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

VSTP (VLAN Spanning Tree Protocol) is designed for interoperability with environments running Cisco’s Per-VLAN Spanning Tree Plus (PVST+).

Per-VLAN Instances (Option E):The core function of VSTP is to maintain aseparate spanning tree instancefor every VLAN configured on the switch. This allows for different root bridges and different topologies per VLAN, enabling traffic load-balancing across various physical links.

BPDU Generation (Option A):Because each VLAN has its own instance, VSTP must sendseparate BPDUsfor each VLAN. These BPDUs are tagged with the respective VLAN ID to ensure the receiving switch can process them for the correct instance.

Instance Limits (Option D):On many Juniper platforms, VSTP is limited to supporting a maximum of253 unique spanning tree topologies(instances). If the number of VLANs exceeds this limit, additional VLANs will not have spanning tree protection unless migrated to a different protocol like MSTP.

Incorrect Statements:Option Bis incorrect because VSTP is compatible with RSTP; it actually uses RSTP algorithms (Rapid-VSTP) by default in modern Junos versions to provide fast convergence.Option Cis incorrect because STP or RSTP is usually the default spanning tree protocol on EX Series switches, not VSTP.

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.

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 thefirst devicethat 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 meansall subsequent devicesattached 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):Requireseverydevice to authenticate individually.

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

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 family evpn signaling.

Incorrect Options:Option Bis incorrect because family vpls is used for traditional VPLS signaled by BGP, not for EVPN-VXLAN.Option Dis incorrect because while the loopback interface must be reachable, it is typically advertised via anIGP(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.

In Junos OS 24.4, Captive Portal is used as a web-based authentication method for Layer 2 network access control, often in environments where 802.1X is not feasible for all users.

Fallback Mechanism (Option D):On EX Series switches, Juniper supports aflexible authentication order. By default, the switch attempts authentication in the order of802.1X, thenMAC RADIUS, and finallyCaptive Portal. If a client fails both 802.1X and MAC RADIUS, the switch can fall back to Captive Portal to redirect the user to a login page.

MAC Allowlist (Option B):Captive Portal relies on intercepting HTTP/HTTPS traffic to redirect users. However, "headless" devices like printers or cameras lack web browsers and cannot interact with the portal. To accommodate these, Junos allows administrators to configure anauthentication allowlist(or whitelist), which identifies these devices by their MAC addresses and permits them to bypass the portal entirely.

Precedence (Option A):This is incorrect because Captive Portal is generally thelastmethod in the default sequence, not the first.

Layer 2 Participation (Option C):While Captive Portal requires a Layer 3 interface (RVI/IRB) for the redirection process, it is explicitly used to controlLayer 2 accesson EX Series switches.

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.

The exhibit shows the MSTP configuration for two switches,switch1andswitch2. MSTP allows you to group multiple VLANs into a single Multiple Spanning Tree Instance (MSTI), enabling different root bridges and topologies for different sets of VLANs.

Root Bridge Election (Option B):For any Spanning Tree instance, the switch with thelowest bridge priorityis elected as the root bridge.

Formsti 2, switch1 has a priority of4k(4096), while switch2 has a priority of8k(8192).

Since 4096 < 8192,switch1 is elected the root bridge for msti 2.

Failover Behavior (Option D):Spanning Tree is designed for redundancy. If a primary root bridge fails, the remaining switches in the network re-elect a new root based on the next lowest priority.

Ifswitch2goes down, switch1 becomes the only switch in the region.

Regardless of its original priority (4k or 8k), switch1 will take over as theroot bridge for both msti 1 and msti 2because there are no other contenders with a better (lower) priority.

Incorrect Statements:Option Ais incorrect because for msti 1, switch2 has the lower priority (4k vs. 8k), making switch2 the root bridge.Option Cis incorrect because it contradicts the fundamental high-availability nature of Spanning Tree.

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.

EVPN Route Type 5 (IP Prefix Route) is used to advertise IP prefixes (subnets) between broadcast domains or between VRFs in an EVPN fabric.

IP-VRF-to-IP-VRF (Statement C):In an EVPN-VXLAN architecture, Type 5 routes are primarily used forLayer 3 connectivity. They allow different IP-VRFs on different VTEPs to exchange prefix information directly. This model is widely referred to asIP-VRF-to-IP-VRFrouting because it enables inter-subnet routing at the leaf layer without requiring Layer 2 MAC learning for those specific prefixes.

Overlay Next Hop (Statement B):For a PE router to reach a prefix advertised via a Type 5 route, it must resolve theoverlay next hop. This next hop is typically the loopback IP address of the originating VTEP, which the receiving router uses to build the VXLAN tunnel.

Why others are incorrect:Statement A is incorrect because Type 7 routes are used for IGMP/MLD join synchronization. Statement D is incorrect because Type 5 routes advertise IP prefixes, not MAC addresses; MAC extended communities are associated with Type 2 routes.

To simplify VLAN management and automate the creation and pruning of VLANs across a network, Juniper utilizes theMultiple 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 ontrunk interfacesbetween 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 Bare incorrect because GVRP is legacy and no longer the recommended protocol for modern Junos deployments.Option Dis 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.

InPIM Sparse Mode (PIM-SM), theRendezvous 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 aPIM Registermessage.

When a receiver wants to join a group, its last-hop router sends a(*,G) PIM Joinrequest 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 Bis incorrect because PIM Dense Mode does not use an RP; it uses a "flood and prune" mechanism.Option Cis incorrect because the RP only forwards traffic to interfaces that have explicitly requested it via Join messages, which is what makes it "sparse".Option Dis incorrect because SSM (Source-Specific Multicast) specifically avoids using an RP by having receivers join a known source directly.

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.

In this scenario, router1 (AS 65001) is attempting to establish anExternal BGP (EBGP)peering with router2 (AS 65002) using theirloopback (lo0) interface addresses(192.168.1.1 and 172.16.1.1).

According to the Junos OS 24.4 documentation on BGP peering sessions:

EBGP TTL Default:By default, EBGP packets are sent with aTime-to-Live (TTL) value of 1. This assumes the peer is directly connected on a shared physical subnet.

Loopback Peering Challenge:When peering between loopback addresses, the destination IP is not on the same subnet as the physical ingress interface. Even if the routers are directly connected physically, the router treats the loopback interface as an additional "hop". With a TTL of 1, the BGP packet expires before it can be processed by the peer's routing engine.

The Multihop Solution (Option D):To allow this session to form, you must configure the multihop statement under the BGP neighbor hierarchy. This tells Junos to increase the TTL (the default becomes 64 when multihop is enabled) and allows the session to establish even though the peer's address is not directly connected.

Target Neighbor:The neighbor address specified in the configuration on router1 must be the remote loopback address of router2 (172.16.1.1).

Option A (Multipath)is incorrect because it is used for load balancing across multiple active BGP paths, not for initial session establishment.

Options B and Care incorrect because they reference physical interface addresses (10.10.20.1 or 10.10.10.1) which are not the addresses being used for the loopback-based BGP session.

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.