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

The exhibit shows a BGP routing process where anImport Policyis being applied to routes received in theRIB-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 ahidden 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 wererejected 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 Ais incorrect because it only shows accepted routes.

Option B and Care 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 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.

Junos OS 24.4 handles multicast traffic using two distinct models based on whether the source is known in advance.

Knowledge and Sources (Option A):PIM-ASM (Any Source Multicast)is designed for "many-to-many" communication where receivers join a group ($*,G$) and rely on a Rendezvous Point (RP) to discover active sources. In contrast,PIM-SSM (Source-Specific Multicast)is for "one-to-many" scenarios where receivers must alreadyknow the exact source IP($S,G$) before joining.

Protocol and RP Logic (Option D):PIM-SSMbypasses the RP entirely. It relies onIGMPv3messages from the host, which explicitly include both the source address and the group address. This allows the last-hop router to build a Shortest Path Tree (SPT) directly toward the source immediately.

Register Process (Option B):While PIM-ASM does use registers, it is the First-Hop Router (Designated Router on the source segment) that sends the register to the RP, not the receiver's DR.

RP Role (Option C):This is exactly backwards; PIM-ASMrequiresan RP for source discovery, whereas PIM-SSM does not use one at all.

In Junos OS, particularly in BGP-based environments like EVPN-VXLAN or MPLS, the router often needs to perform arecursive lookupto 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.

Theinet.3table 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 thesourceof 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.

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.

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.

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 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 portroles(isolated vs. community) rather than the method used to enable trunking between switches.

In BGP path selection, theLocal Preferenceattribute is one of the most common ways to influence outbound traffic from an Autonomous System (AS). It is a well-known discretionary attribute that is propagated throughout the AS to tell internal routers which path is preferred for a specific destination.

Priority Rule: In the BGP selection algorithm, ahigher local preferencevalue is always preferred over a lower one. The default value in Junos OS is100.

Influencing Outbound Traffic (Option A): To ensure that Provider A is always preferred, you would apply an import policy onR1(the router connected to Provider A) to set the local preference of all received routes to a value higher than the default (e.g., 200). Since 200 > 100, R3 and R4 will prefer the path via R1.

Alternative Method (Option C): Conversely, you can achieve the same result by applying an import policy onR2(the router connected to Provider B) to set the local preference to a value lower than the default (e.g., 50). Since the routes from R1 remain at the default of 100, and 100 > 50, the path via R1 (Provider A) is preferred.

Why B and D are incorrect: Setting a higher local preference on R2 (Option B) would make Provider B the preferred exit point. Setting a lower local preference on R1 (Option D) would make Provider A theleastpreferred exit point.

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.

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.

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, aVoice VLANmust 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 defaulton 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.

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.

In a three-stage EVPN-VXLAN fabric (Spine-Leaf architecture) where leaf devices perform the gateway services (Edge-Routed Bridging or ERB):

VTEP Functionality (Option B):Leaf devices act asVXLAN Tunnel End Points (VTEPs). They are responsible for encapsulating Ethernet frames from locally connected hosts into VXLAN packets for transport across the IP fabric and de-encapsulating incoming VXLAN packets.

Fabric Support (Option C):In a standard Juniper IP fabric design, both theleaf and spine devicesare typically expected to support VXLAN and EVPN capabilities. While spines in an ERB design might only perform IP forwarding in the underlay, they often participate in the BGP control plane (as Route Reflectors) or provide the ability to transition to Centrally-Routed Bridging (CRB) where spines would act as gateways.

Incorrect Options:Option Ais incorrect because the entire fabric infrastructure must be "VXLAN aware" in terms of MTU settings and routing capability to support the overlay.Option Dis incorrect because in an ERB design, the spine devices are high-speed transit nodes and do not terminate VXLAN tunnels; only the edge (leaf) devices act as VTEPs.

In a standard Layer 2 switch environment without specific multicast optimizations, multicast traffic is treated similarly to broadcast traffic and isflooded out of all portswithin a VLAN (except the port where it was received). This is inefficient as it consumes unnecessary bandwidth on ports where no receivers are present.

To optimize this,IGMP Snoopingis the standard solution.

How it works:The switch "snoops" or monitors IGMP (Internet Group Management Protocol) messages between hosts and routers.

Result:When a receiver sends an IGMP Membership Report (Join) for a specific multicast group, the switch records which port that request came from. It then builds a Layer 2 multicast forwarding table so that traffic for that group isonly forwardedto the specific ports that have active listeners.

Junos OS 24.4 Configuration:On modern Juniper switches, you enable this globally or per VLAN using the set protocols igmp-snooping vlan command.

Option A (Promiscuous mode)is used for monitoring or specific security configurations (like Private VLANs) and would not limit multicast flooding.Option B (Spanning Tree)manages loop prevention and does not differentiate between traffic types for forwarding optimization.Option D (IRB interface)is used for Layer 3 routing between VLANs but does not inherently provide Layer 2 multicast optimization within a single VLAN.