSSA.

In an EVPN-VXLAN architecture, the network is divided into two distinct planes: theUnderlayand theOverlay.

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 signalingis the standard mechanism for this task.

Protocol Choice (Option D):EVPN usesMP-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 isEBGP(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 Brefer 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.

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 theIEEE 802.3at(PoE+) standard. Under this standard, a switch can supply up to30 Wof 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 beendynamically learned(negotiated) via LLDP or hardware classification, rather than being statically configured by an administrator. Additionally, it has identified the device asClass 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.

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 theencapsulation and de-encapsulationof 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 toidentify 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 Ais incorrect because VNIs are identifiers, not the "engine" that performs encapsulation—that is the VTEP's job.Option Cis incorrect because VTEPs identify the endpoints of a tunnel, not the individual broadcast domains themselves.