This question tests the understanding of Junos scheduler parameters, specifically transmit-rate and excess-rate.

Option D is correct because the transmit-rate for queue 2 is 10%. This value represents the guaranteed minimum bandwidth for the queue. During periods of sustained network congestion, the scheduler ensures this queue receives at least 10% of the interface bandwidth. Any traffic attempting to use more than its allocated bandwidth (guaranteed plus its share of excess) will cause the queue's buffer to fill, leading to packet drops. The statement correctly implies that traffic above the 10% guarantee is not assured service and is subject to being dropped.

Option A is correct due to a likely, albeit technically imprecise, interpretation by the question author. The transmit-rate (the actual bandwidth reservation) for queue 0 is 10%. However, the excess-rate is configured at 76%. This parameter determines that queue 0 will receive a 76% weighted share of any available excess bandwidth. Given that other options are demonstrably false, it is probable the question incorrectly uses the term "bandwidth reservation" to refer to the configured excess-rate value.

B: During times of no congestion, a queue can use up to the full interface bandwidth if it is available; the transmit-rate is a minimum guarantee, not a maximum limit.

C: The configured bandwidth reservation (transmit-rate) for queue 0 is explicitly set to 10%, not 100%.

1. Juniper Networks TechLibrary, Junos OS 23.4, Class of Service Configuration Guide, "Configuring Schedulers." This guide defines the key parameters. It states, "transmit-rate—Defines the minimum amount of bandwidth allocated to a queue... also determines the amount of excess (extra) bandwidth the queue can share... excess-rate—Percentage of the non-guaranteed (excess) bandwidth to be used by the queue." This supports that the 10% for queue 2 is its guaranteed rate (relevant to option D) and that the 76% for queue 0 is its excess sharing weight (relevant to the interpretation of option A).

2. Juniper Networks TechLibrary, Junos OS 23.4, Class of Service User Guide, "Understanding CoS Schedulers." This document explains the behavior during congestion. It clarifies, "During periods of congestion, the transmit rate is the guaranteed bandwidth for the queue." This directly supports the reasoning for option D, where congestion enforces the 10% guarantee for queue 2, and traffic beyond that is at risk. It also states, "When there is no congestion, a queue can receive more bandwidth than its guaranteed minimum if bandwidth is available," which directly refutes option B.

In Protocol Independent Multicast Sparse Mode (PIM-SM), the Rendezvous Point (RP) acts as a shared root for a multicast distribution tree. Its primary role is to be a central "meeting point" for sources and receivers. A multicast source's designated router (DR) registers the active source with the RP. Concurrently, a receiver's DR sends PIM join messages toward the RP to express interest in a multicast group. The RP is responsible for connecting the registered sources to the interested receivers, initiating the flow of multicast traffic along this shared tree. This mechanism avoids flooding the network, which is characteristic of dense mode.

B. PIM dense mode operates on a flood-and-prune model and does not use a Rendezvous Point (RP); RPs are fundamental to sparse mode operation.

C. This describes network flooding. PIM sparse mode is an explicit-join model where traffic is only forwarded toward interested receivers, not to all interfaces.

D. Source-Specific Multicast (SSM) is a distinct multicast model that completely eliminates the need for an RP by having receivers join a specific (Source, Group) channel directly.

1. Juniper Networks TechLibrary, "Understanding PIM Sparse Mode": "In sparse mode, routers must join and leave multicast groups explicitly. The designated router sends a join message to the rendezvous point (RP). The RP is responsible for keeping track of multicast group members and serves as the meeting point for multicast sources and receivers." This directly supports the role described in option A.

2. Juniper Networks TechLibrary, "PIM Overview": "PIM-SM is an explicit-join protocol that is optimized for environments where there are many multicast groups, but receivers for any particular group are sparsely distributed... PIM-SM uses a central point of contact, called a rendezvous point (RP), for sources and receivers to 'meet'." This confirms the function of the RP as a meeting point and contrasts it with dense mode, invalidating option B.

3. Juniper Networks TechLibrary, "Source-Specific Multicast Overview": "SSM differs from other multicast modes because it builds a shortest-path tree (SPT) from the receiver to the source, without the need for a rendezvous point (RP)." This statement confirms that SSM is a model that operates without an RP, making option D incorrect.

In an EVPN-VXLAN multihoming active-active scenario, a Designated Forwarder (DF) is elected per Ethernet Segment (ES) to handle Broadcast, Unknown Unicast, and Multicast (BUM) traffic. The DF is the only device that forwards BUM traffic from the VXLAN core to the multihomed device.

In this case, leaf2 is the DF. When server2 sends a broadcast frame, leaf2 forwards it locally to server1. leaf1 is the non-DF, so it is prohibited from forwarding any BUM traffic received from the core to server1. As an optimization, since leaf1 would drop the frame anyway, leaf2 may not forward the BUM frame to leaf1 at all. Consequently, only leaf2 forwards the frame to server1.

A. The broadcast frame will be forwarded to leaf1 and Ieaf2.

This is incorrect. The frame originates from a server connected to leaf2; it is not forwarded to leaf2. It is also not forwarded to leaf1 due to the non-DF role and potential pruning.

D. Only leaf1 will forward the broadcast frame to server1.

This is incorrect. leaf1 is the non-DF for the Ethernet Segment and is explicitly required to drop BUM traffic for that segment to prevent

The command show route receive-protocol bgp is the correct tool to verify the routes being advertised by a BGP peer before they are processed by the local router's import policies. This command displays the BGP path attributes, including the AS path, for all prefixes received from that neighbor. This directly allows an administrator to see that the 0.0.0.0/0 route is "coming from AS 64512" as it was advertised. While the exhibit shows the route after it has been selected and installed in the inet.0 routing table, the receive-protocol command is the specific function to inspect the raw advertisements from a peer.

B. show route protocol bgp source-gateway is not a valid command syntax in the Junos OS.

C. show route protocol bgp next-hop is not a valid command syntax in the Junos OS.

D. The hidden keyword is used to display received routes that are not considered for path selection (e.g., due to an invalid next-hop). The route in the exhibit is active, as indicated by the asterisk (), not hidden.

1. Juniper Networks TechLibrary - show route receive-protocol: "Use this command to display the routes that a BGP routing device has received from a neighbor, before the routing policy is applied." This documentation confirms that this command is used to inspect incoming advertisements from a peer, which includes the AS path attribute. (Source: Juniper Networks TechLibrary, CLI Explorer, show route receive-protocol).

2. Juniper Networks TechLibrary - show route: The documentation for the show route command and its variants (show route protocol bgp) does not list source-gateway or next-hop as valid keywords, confirming options B and C are incorrect. The hidden option is described for displaying routes that are not eligible to become active. (Source: Juniper Networks TechLibrary, CLI Explorer, show route).

3. Junos Routing Protocols Configuration Guide - Monitoring BGP: This guide details the use of operational mode commands for BGP. It specifies show route receive-protocol bgp peer-address as the method to "View the routes that the local router has received from the BGP peer before the routing policy has been applied." (Source: Junos OS 22.4, Routing Protocols Configuration Guide, Section: "Monitoring BGP Configuration and Operation").

When 802.1X is configured with server-fail fallback on a Juniper EX Series switch and the RADIUS server becomes unavailable, the switch's behavior is twofold. First, for clients that are already authenticated, their sessions are not immediately terminated. They remain connected and can continue to pass traffic until their session timer expires and a re-authentication attempt is required. Second, for any new clients attempting to connect, the fallback mechanism is triggered. Since the vlan-name feature is specified, these new clients are automatically placed into the configured fallback VLAN and granted network access within that segment.

A. An outage of the RADIUS server does not trigger an immediate disconnection of currently authenticated clients; their sessions remain active until re-authentication is attempted.

C. The client does not "request" a VLAN in this context. The switch enforces the configured fallback VLAN for all new clients, regardless of any client-side settings.

1. Juniper Networks TechLibrary, Junos OS Documentation, "Understanding 802.1X Server Fail Fallback":

"If the RADIUS servers are unavailable, supplicants that are already authenticated on the port are not affected. These supplicants remain connected to the LAN." (This supports option B and refutes option A).

"When the RADIUS authentication server is unavailable... you can configure the switch to provide supplicants with access to a limited network or to a specific VLAN." (This supports option D).

2. Juniper Networks TechLibrary, Junos OS Documentation, "Configuring 802.1X Server Fail Fallback (CLI Procedure)":

Under the server-fail hierarchy level, the vlan-name option is described as: "Specifies the VLAN to which the supplicant is moved if the RADIUS server is unavailable." (This directly supports the action described in option D).

Multiple VLAN Registration Protocol (MVRP) dynamically propagates VLAN information between switches. For MVRP to function correctly across a network, it must be enabled on all trunk interfaces that are part of the desired Layer 2 path. The provided configuration for Core-1 only enables MVRP on interface ge-0/0/15.0, which connects to Access-1. To allow VLANs to be propagated to and from Access-2, MVRP must also be enabled on the trunk interface on Core-1 that connects to Access-2, which is ge-0/0/16.0. This ensures that VLAN registration messages can be exchanged across the entire path.

A. The choice of spanning tree protocol (RSTP vs. VSTP) is unrelated to the VLAN propagation failure caused by the incomplete MVRP configuration.

B. MVRP is designed for inter-switch trunk links to manage VLAN propagation, not for host-facing access interfaces. Configuring it on access ports is incorrect.

D. Similar to option B, enabling MVRP on access interfaces is an improper configuration and would not solve the trunk link propagation issue.

1. Juniper Networks. (2023). Understanding Multiple VLAN Registration Protocol (MVRP) for VLANs. TechLibrary. In the "MVRP Operation" section, it states, "To enable MVRP, you must configure it on all trunk interfaces on all switches that you want to participate in MVRP." This confirms that MVRP must be enabled on all relevant trunk ports. Retrieved from https://www.juniper.net/documentation/us/en/software/junos/vlan-l2/topics/concept/mvrp-understanding.html

2. Juniper Networks. (2023). Configuring MVRP (CLI Procedure). TechLibrary. Step 2 of the "Step-by-Step Procedure" shows the command set protocols mvrp interface interface-name and includes the instruction, "Repeat this step for all trunk interfaces that will participate in MVRP." This directly supports the need to configure the interface to the second access switch. Retrieved from https://www.juniper.net/documentation/us/en/software/junos/vlan-l2/topics/task/mvrp-configuring.html

In an EVPN-VXLAN edge-routed bridging (ERB) architecture, the Layer 3 gateway functionality is distributed to the edge devices (leaf or distribution switches). This model uses a distributed anycast gateway, where all participating leaf switches are configured with the same IP address and MAC address on their Integrated Routing and Bridging (IRB) interfaces for a given VLAN. This allows end hosts to use a consistent default gateway regardless of which leaf switch they are connected to, enabling optimal east-west traffic routing directly at the distribution layer.

A. Using unique IP addresses on each switch for the gateway is inefficient and characteristic of legacy designs using protocols like VRRP, which the EVPN anycast gateway model replaces.

C. This describes a centrally-routed bridging (CRB) model, where Layer 3 routing is handled by core or spine devices, not an edge-routed design.

D. IRB interfaces are fundamental to the ERB model as they provide the Layer 3 routing capability at the edge; they must be enabled and configured.

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1. Juniper Networks TechLibrary, Data Center Fabric Architecture and Design Guide. In the "Edge-Routed Bridging Overlay" section, it states, "In an ERB overlay, the leaf devices function as both Layer 2 and Layer 3 gateways... To enable a host to move from one leaf device to another in the same VLAN and maintain its existing default gateway IP address, you can configure all leaf devices with the same IP address for the IRB interface... This feature is known as a default gateway or anycast gateway." (Reference: Data Center Fabric Architecture and Design Guide, Chapter: EVPN-VXLAN Fabric Architectures, Section: Edge-Routed Bridging Overlay).

2. Juniper Networks TechLibrary, EVPN-VXLAN Campus Architecture Guide. In the section "Edge-Routed Bridging Overlay Design," it explains, "In an ERB overlay, the access switches function as Layer 2 and Layer 3 gateways... All of the access switches in the EVPN-VXLAN fabric are configured with the same virtual gateway IP address and MAC address, which enables any of the access switches to act as the default gateway." (Reference: EVPN-VXLAN Campus Architecture Guide, Section: Edge-Routed Bridging Overlay Design).

3. Juniper Networks TechLibrary, Understanding EVPN with VXLAN Data Plane Encapsulation. Under the section "Symmetric and Asymmetric Integrated Routing and Bridging," the symmetric IRB model (which corresponds to ERB) is described as having IRB interfaces on all VTEPs (leaf switches) that need to perform routing. It highlights the use of a common gateway IP address across these VTEPs. (Reference: Junos OS EVPN User Guide, Section: Understanding EVPN with VXLAN Data Plane Encapsulation).

The use-cache option configures the switch to consult its local authentication cache when RADIUS servers are unreachable. This cache contains session information for supplicants that have previously authenticated successfully. Therefore, devices that are already authorized and have an entry in the cache will be permitted to maintain their access. New devices attempting to connect will not have an entry in the cache, and since the RADIUS server is unavailable to perform a new authentication, they will be denied access. This behavior precisely fulfills the stated requirements.

A. deny: This option blocks all supplicants, including those who were previously authorized, when the RADIUS server is unavailable.

B. vlan-name: This option moves all supplicants to a specified fallback VLAN, altering their network access rather than maintaining their current authorized state.

C. permit: This option allows all supplicants to access the network without authentication, which fails the requirement to deny new access attempts.

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1. Juniper Networks TechLibrary, "Understanding 802.1X Server Fail Fallback": This document details the behavior of the server-fail statement. It explicitly states for the use-cache option: "If the RADIUS servers are unavailable, the switch looks up the supplicant in its local authentication cache... If the supplicant is found in the cache, it is reauthenticated. If the supplicant is not found in the cache, it is denied access to the LAN." This directly supports the correct answer.

2. Juniper Networks TechLibrary, "Configuring 802.1X Server Fail Fallback (CLI Procedure)": This configuration guide describes the server-fail options. Under the use-cache description, it confirms that previously authenticated supplicants found in the cache are reauthenticated, while those not in the cache are denied access, aligning with the scenario's requirements.

The problem described is a direct result of exceeding the VSTP (VLAN Spanning Tree Protocol) instance limit on the switching platform. On many Juniper Networks EX Series switches, particularly those not using Enhanced Layer 2 Software (ELS), VSTP supports a maximum of 253 VLANs. With 450 VLANs configured, the system will only run a spanning-tree instance on the first 253 VLANs, leaving the remaining VLANs unprotected from Layer 2 loops. This causes the unprotected VLANs to "not function properly."

Enabling RSTP (Rapid Spanning Tree Protocol) resolves this scaling issue. RSTP operates as a single-instance protocol, creating one common spanning tree (CST) for all 450 VLANs, thus ensuring loop prevention across the entire network.

A. The force-version stp statement is used for interoperability with legacy devices running 802.1D-based PVST; it does not increase the VSTP instance limit.

C. The max-age parameter is an STP timer. Modifying it affects convergence time but has no impact on the number of VLANs the protocol can support.

D. The bridge priority value is used to influence the root bridge election process and does not affect the platform's VLAN scale limitations for VSTP.

1. Juniper Networks TechLibrary, "Understanding VSTP": This document specifies the platform-dependent limitations of VSTP. It states, "On EX Series switches that do not use the Enhanced Layer 2 Software (ELS) configuration style, VSTP supports a maximum of 253 VLANs. On EX Series switches that use ELS, VSTP supports a maximum of 509 VLANs." This directly supports the analysis that 450 VLANs exceeds the limit on non-ELS platforms.

2. Juniper Networks TechLibrary, "Spanning-Tree Protocol Overview": This document contrasts the different STP versions. It describes RSTP (IEEE 802.1w) as providing a single spanning tree for all VLANs, which confirms it as a solution for overcoming per-VLAN instance limits. It also notes, "If you have a large number of VLANs, we recommend MSTP instead of VSTP," further highlighting the known scaling issue with VSTP.

3. Juniper Networks TechLibrary, CLI Explorer, force-version (Protocols VSTP): The official documentation for this command states its purpose: "Force VSTP protocol compatibility with STP. VSTP is compatible with the PVST+ protocol. To enable VSTP to be compatible with the STP protocol, you must force the version of VSTP to be STP-compatible." This confirms the command is for compatibility, not for scaling.

The LOCALPREFERENCE BGP attribute is used to influence outbound traffic path selection within an Autonomous System (AS). The BGP path selection algorithm prefers the path with the highest LOCALPREFERENCE value. By default, Junos OS assigns a LOCALPREFERENCE of 100 to routes learned from BGP peers.

To make ISP A the preferred path, the route learned from ISP A must have a higher LOCALPREFERENCE than the route from ISP B. This can be achieved in two ways:

1. Increase the LOCALPREFERENCE for the route from ISP A to a value greater than 100.

2. Decrease the LOCALPREFERENCE for the route from ISP B to a value less than 100.

A. Assigning a lower local preference to the ISP A route would make it less preferred, causing traffic to be sent via ISP B.

D. Assigning a higher local preference to the ISP B route would make ISP B the preferred path, which is the opposite of the requirement.

1. Juniper Networks TechLibrary, Junos OS Routing Protocols Library for Routing Devices, BGP Path Selection.

Reference: In the "BGP Path Selection" section, step 2 of the algorithm states: "Prefer the path with the highest local preference." This confirms that a higher value is preferred. The document also notes the default value is 100.

Source: Junos OS BGP Path Selection

2. Juniper Networks, JNCIP-SP Study Guide, Chapter 3: BGP.

Reference: The section "The BGP Decision Process" explicitly details the path selection steps. It states, "The second step in the BGP decision process is to prefer the path with the highest local preference value. The local preference attribute is a well-known discretionary attribute that is used to influence BGP path selection for outbound traffic." This directly supports using local preference to control outbound traffic and favoring the highest value.

3. Juniper Networks TechLibrary, Junos OS Routing Protocols Library for Routing Devices, Example: Configuring BGP Local Preference.

Reference: This configuration example demonstrates applying a routing policy to an IBGP group to set the local preference. The example policy set-lp-200 uses the action then local-preference 200; to increase the preference, making a specific path more desirable. This validates the method described in the correct answers.

Source: Example: Configuring BGP Local Preference