Pass the Juniper JNCIP-ENT JN0-650 Questions and answers with CertsForce

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.

Junos OS uses specific routing tables for handling multicast traffic to ensure loop prevention through Reverse Path Forwarding (RPF) checks:

Multicast RPF (Option C):Theinet.0table is the default unicast routing table. In most standard multicast deployments, Protocol Independent Multicast (PIM) performs itsRPF checksagainst this table to determine the upstream interface toward the multicast source.

Topology Differences (Option A):Theinet.2table is specifically designed for multicast RPF lookups when themulticast forwarding topology differsfrom the unicast forwarding topology. This is common in environments using Multiprotocol BGP (MBGP) where you might want multicast traffic to follow a different path than standard data traffic.

inet.1 Role (Option B):Theinet.1table is themulticast forwarding cache. It stores (S,G) and (*,G) entries for actual packet forwarding. Routing protocols like MBGP or IS-IS do not place routesdirectlyinto inet.1; instead, PIM uses information from inet.0 or inet.2 to populate inet.1.

IS-IS and OSPFv3 (Option D):These protocols place their IPv4/IPv6 unicast routes into inet.0 or inet6.0. They do not place routes into inet.2 "directly" unless specific RIB-group configurations or address families are enabled to share those routes for multicast RPF purposes.

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.

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.

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.

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 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 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.

OSPF stub areas are used to reduce the size of the Link-State Database (LSDB) in routers with limited resources by restricting the flooding of external routes.

Virtual Links (Option C):According to OSPF standards (both v2 and v3),virtual links cannot pass through stub areas. A virtual link must transit a "transit area," which must be a standard (non-stub) area with a full routing table.

Totally Stubby Areas (Option D):A stub area (which blocks Type 5 External LSAs) can be further restricted into atotally stubby area. In Junos OS, this is done by adding the no-summaries statement to the stub configuration. This blocks both Type 5 and Type 3 (Inter-area) LSAs, replacing them with a single default route.

Incorrect Statements:Option Ais incorrect because standard stub areas cannot contain an ASBR; only Not-So-Stubby Areas (NSSA) allow for an ASBR.Option Bis incorrect because an area is either a Stub or an NSSA; they are mutually exclusive configurations for the same area.

The exhibit illustrates an Autonomous System (AS 65512) receiving the same prefix ($203.0.113.0/24$) from two different neighbors, ISP A and ISP B. To influence outbound traffic from AS 65512 so that ISP A is preferred, you must manipulate the BGP Local Preference attribute.BGP Path Selection and Local Preference: Local preference is the first attribute evaluated by BGP after checking if the next hop is reachable. A higher local preference value is always preferred over a lower one. The default value in Junos OS is 100.Applying the Preference (Option B): By applying an import policy on router R1 to set a local preference higher than 100 (e.g., 200) for routes from ISP A, R1, R2, and R3 will all prefer the path through R1 to reach ISP A.Applying the Preference (Option C): Alternatively, you can achieve the same result by applying an import policy on R2 to set a local preference lower than 100 (e.g., 50) for routes from ISP B. Since the routes from R1 remain at the default of 100, the path through ISP A (100) will be preferred over ISP B (50).Why A and D are incorrect: Setting a lower preference for ISP A (Option A) or a higher preference for ISP B (Option D) would result in ISP B being preferred for outbound traffic, which is the opposite of the requirement.