JN0-650 Exam Dumps - Enterprise Routing and Switching - Professional (JNCIP-ENT)

The exhibit shows router1 (AS 65001) connected to router2 (AS 65002) via two parallel physical links. The show bgp summary output indicates that sessions are established with two neighbors: 10.10.10.1 and 10.10.20.1. Currently, for the second neighbor (10.10.20.1), there are0 active routesdespite having4 accepted routes, which indicates that BGP has selected only one "best path" via the first neighbor for forwarding.

BGP Best Path Selection:By default, BGP only selects a single best path for any given destination prefix and installs that one path into the forwarding table. In a topology with parallel links to the same AS, this leads to underutilization of available bandwidth.

Multipath Solution (Option B):To enableactive routesfrom both peers and allow for load-balancing (ECMP) across both links, you must enable themultipathfeature.

When the multipath statement is configured under the protocols bgp group ext-peers hierarchy, it tells Junos OS to install multiple equal-cost BGP paths into the routing table and subsequent forwarding table.

Since both neighbors belong to the same peer group (ext-peers) and the same AS (65002), configuring multipath at the group level will apply to both sessions, allowing paths from both neighbors to be marked as "active".

Incorrect Options:

Option A:172.16.1.1 is the loopback address of router2. The exhibit shows peering is currently done using physical interface addresses (10.10.10.1 and 10.10.20.1), so this address is irrelevant to the current active sessions.

Option C:Configuring the neighbor address alone without the multipath parameter will not change the best-path selection behavior.

Option D:10.10.20.2 is the local interface IP of router1, not the neighbor's IP. BGP multipath must be configured to point to remote peer paths.

Configuration Example for Junos OS 24.4:To implement this, apply the following command: set protocols bgp group ext-peers multipath

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.

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.

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.