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

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.

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 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

The exhibit shows a network topology whereMultiple VLAN Registration Protocol (MVRP)is used to dynamically manage VLANs across switches Core-1, Access-1, and Access-2.

Identifying the Missing Configuration:According to the diagram, the trunk link betweenCore-1andAccess-2uses interfacege-0/0/16.0on the Core-1 side.

Output Analysis:However, the show protocols mvrp output for Core-1 only lists interfaces ge-0/0/14.0 and ge-0/0/15.0.

MVRP Requirements:For MVRP to successfully propagate VLAN information between Access-2 and the rest of the network, the protocol must be enabled on every trunk interface in the path.

Solution:Becausege-0/0/16.0is missing from the Core-1 MVRP configuration, VLAN registration messages from Access-2 are not being processed by Core-1. Configuring this interface under MVRP on Core-1 will solve the communication problem.

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 Junos OS, the supplicant-mode configuration under protocols dot1x determines how the switch handles multiple MAC addresses on a single physical port. According to the exhibit, the current mode is set toSingle, and theNumber of connected supplicantsis2. This indicates thatthe port is currently allowing multiple devices, which contradicts the goal of limiting access to only one device at a time.

Here is the breakdown of whyOption Cis the correct solution based on Juniper’s standard behavior:

Supplicant Mode: Single (Current State):In this mode, the first device to authenticate opens the port for all subsequent devices. As long as the first device remains authenticated, other devices can send traffic through the port without individual authentication. This is why the exhibit shows 2 connected supplicants despite the mode being "Single."

Supplicant Mode: Single-Secure (The Solution):This mode strictly limits the port toonly oneMAC address. Once a device successfully authenticates via 802.1X, the switch drops any traffic coming from any other MAC address on that port. If the authenticated device logs off or the session times out, the port becomes available for a new device, but never more than one simultaneously. *Supplicant Mode: Multiple (Option B):This mode allows multiple supplicants to authenticate individually. Each MAC address must go through its own authentication process. This would allow more than one device, which is the opposite of the user's requirement.

MAC RADIUS Restrict (Option A):This feature is used to force MAC-based authentication and does not inherently limit the number of devices to one in the same way that changing the supplicant mode does.

Maximum EAPOL requests (Option D):This parameter defines how many times the switch will send an EAP-Request/Identity frame to a supplicant before giving up. Changing this to 1 does not restrict the number of devices allowed on the port; it only changes the retry logic for a single authentication attempt.

Configuration Example for Junos OS 24.4:To implement this change, you would use the following command: set protocols dot1x edit interface ge-0/0/10.0 supplicant-mode single-secure

This scenario describes the standard transition of Class of Service (CoS) metadata from the network edge to the network core.

MF vs. BA Classification:Edge devices useMultifield (MF) classifiersbecause incoming traffic often lacks markings. MF classification assigns traffic to an internalforwarding classbased on multiple fields (IPs, ports, etc.). Core devices useBehavior Aggregate (BA) classifiersbecause they are faster; they only look at the CoS bits (like DSCP) in the header to determine the forwarding class.

The Problem:Internal forwarding class assignments made by an MF classifier on the edge device do not automatically travel with the packet. If the packet leaves the edge device with its original (potentially zeroed) DSCP bits, the core device's BA classifier will not be able to identify the priority.

The Solution (Option A):You must implementrewrite ruleson theegress interfacesof the edge devices. A rewrite rule takes the internal forwarding class and loss priority assigned by the MF classifier and "writes" the corresponding DSCP value into the packet header as it exits toward the core. This ensures that the core device sees the correct DSCP marking and can apply the appropriate BA classification.

Incorrect Options:Rewrite rules are strictly an egress function to modify the packet for thenexthop. Applying them on ingress (Option B) or core ingress (Option C) does not solve the problem of ensuring the packet header reflects the classification logic used during the internal switching process of the edge device.

Private VLANs (PVLANs) allow for granular port isolation within a single broadcast domain. When extending a PVLAN across multiple switches (S1 to S2), the secondary VLANs (Community or Isolated) must be preserved across the trunk links.

802.1Q Tagging (Option B):For traffic from aCommunity VLAN (RND)to reach members on a different switch, the Community VLAN must have its own802.1Q VLAN tag (VLAN ID)associated with it. When a frame from a community port on S1 traverses the trunk to S2, it is tagged with this specific secondary VLAN ID. S2 receives the tagged frame, identifies it as belonging to the RND community, and forwards it to the appropriate community or promiscuous ports.

Why it fails without a tag:If the RND community is only defined locally on S1 without a global VLAN ID, the trunk port will not know how to distinguish that traffic from the Primary VLAN or other communities.

Incorrect Options:Option Ais incorrect because the community VLANmusthave a different tag than the parent (Primary) VLAN to maintain the internal PVLAN logic.Option Cis incorrect because stripping tags would lead to the traffic being merged into the native VLAN or dropped.Option Dis incorrect because RND is a community VLAN; changing it to an isolated VLAN would change its behavior (preventing communication between members of that same group).

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.

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.