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

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.

OSPF (Open Shortest Path First) is a standards-based Link-State Interior Gateway Protocol (IGP) implemented within Junos OS 24.4:

Intra-AS Routing:OSPF is designed to distribute routing information and performneighbor discovery within a single Autonomous System (AS). It divides the AS into areas to localize Link-State Advertisements (LSAs) and reduce the size of the Link-State Database (LSDB) on each router. (Option B)

Algorithm:OSPF uses theShortest Path First (SPF) or Dijkstra algorithm, not a distance vector algorithm (which would be RIP or BGP). This makesOption Aincorrect.

Directly Connected Routes:In Junos OS, you must explicitly configure an interface under the [edit protocols ospf] hierarchy to include it in the OSPF process. Once an interface is added, its prefix isautomatically advertisedto neighbors via Router (Type 1) LSAs. This makesOption Ctechnically inaccurate in the context of interfaces participating in the protocol.

Scope:Protocols used between multiple autonomous systems are External Gateway Protocols (EGPs), such as BGP. This makesOption Dincorrect.

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 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.

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 Junos OS 24.4, theno-loss forwarding classis used for traffic that requires lossless delivery, such as iSCSI or FCoE, typically in a Data Center Bridging (DCB) environment.

Priority-Based Flow Control (Option C):To guarantee "no-loss" behavior, the switch must support and usePriority-based Flow Control (PFC). PFC allows the switch to send "pause" frames for a specific priority (forwarding class) to prevent buffer overflow and packet drops without affecting other traffic on the same link.

Forwarding Class Sets (Option B):In enhanced Layer 2 software (ELS) versions used by modern QFX and EX series switches, lossless traffic must be managed withinforwarding class sets(also known as priority groups). This grouping is necessary to apply specific DCB properties, such as PFC and specific bandwidth guarantees, to the lossless traffic class.

Why A and D are incorrect:Default scheduler maps and default drop profiles do not provide the specialized buffer management or lossless signaling required for this class. Lossless traffic specifically requires thesuppression of tail dropsrather than standard drop profiles.

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 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.

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.

The IETF standards for EVPN-VXLAN define the scalability and forwarding behavior of the architecture.

VXLAN Scale (Statement B):The Virtual Network Identifier (VNI) is a24-bit fieldin the VXLAN header. This allows for up to $2^{24}$ unique identifiers, which translates to approximately16 milliondistinct VXLAN broadcast domains (segments) within a single fabric. *Forwarding Behavior (Statement D):VXLAN is a MAC-in-UDP encapsulation technology. When a Layer 2 frame enters the tunnel at a VTEP, theoriginal Layer 2 frame(including the original source and destination MAC addresses) is encapsulated into a UDP/IP packet and transported across the IP underlay. When it reaches the egress VTEP, the header is removed and theLayer 2 frame is forwarded unchangedto the destination host.

Why others are incorrect:Statement A is incorrect because EVPN itself can technically support more than 16 million domains, but the data plane (VXLAN) is the limiting factor in this specific deployment scenario. Statement C is incorrect because VXLAN encapsulates Layer 2 frames, not just "IP packets," and it treats the entire frame as a payload.