Juniper Enterprise Routing and Switching, Professional JN0-650 JNCIP-ENT Exam Questions

Answer : B

In External BGP (EBGP), there is a default safety mechanism that requires the peer's next hop to be on a directly connected network.

TTL Constraint: By default, EBGP packets are sent with a Time-to-Live (TTL) value of 1. If the next hop is not directly connected (e.g., when peering via loopback interfaces or across a multi-hop path), the packet will expire before reaching the destination, causing the route to be discarded or the session to fail.

The Multihop Solution (Option B): To override this behavior, you must configure the multihop statement under the BGP neighbor or group hierarchy. This allows the BGP session to establish by increasing the TTL (typically to 64 or a user-defined value) and bypasses the 'directly connected' check.

Incorrect Options: Option A (accept-remote-nexthop) is used in internal BGP or specific routing-instance scenarios to resolve next hops that aren't in the local routing table, but it doesn't solve the EBGP TTL/direct-connection requirement. Option C (advertise-inactive) allows BGP to advertise routes that are not the best path in the routing table, which is irrelevant to next-hop reachability. Option D (multipath) is used for load-sharing across multiple paths.

Answer : B, C

In Junos OS 24.4, the no-loss forwarding class is 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 use Priority-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 within forwarding 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 the suppression of tail drops rather than standard drop profiles.

Answer : C, D

The exhibit shows a BGP Route Reflector (RR) configuration where an export policy named NHS (Next-Hop Self) is applied to the internal BGP group int-group. The policy NHS sets the next-hop self attribute for BGP routes.

The Problem (Traffic Tromboning): In a standard BGP Route Reflector design, the RR should reflect routes without modifying the BGP next-hop attribute. By applying a next-hop self policy on the export to clients, the RR tells all its clients that it is the exit point for those routes. Consequently, all data plane traffic is sent to the RR first before being forwarded to the actual destination, rather than following the optimal direct path between clients. This is known as 'traffic tromboning' or suboptimal routing.

The Solution (Option C): The most direct way to fix this is to delete the export policy that is forcing the next-hop to be the RR. By deleting protocols bgp group int-group export NHS, the RR will resume standard behavior and reflect the original next-hop received from the route source, allowing clients to route traffic directly to the correct destination.

The Refined Solution (Option D): If you must keep the NHS policy (perhaps for routes learned from external peers), you should ensure it only applies to those specific routes. By adding from route-type internal to the policy term and then potentially changing the logic (or simply narrowing the scope), you can prevent the RR from incorrectly applying next-hop self to internal routes that it is merely reflecting. In the context of this specific problem, Option D combined with a change in the policy's action or scope helps ensure reflected internal routes maintain their original, optimal next-hops.

Option A is incorrect because setting next-hop self for external routes is common practice, but it doesn't solve the problem of internal reflected routes being diverted to the RR.

Option B is incorrect because applying this as an import policy would change how the RR itself sees the routes, but it wouldn't fix the attributes being sent out to the clients in the reflection process.

Answer : A, D

In Junos OS Class of Service (CoS), schedulers are the fundamental components used to manage the resources of individual egress queues. They determine how the switch handles traffic for a specific forwarding class as it waits to exit an interface.

Buffer Size (Option A): A scheduler defines the buffer size (memory allocation) for its assigned queue. This buffer holds packets during periods of congestion to prevent immediate packet loss. The size can be configured as a specific percentage of the total interface buffer, a temporal value in microseconds, or using the 'remainder' of available space.

Queue Priority (Option D): A scheduler identifies the priority of the queue. Junos supports multiple priority levels, such as low, medium-low, medium-high, and high. This setting dictates the order in which the transmission hardware services the queues; for example, high-priority queues are typically emptied before low-priority ones.

Why other options are incorrect: Interface rate-limiting (Option B) is typically managed at the interface level or through policers, not the scheduler itself, which focuses on queue-specific transmission rates. DiffServ code translation (Option C) is the responsibility of rewrite rules, which modify the packet header markings as they leave the switch.

Answer : B, D

When 802.1X server fail fallback is enabled with the vlan-name feature, the switch provides a specific survival mechanism for both existing and new sessions when the RADIUS server becomes unreachable.

Existing Clients (Statement B): Clients that have already successfully authenticated are unaffected by the server's unavailability in the short term. They maintain their current network access until their specific re-authentication timer expires. Only then will the switch attempt to contact the server again and trigger the fallback action if the server remains down.

New Clients (Statement D): For any new device attempting to connect while the RADIUS server is down, the switch cannot perform a standard authentication. Under the vlan-name fallback configuration, these new clients are automatically placed into the specified fallback VLAN and granted access based on the local policy defined for that VLAN.

Why others are incorrect: Statement A is incorrect because disconnecting active users would cause unnecessary service disruption. Statement C is incorrect because new clients cannot 'request' a VLAN during the 802.1X handshake; the switch assigns it based on the fallback configuration.

Answer : C

In a Juniper Q-in-Q (Layer 2 tunneling) environment, VLAN rewrites (specifically the swap operation) provide the most granular control over how customer traffic (C-VLANs) is mapped to service provider traffic (S-VLANs).

VLAN Rewrites (The Swap Operation): This method involves replacing the incoming customer VLAN tag with a service provider tag as the frame enters the tunnel. This is technically a 'swap' because the original C-VLAN tag is removed and the S-VLAN tag is written in its place. At the egress of the tunnel, the S-VLAN tag is swapped back for the original C-VLAN tag. This is often used when different customers use the same C-VLAN IDs and the provider needs to keep them unique within their core.

Many-to-Many: This is a mapping style where multiple customer VLANs are mapped to multiple service provider VLANs, but it typically relies on the 'push' (stacking) operation rather than a literal 'swap' of the tag itself.

All-in-One: This is the simplest form of Q-in-Q where all traffic entering an interface is 'pushed' into a single S-VLAN tag, regardless of any existing C-VLAN tags. No swapping occurs; the original tags are simply buried under the new provider tag.

L2PT (Layer 2 Protocol Tunneling): This is a feature used to tunnel Layer 2 control protocols (like STP, CDP, or LLDP) across a provider network by encapsulating them or changing their destination MAC addresses. It does not involve the swapping of VLAN tags.

Answer : C

Junos OS 24.4 on EX Series switches provides robust support for LLDP (Link Layer Discovery Protocol) and its extension, LLDP-MED (Media Endpoint Discovery).

LLDP-MED Power Negotiation: This feature allows a switch (Power Sourcing Equipment or PSE) and a connected device (Powered Device or PD), such as an IP phone or access point, to negotiate power requirements beyond the standard IEEE 802.3af/at classes. The switch can dynamically allocate the exact amount of power the device needs (in 0.1W increments), which optimizes the power budget of the switch.

LLDP Scope: LLDP is a Link Layer protocol (Layer 2), but it is not restricted to Layer 2 interfaces; it can also operate on Layer 3 interfaces to advertise system identity and capabilities. This makes Option A incorrect.

Link-Local Protocol: LLDP frames use a specific multicast MAC address (01:80:c2:00:00:0e) that is not flooded or forwarded by switches. They are strictly link-local between two directly connected neighbors. This makes Option B incorrect.

Endpoint Focus: LLDP-MED is specifically designed for Media Endpoint Devices (like VoIP phones), providing TLVs for network policy (VLAN/QoS), location identification, and inventory management. Standard LLDP is used for discovering network connectivity devices. This makes Option D incorrect.