JN0-683 Sample Questions Answers

Telemetry Methods in Junos:

Telemetry is used to collect and report data from network devices. For high-frequency statistics reporting, such as every five seconds, you need a telemetry method that supports this level of granularity and real-time monitoring.

Junos Native Sensors:

Option C:Native Sensors in Junos provide detailed, high-frequency telemetry data, including TX and RX traffic statistics for interfaces. They are designed to offer real-time monitoring with customizable sampling intervals, making them ideal for the five-second reporting requirement.

Conclusion:

Option C:Correct—Native Sensors in Junos are capable of providing the required high-frequency telemetry data every five seconds.

 EVPN-VXLAN Configuration:

The configuration provided in the exhibit shows an EVPN-VXLAN setup where IP prefix routes are exchanged between two sites. The advertise direct-nexthop option and the VNI (Virtual Network Identifier) settings are crucial in this context.

 Advertise Direct-Nexthop:

Option A:The advertise direct-nexthop option ensures that the next-hop route is resolved using only the information carried in the EVPN Type 5 route. Type 5 routes are used for IP prefix advertisement in EVPN, which is key to enabling Layer 3 interconnectivity between different VXLAN segments.

 VNI Consistency:

Option C:For the same customer across different devices, the VNI must be consistent. This consistency ensures that all devices can correctly map traffic to the appropriate VXLAN segment, maintaining seamless Layer 2 and Layer 3 connectivity.

Telemetry in Data Centers:

Telemetry allows for real-time monitoring of network devices by collecting and exporting data such as interface statistics, routing table updates, and other key metrics.

Vendor-Neutral Data Models:

Option A:JTI (Junos Telemetry Interface) OpenConfig sensors use a vendor-neutral data model, which is important for ensuring compatibility across different network devices and systems. OpenConfig is an industry-standard model, which facilitates integration with various telemetry collection systems.

Conclusion:

Option A:Correct—OpenConfig sensors provide a vendor-neutral solution for telemetry, ensuring broad compatibility and flexibility in data center environments.

In the provided network configuration, Host A is in VLAN 100 and Host B is in VLAN 200. The issue arises because these two hosts are unable to communicate, which indicates that either the interfaces are not properly linked to their respective VLANs, or there is a missing static route required for inter-VLAN routing.

Step-by-Step Analysis:

VLAN Assignment:

The exhibit shows that irb.200 is correctly associated with VLAN 200 in the configuration. However, there is no corresponding irb.100 for VLAN 100. Without irb.100, the network lacks the logical interface to handle routing for VLAN 100. Thus, adding irb.100 to VLAN 100 is necessary.

Command to solve this:

set vlans vn100 13-interface irb.100

Static Route Configuration:

For inter-VLAN routing to occur, a static route needs to be configured that allows traffic to pass between different subnets (in this case, between VLAN 100 and VLAN 200). The command set routing-options static route 0.0.0.0/0 next-hop 192.168.200.10 would add a static route that directs all traffic from VLAN 100 to the correct gateway (192.168.200.10), which is necessary to route traffic between the two VLANs.

Command to solve this:

set routing-options static route 0.0.0.0/0 next-hop 192.168.200.10

Explanation of Incorrect Options:

Option A (delete vlans vn200 13-interface irb.200): This would remove the logical interface associated with VLAN 200, which is not desired because we need VLAN 200 to remain active and properly routed.

Option B (set interfaces irb unit 100 family inet address 192-168.100.1): This command would incorrectly assign an IP address that does not correspond with the subnet of VLAN 100 (192.168.200.1/24). This could create a misconfiguration, leading to routing issues.

Data Center References:

For a Data Center, proper VLAN management and static routing are crucial for ensuring that different network segments can communicate effectively, especially when dealing with separated subnets or zones like in different VLANs. This aligns with best practices in DCIM (Data Center Infrastructure Management) which stress the importance of proper network configuration to avoid downtime and ensure seamless communication between all critical IT infrastructure components.

Ensuring that the correct interfaces are associated with the correct VLANs and having the proper static routes in place are both essential steps in maintaining a robust and reliable data center network.

This detailed analysis reflects best practices as noted in standard data center design and network configuration guides​.

Understanding Pure IP Fabric:

A pure IP fabric is a network design where all devices operate at Layer 3, meaning that each device in the fabric is a router that makes forwarding decisions based on IP addresses.

Layer 2 Support:

In a pure IP fabric, traditional Layer 2 protocols such as Spanning Tree Protocol (STP) or VLANs are not supported. Instead, the network relies entirely on Layer 3 routing protocols to manage traffic between devices.

Routing Functionality:

Since devices in an IP fabric operate as Layer 3 routers, they handle IP routing and provide network services based on IP addresses, not on MAC addresses or Layer 2 switching.

Conclusion:

Option A:Correct—Devices in an IP fabric function as Layer 3 routers.

Option D:Correct—A pure IP fabric does not support traditional Layer 2 protocols, making it a purely routed environment.

Step 1: Understand the Configuration in the Exhibit

The exhibit provides three configuration snippets from a leaf device (user@leaf#):

Policy Options:

user@leaf# show policy-options

policy-statement load-balance {

term 1 {

then {

load-balance per-packet;

}

}

}

A policy named load-balance is defined, which applies the load-balance per-packet action. In Juniper terminology, per-packet actually means per-flow load balancing (a common point of confusion). This policy is intended to enable load balancing across multiple paths.

Routing Options:

user@leaf# show routing-options

router-id 192.168.100.11;

autonomous-system 65100;

The router ID is set to 192.168.100.11, and the autonomous system (AS) number is 65100. There’s no mention of applying the load-balance policy here, which is a clue to the issue.

BGP Configuration:

user@leaf# show protocols

bgp {

group spine {

type external;

export direct;

local-as 65003;

multipath {

multiple-as;

}

neighbor 172.16.1.5 {

peer-as 65001;

}

neighbor 172.16.1.17 {

peer-as 65002;

}

}

}

BGP is configured with an external group spine, where the leaf device (local AS 65003) peers with spine devices (AS 65001 and 65002).

The multipath multiple-as statement is enabled, which allows BGP to install multiple paths for the same prefix in the routing table, even if the paths come from different AS numbers. This is a prerequisite for load balancing in a multi-AS environment like an IP fabric.

The export direct policy is applied, which likely exports directly connected routes to the spine devices.

Step 2: Identify the Problem

The issue is that traffic from the leaf to the spine devices is not being load-balanced, despite the presence of a load-balance policy and BGP multipath. For load balancing to work in this scenario:

BGP multipath ensures multiple paths are installed in the routing table.

The load-balance per-packet policy is meant to distribute traffic across those paths.

However, the load-balance policy is defined but not applied anywhere in the configuration shown. For load balancing to take effect, the policy must be applied in the correct context.

Step 3: Evaluate the Options

Let’s go through each option to determine the correct solution:

A. The load-balance policy must be applied to the forwarding table under the routing-options hierarchy.

In Junos, to enable load balancing across multiple paths for forwarding, the load-balance policy must be applied at the forwarding table level. This is done under the routing-options hierarchy using the forwarding-table export statement. For example:

set routing-options forwarding-table export load-balance

This ensures that the load-balancing policy is applied to the forwarding table, allowing traffic to be distributed across multiple equal-cost paths installed by BGP.

B. The multipath multiple-as configuration must be configured for each peer in the BGP spine group.

The multipath multiple-as statement is already configured under the spine group, and it applies to all neighbors in that group (172.16.1.5 and 172.16.1.17). There’s no need to configure it per peer, as the group-level configuration is sufficient. This option is incorrect because the required setting is already in place.

C. The load-balance policy must be applied as an export policy to your BGP.

Applying the load-balance policy as a BGP export policy (e.g., export load-balance under the BGP group) would affect the routes advertised to the spine devices. However, the load-balance per-packet action is a forwarding action, not a route advertisement action. Applying it as a BGP export policy would not achieve the desired load balancing for traffic forwarding and is incorrect.

D. The load-balance policy must have a from statement that matches on protocol bgp.

The load-balance policy currently applies the load-balance per-packet action unconditionally (no from statement). Adding a from protocol bgp condition would make the policy apply only to BGP routes, but this is unnecessary in this context. The policy needs to be applied to the forwarding table to affect traffic, not modified with a from statement. This option doesn’t address the core issue of applying the policy.

Step 4: Determine the Correct Answer

The key issue is that the load-balance policy is defined but not applied. For load balancing to work, it must be applied to the forwarding table under routing-options. This matchesOption A:

A. The load-balance policy must be applied to the forwarding table under the routing-options hierarchy.

Step 5: Provide Official Juniper Documentation Reference

Since I don’t have direct access to Juniper’s proprietary documents, I can provide an explanation based on standard Junos documentation practices and publicly available resources, such as the Juniper TechLibrary, which is the official source for Junos configuration guides.

In Juniper’s official documentation, specifically in theJunos OS Routing Protocols and Policies Configuration Guide, the process for enabling load balancing is described as follows:

Load Balancing in Junos: To enable per-flow load balancing across multiple paths, you must define a policy with the load-balance per-packet action and apply it to the forwarding table. The relevant configuration hierarchy is:

routing-options {

forwarding-table {

export ;

}

}

Explanation from Documentation: The load-balance per-packet action (which performs per-flow balancing) requires the policy to be applied at the forwarding-table level to influence how traffic is distributed across multiple paths in the forwarding table. Without this, even if BGP installs multiple paths (via multipath), the forwarding engine will not load-balance traffic.

This aligns with the JNCIP-DC exam objectives, which include understanding how to configure and troubleshoot load balancing in an IP fabric, such as applying policies for traffic distribution.

Controlling Traffic Within a Tenant's Network:

The requirement is to limit access to specific traffic types within a tenant’s network without routing all tenant traffic through a firewall. This requires a selective method that can direct specific types of traffic to different paths based on the nature of the traffic.

Filter-Based Forwarding (FBF):

FBF is a technique that allows for routing decisions based on filters applied to the traffic, such as matching on source IP addresses, destination IP addresses, or even specific application types (like HTTP or FTP). This allows specific types of traffic to be forwarded to a specific next hop (e.g., a firewall) without affecting the entire traffic flow within the tenant's network.

Conclusion:

Option B:Correct—Filter-based forwarding allows for granular control of traffic, ensuring that only specific types of traffic within the tenant's network are redirected through a firewall, satisfying the requirement.

Understanding DCI (Data Center Interconnect) Schemes:

DCI schemes are used to connect multiple data centers, enabling seamless communication and resource sharing between them. The choice of DCI depends on the specific requirements, such as isolation, VNI translation, or routing domain separation.

VXLAN Stitching:

VXLAN stitching involves connecting multiple VXLAN segments, allowing VNIs (VXLAN Network Identifiers) from different segments to communicate with each other while maintaining separate routing domains.

This approach is particularly effective for keeping routing domains isolated while supporting VNI translation, making it ideal for scenarios where you need to connect different data centers or networks without merging their control planes.

Other Options:

A. MPLS DCI label exchange:This option typically focuses on MPLS-based interconnections and does not inherently support VNI translation or isolation in the context of VXLAN.

B. Over the top (OTT) with VNI translation enabled:This could support VNI translation but does not inherently ensure routing domain isolation.

D. Over the top (OTT) with proxy gateways:This typically involves using external gateways for traffic routing and may not directly support VNI translation or isolation in the same way as VXLAN stitching.

Data Center References:

VXLAN stitching is a powerful method in multi-data center environments, allowing for flexibility in connecting various VXLAN segments while preserving network isolation and supporting complex interconnect requirements.

Understanding Oversubscription in a Clos Fabric:

The oversubscription ratio in a Clos IP fabric measures the ratio of the amount of edge (leaf) bandwidth to the core (spine) bandwidth. An oversubscription ratio of 3:1 means that there is three times more edge bandwidth compared to core bandwidth.

Impact of Adding/Removing Spine Devices:

Option C:If youremove spine devices, the total available core bandwidth decreases, while the edge bandwidth remains the same. This results in anincrease in the oversubscription ratiobecause there is now less core bandwidth to handle the same amount of edge traffic.

Option B:Conversely, if youadd spine devices, the total core bandwidth increases. This decreases the oversubscription ratio because more core bandwidth is available to handle the edge traffic.

Conclusion:

Option C:Correct—Removing spine devices increases the oversubscription ratio.

Option B:Correct—Adding spine devices decreases the oversubscription ratio.

Junos Telemetry Interface (JTI):

The Junos Telemetry Interface is a framework that allows network operators to collect real-time telemetry data from Juniper devices. This data can be used for monitoring, analytics, and network automation.

Data Export Methods:

Option B:UDP (User Datagram Protocol)is a lightweight, connectionless protocol used for exporting telemetry data quickly with minimal overhead. While it doesn't guarantee delivery, it is suitable for high-speed data transfer where occasional packet loss is acceptable.

Option D:gRPC (gRPC Remote Procedure Call)is a modern, high-performance method for data export that supports streaming and remote procedure calls, making it ideal for more complex telemetry data use cases.

Conclusion:

Option B:Correct—UDP is supported for exporting telemetry data.

Option D:Correct—gRPC is also supported, offering advanced streaming capabilities

MAC Move Limiting:

MAC move limiting is a security feature used in network switches to detect and mitigate rapid changes in MAC address locations, which could indicate a network issue or an attack such as MAC flapping or spoofing.

When a MAC address is learned on a different interface than it was previously learned, the switch can take various actions to prevent potential issues.

Available Actions:

A. drop:This action drops packets from the MAC address if it violates the move limit, effectively blocking communication from the offending MAC address.

D. log:This action logs the MAC move event without disrupting traffic, allowing network administrators to monitor and investigate the event.

E. shutdown:This action shuts down the interface on which the MAC address violation occurred, effectively stopping all traffic on that interface to prevent further issues.

Other Actions (Not Correct):

B. filter:Filtering is not typically associated with MAC move limiting; it generally refers to applying ACLs or other mechanisms to filter traffic.

C. enable:This is not an action related to MAC move limiting, as it does not represent a specific reaction to a MAC move event.

Data Center References:

MAC move limiting is crucial for maintaining network stability and security, particularly in environments with dynamic or large-scale Layer 2 networks where MAC addresses might frequently change locations.

Collapsed Fabric Architecture:

A collapsed fabric refers to a simplified architecture where the spine and leaf roles are combined, often reducing the number of devices and links required.

In this architecture, the spine typically handles core switching, while leaf switches handle both access and distribution roles.

Understanding Border Gateway Functionality:

Border gateway functions include connecting the data center to external networks or other data centers.

In a collapsed fabric, these functions are usually handled at the leaf level, particularly on border leaf devices that manage the ingress and egress of traffic to and from the data center fabric.

Correct Statement:

D. Border gateway functions occur on border leaf devices:This is accurate in collapsed fabric architectures, where the border leaf devices take on the role of managing external connections and handling routes to other data centers or the internet.

Data Center References:

The collapsed fabric model is advantageous in smaller deployments or scenarios where simplicity and cost-effectiveness are prioritized. It reduces complexity by consolidating functions into fewer devices, and the border leaf handles the critical task of interfacing with external networks.

In conclusion, border gateway functions are effectively managed at the leaf layer in collapsed fabric architectures, ensuring that the data center can communicate with external networks seamlessly.

Understanding Network Architectures:

ERB (Edge Routed Bridging) architecture involves routing at the network's edge (leaf nodes), while traffic between leaf nodes is switched. This is commonly used in VXLAN-EVPN setups.

Analysis of the Exhibit:

The exhibit shows configurations related to routing instances, VXLAN, and VLANs, with VNIs being used for each VLAN. This setup is characteristic of an ERB architecture where each leaf device handles Layer 3 routing for its connected devices.

Conclusion:

Option B:Correct—The configuration shown corresponds to an ERB architecture where routing occurs at the network's edge (leaf devices).

VXLAN Traffic Verification:

To ensure VXLAN traffic from the xe-0/0/12 interface is correctly encapsulated by the logical vtep.32770 and sent to a remote leaf device, it is essential to monitor the relevant interface statistics.

The command show interfaces terse vtep.32770 statistics provides a concise overview of the traffic statistics for the specific VTEP interface, which can help verify whether traffic is being correctly encapsulated and transmitted.

Explanation:

This command is particularly useful for quickly checking the traffic counters and identifying any potential issues with VXLAN encapsulation or transmission.

It allows you to confirm that traffic is flowing as expected, by checking the transmitted and received packet counters.

Data Center References:

Monitoring interface statistics is a crucial step in troubleshooting and validating network traffic, particularly in complex overlay environments like EVPN-VXLAN.

VXLAN Group-Based Policies (GBP):

VXLAN Group-Based Policies are used to apply security policies consistently across the network. These policies are often tied to user or device identities rather than static IP addresses, which allows for more dynamic and scalable security management.

Scalable Group Tags via RADIUS and 802.1X:

Option B:VXLAN GBP can use scalable group tags configured on a RADIUS server, which are then pushed to network devices through 802.1X. This allows for centralized and automated policy application based on user or device identity.

Consistent Security Policy Application:

Option C:GBP ensures that security policies are consistently applied across the network, regardless of where a user or device connects. This consistency is crucial in environments where security policies must follow the user or device.

Conclusion:

Option B:Correct—Group tags can be configured on a RADIUS server and pushed via 802.1X, enabling centralized policy management.

Option C:Correct—GBP ensures consistent application of security policies, which is essential for maintaining security across a dynamic network environment.