When integrating a QFX Series switch into an EVPN-VXLAN IP fabric, specific BGP and EVPN hierarchy configurations are required to establish the control and data planes:
EVPN Encapsulation (Option A): In Junos OS, the encapsulation vxlan statement must be explicitly configured under the protocols evpn hierarchy. This defines that the EVPN control plane will use VXLAN as the data plane encapsulation method rather than MPLS.
BGP Address Family (Option C): EVPN uses Multiprotocol BGP (MP-BGP) to distribute reachability information. For the control plane to function, you must enable the EVPN signaling address family under the BGP protocol using the command set protocols bgp group < name > family evpn signaling.
Incorrect Options: Option B is incorrect because family vpls is used for traditional VPLS signaled by BGP, not for EVPN-VXLAN. Option D is incorrect because while the loopback interface must be reachable, it is typically advertised via an IGP (like OSPF or IS-IS) to provide the underlay connectivity that BGP then rides upon; BGP itself does not " advertise " the loopback to establish the initial peerings.

OSPF determines the best path to a destination by calculating the metric (cost) of each link. By default, Junos OS uses a reference bandwidth of 100 Mbps to calculate this cost using the formula:

When the reference bandwidth is left at the default 100 Mbps, any interface with a speed of 100 Mbps or higher (including 1 GbE and 10 GbE) is assigned a cost of 1 because the minimum OSPF cost is 1. This results in equal-cost paths, preventing the router from preferring the faster 10 GbE link.
To ensure 10 GbE interfaces are preferred, you must create a cost differential:
Option A (Reference Bandwidth): By increasing the reference bandwidth to 10G (or higher), the calculation changes. For a 10 GbE link, the cost becomes $10,000 / 10,000 = 1$. For a 1 GbE link, the cost becomes
$10,000 / 1,000 = 10$. Since OSPF prefers the path with the lowest cumulative cost, the 10 GbE link is now preferred.
Option D (Manual Metric): You can manually override the automatic cost calculation by assigning a higher metric specifically to the 1 GbE interfaces. If a 1 GbE interface is manually set to a cost of 50 and the 10 GbE interface remains at 1 (or is set to a lower value), the router will prioritize the 10 GbE path.
Option B is incorrect because a higher metric makes a path less preferred. Option C is incorrect because a 1G reference bandwidth would still result in both 1 GbE and 10 GbE interfaces having a cost of 1.

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.

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 use Multifield (MF) classifiers because incoming traffic often lacks markings. MF classification assigns traffic to an internal forwarding class based on multiple fields (IPs, ports, etc.). Core devices use Behavior Aggregate (BA) classifiers because 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 implement rewrite rules on the egress interfaces of 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 the next hop.
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) 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 < interface > 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 port roles (isolated vs. community) rather than the method used to enable trunking between switches.