In an EVPN-VXLAN architecture, the interaction between the control plane (EVPN) and the data plane (VXLAN) is defined by specific functional components:
* VTEP (VXLAN Tunnel End Point): These are the entities responsible for the encapsulation and de- encapsulation of Layer 2 Ethernet frames into Layer 3 UDP/IP packets. A VTEP can be a physical switch (like a QFX or EX series) or a software-based entity. When traffic enters the fabric, the ingress VTEP wraps it in a VXLAN header; the egress VTEP removes this header before delivering it to the destination host. (Option B)
* VNI (Virtual Network Identifier): The VNI is a 24-bit field in the VXLAN header that allows for up to 16 million unique identifiers. It is used to identify specific broadcast domains (or VLANs) within the overlay network. Each VNI effectively represents a virtualized Layer 2 segment that is stretched across the Layer 3 underlay. (Option D)
* Incorrect statements: Option A is incorrect because VNIs are identifiers, not the "engine" that performs encapsulation-that is the VTEP's job. Option C is incorrect because VTEPs identify the endpoints of a tunnel, not the individual broadcast domains themselves.

In Junos OS 24.4, Captive Portal is used as a web-based authentication method for Layer 2 network access control, often in environments where 802.1X is not feasible for all users.
* Fallback Mechanism (Option D):On EX Series switches, Juniper supports aflexible authentication order. By default, the switch attempts authentication in the order of802.1X, thenMAC RADIUS, and finallyCaptive Portal. If a client fails both 802.1X and MAC RADIUS, the switch can fall back to Captive Portal to redirect the user to a login page.
* MAC Allowlist (Option B):Captive Portal relies on intercepting HTTP/HTTPS traffic to redirect users.
However, "headless" devices like printers or cameras lack web browsers and cannot interact with the portal. To accommodate these, Junos allows administrators to configure anauthentication allowlist(or whitelist), which identifies these devices by their MAC addresses and permits them to bypass the portal entirely.
* Precedence (Option A):This is incorrect because Captive Portal is generally thelastmethod in the default sequence, not the first.
* Layer 2 Participation (Option C):While Captive Portal requires a Layer 3 interface (RVI/IRB) for the redirection process, it is explicitly used to controlLayer 2 accesson EX Series switches.

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

OSPF determines the best path to a destination by calculating themetric (cost)of each link. By default, Junos OS uses areference bandwidthof100 Mbpsto 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 of1because 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 to10G(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 thelowest 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 Bis incorrect because a higher metric makes a pathlesspreferred.Option Cis incorrect because a 1G reference bandwidth would still result in both 1 GbE and 10 GbE interfaces having a cost of 1.

In a standard Layer 2 switch environment without specific multicast optimizations, multicast traffic is treated similarly to broadcast traffic and isflooded out of all portswithin a VLAN (except the port where it was received). This is inefficient as it consumes unnecessary bandwidth on ports where no receivers are present.
To optimize this,IGMP Snoopingis the standard solution.
* How it works:The switch "snoops" or monitors IGMP (Internet Group Management Protocol) messages between hosts and routers.
* Result:When a receiver sends an IGMP Membership Report (Join) for a specific multicast group, the switch records which port that request came from. It then builds a Layer 2 multicast forwarding table so that traffic for that group isonly forwardedto the specific ports that have active listeners.
* Junos OS 24.4 Configuration:On modern Juniper switches, you enable this globally or per VLAN using the set protocols igmp-snooping vlan <vlan-name> command.
Option A (Promiscuous mode)is used for monitoring or specific security configurations (like Private VLANs) and would not limit multicast flooding.Option B (Spanning Tree)manages loop prevention and does not differentiate between traffic types for forwarding optimization.Option D (IRB interface)is used for Layer 3 routing between VLANs but does not inherently provide Layer 2 multicast optimization within a single VLAN.