Juniper JN0-650 Enterprise Routing and Switching - Professional (JNCIP-ENT) Exam Practice Test

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.

In an EVPN-VXLAN environment, different BGP route types serve distinct purposes in building the control plane. TheEthernet Segment Identifier (ESI)is a unique 10-byte identifier used to represent a multi-homed segment.

Type 1: Ethernet Auto-Discovery (A-D) Route (Option A):This route type is essential for multi-homing scenarios. It carries theESIto support features likefast convergenceandaliasing. By advertising an A-D route per Ethernet Segment, a PE tells other routers that it is connected to that specific ESI. It doesnotcarry individual host MAC addresses; instead, it provides a "mass withdraw" mechanism to quickly update paths if the entire segment goes down.

Type 4: Ethernet Segment Route (Option D):This route is used exclusively forDesignated Forwarder (DF) election. It advertises the existence of anESIand the ES-Import Route Target to all other PE routers. This allows PE routers connected to the same multi-homed segment to discover each other automatically and elect a DF to handle BUM traffic. Like Type 1, it focuses on the segment identity and doesnotinclude MAC addresses.

Type 2: MAC/IP Advertisement Route (Option B):This is the primary route used for host reachability. Itmustinclude a MAC address (and optionally an IP). While it also includes the ESI to indicate which segment the host is behind, its primary function is MAC advertisement.

Type 3: Inclusive Multicast Ethernet Tag Route (Option C):This route is used for VTEP discovery and building the replication list for BUM traffic. It identifies the VTEP's IP and the VNI, but it doesnotcarry the ESI or MAC addresses.

Junos OS 24.4 provides several server-failover options for 802.1X authentication to maintain network availability when the RADIUS server is unreachable.

Fallback Behavior (Option D):Theuse-cachefallback action allows the switch to consult its local cache of previously authenticated MAC addresses.

If a device was already authorized and its information is in the cache, the switch willcontinue to permit accessbased on those cached credentials.

However, if a new device (not in the cache) attempts to connect while the server is down, the switch cannot verify its credentials and willdeny the access attempt. This matches the specific requirement to permit authorized devices while denying new ones.

Other Fallback Options:

permit (Option C):This would allowalldevices (even new ones) to access the network, typically in a restricted "guest" or "bypass" VLAN.

deny (Option A):This would drop all traffic from all devices on the port if the server is unreachable.

vlan-name (Option B):This moves authenticated or unauthenticated users into a specific fallback VLAN.

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.

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 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 standard BGP operations, a router typically selects only one "best path" for a given destination prefix and installs that single path into the forwarding table. To utilize multiple paths for traffic forwarding (load-balancing), specific multipath features must be enabled.

BGP Multipath:This feature allows a router to install multiple equal-cost paths into the routing and forwarding tables. However, by default, BGP multipath requires that all candidate paths have the same neighboring Autonomous System (AS).

Multipath Multiple-AS (Option B):In the exhibit, R1 is receiving routes fromISP A (AS 65501)andISP B (AS 65502). Since these are two different neighboring ASs, the standard multipath feature is not sufficient. You must use the multipath multiple-as statement under the BGP group or neighbor hierarchy. This tells Junos to consider paths as equal even if they originate from different neighboring ASs, provided all other BGP path selection attributes (Local Preference, AS Path length, Origin, MED, etc.) are identical.

Why other options are incorrect:*Option A (multihop)is used for peering with routers that are not directly connected.

Option C (prefix limit)is a security and stability feature to limit the number of prefixes received from a neighbor.

Option D (damping)is used to penalize unstable, "flapping" routes to prevent constant routing table churn.

Configuration Example for Junos OS 24.4:To implement this on R1, you would use the following configuration:

set protocols bgp group multipath multiple-as

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, a physical or logical interface is typically associated with a single OSPF area. However, there are specific design requirements—such as migrating an interface from one area to another without downtime or creating specific transit topologies—where an interface needs to exist in two areas simultaneously.

Multi-area Adjacency (Option B):The secondary command under the OSPF interface hierarchy allows an interface to be part of asecondary areain addition to its primary area.

Protocol Behavior:When an interface is configured as secondary, the router sends and receives OSPF Hello packets for both the primary and secondary areas on that single link. This allows the router to form adjacencies with neighbors in both areas over the same physical connection.

Use Case:This is frequently used in hub-and-spoke topologies or during network restructuring to ensure reachability is maintained while changing area boundaries. It effectively allows a "logical" split of the interface at the OSPF protocol level.

The exhibit shows a multicast network runningPIM Sparse Modewhere R2 is configured as a localRendezvous Point (RP). However, the non-RP routers (like R5) show no learned RP in their show pim rps output. To resolve this usingstandard protocolsfor dynamic RP discovery, you must implement a mechanism that automates the distribution of RP information across the PIM domain.

Bootstrap Router (BSR) (Option B):BSR is the industry-standard (RFC 5059) mechanism for dynamically electing an RP and distributing that information throughout a PIM-SM domain.

It uses two roles:Candidate-RPs (C-RPs), which announce their desire to be an RP, andCandidate-BSRs (C-BSRs), which collect these announcements and flood them to all other routers in the network via PIM bootstrap messages.

BSR is a "standard protocol" as it is part of the PIMv2 specification. Once configured on R2 (as C-RP) and potentially R1 or R2 (as C-BSR), all other routers will dynamically learn that R2 is the RP for the specified group ranges.

Auto-RP (Option D):While this also provides dynamic RP discovery, it is aproprietaryCisco protocol. Although Junos supports it for interoperability, the question specifically asks for "standard protocols only," making BSR the preferred choice.

MSDP (Option A):Multicast Source Discovery Protocol (MSDP) is used to share information about active sources betweendifferentPIM domains or for Anycast-RP. It does not handle the initial discovery of an RP within a single domain for standard PIM-SM operations.

Anycast RP (Option C):This is a technique used for RP redundancy and load balancing. While it can use BSR or MSDP for synchronization, it is a design architecture rather than a standalone "standard protocol" for the basic dynamic discovery of an RP in the manner requested here.

Configuration Example for BSR in Junos OS 24.4:To enable this, you would add the following to the RP (R2):

set protocols pim rp bootstrap-discovery

set protocols pim rp candidate-rp 10.222.1.2 group-ranges 224.0.0.0/4

set protocols pim rp candidate-bsr 10.222.1.2

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.

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.

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 aLimitset toexact.

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

Option Dis 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.

To provide IP phones with geographic location details (such as civic addresses or coordinates) automatically, Juniper EX Series switches utilize theLLDP-MED (Link Layer Discovery Protocol - Media Endpoint Discovery)protocol.

VoIP Specifics:While standard LLDP (C) is for general device discovery,LLDP-MEDis an enhancement specifically designed for network-to-endpoint communication for VoIP devices.

Location Identification:LLDP-MED supportsLocation Identification TLVs(Type-Length-Values). These allow a switch to push geographic or civic location data to an IP phone, which is critical for E911 services and asset tracking.

Junos Implementation:On EX Series switches, this is typically configured under protocols lldp-med to ensure the switch advertises the necessary location information to connected endpoints.

The exhibit shows the output of the command show route protocol bgp on router R1 for the prefix 172.16.10.1/32. To determine the correct characteristics of this route, we analyze the specific BGP attributes and next-hop information provided in the routing table entry:

Multipath Parameter (Option B): The routing table shows two distinct paths for the prefix 172.16.10.1/32. The first path has two next hops (192.168.10.1 and 192.168.20.1) and is marked with the plus symbol (+) and the asterisk (*), indicating it is both an active and the best route. The presence of multiple next hops being used simultaneously for a single BGP path is a clear indication that the multipath parameter is enabled in the BGP configuration. In Junos OS, BGP multipath allows the installation of multiple equal-cost BGP paths into the forwarding table to facilitate load balancing.

Available Next Hops (Option C): The output explicitly lists two functional next hops for the active path: 192.168.10.1 via ge-1/0/0.2 and 192.168.20.1 via ge-1/0/1.3. Both show an outgoing interface, confirming that this route has two next hops available for traffic forwarding.

IBGP vs. EBGP (Option A): The BGP routes shown have an AS path of 200 I. This indicates the routes were learned from an external Autonomous System (AS 200). Furthermore, the protocol preference is 170. In Junos OS, the default preference for External BGP (EBGP) is 170, whereas the default preference for Internal BGP (IBGP) is 200. Therefore, this configuration is for EBGP, not IBGP.

Hidden Next Hops (Option D): The summary line at the top of the exhibit mentions that there are "2 hidden" routes in the inet.0 table. However, these hidden routes are not the next hops for the 172.16.10.1/32 prefix. A hidden route is a prefix that was rejected by policy or has an unreachable next hop; it is not a "hidden next hop" belonging to an active route.

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 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 consideredterminalif 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 policyexecutes that action immediatelyand 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.

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.

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.