Juniper JN0-637 Exam Questions

Comprehensive Detailed Step-by-Step Explanation with All Juniper Security Reference

Understanding the Problem:

A CoS-based VPN has been configured but is not functioning correctly.

The exhibit shows that under the class-of-service configuration, six forwarding classes are defined.

Forwarding Classes in the Exhibit:

best-effort

ef-class

af-class

network-control

res-class

web-data

Juniper CoS-Based VPN Limitations:

Maximum Number of Forwarding Classes: In CoS-based VPNs (Layer 3 VPNs), there is a limitation on the number of forwarding classes that can be used.

Supported Forwarding Classes: Only up to four forwarding classes are supported in an L3VPN for CoS purposes.

Additional Reference:

Juniper TechLibrary:

'Configuring Class of Service for MPLS VPNs' - Discusses CoS considerations and limitations in MPLS L3VPN deployments.

Source: Juniper TechLibrary - CoS for VPNs

Juniper Networks Day One Book:

'Deploying MPLS Layer 3 VPNs' - Provides insights into CoS limitations and best practices for VPN deployments.

Juniper Networks Documentation:

'For Layer 3 VPNs, the maximum number of forwarding classes supported is four. If you configure more than four forwarding classes, CoS functionality might not work as expected.'

Source: Juniper TechLibrary - Class of Service Limitations in VPNs

Issue Identification:

The VPN is not functioning correctly because it exceeds the maximum number of supported forwarding classes for a CoS-based VPN.

Solution:

Option D: You must delete one forwarding class.

By reducing the number of forwarding classes to four or fewer, the CoS-based VPN will comply with the limitations and function correctly.

Why Other Options Are Incorrect:

Option A: You must change the loss priorities of the forwarding classes to low.

Changing loss priorities does not affect the limitation on the number of forwarding classes.

The issue is not related to loss priority settings but to the number of forwarding classes.

Option B: You must change the code point for the DB-data forwarding class to 10000.

There is no forwarding class named DB-data in the exhibit.

Changing a code point does not address the issue of exceeding the maximum number of forwarding classes.

Option C: You must use inet precedence instead of DSCP.

Switching from DSCP to IP Precedence does not resolve the issue of having too many forwarding classes.

The limitation on the number of forwarding classes remains the same regardless of the classification method used.

Conclusion:

To resolve the issue with the CoS-based VPN not functioning correctly due to exceeding the maximum number of forwarding classes, you must delete forwarding classes to reduce the total number to four or fewer.

Comprehensive Detailed Step-by-Step Explanation with All Juniper Security Reference

Understanding the Scenario:

Multinode HA Default Mode Deployment:

In a chassis cluster, two SRX devices operate together to provide high availability.

ICL (Inter-Cluster Link) is Down:

The control and fabric links between the nodes are not operational.

Objective:

Determine how the SRX devices verify each other's activeness without the ICL.

Option A: Custom IP addresses may be configured for the activeness probe.

When the control link is down, SRX devices use an ICMP ping-based activeness probe to check the peer's status.

Custom IP addresses can be configured as probe targets to verify the peer's activeness.

'You can configure the SRX Series device to send activeness probes to a configured IP address to verify the peer's state when the control link is down.'

Source: Juniper Networks Documentation - Control Link Failure Detection

Option D: Each peer sends a probe with the virtual IP address as the source IP address and the upstream router as the destination IP address.

The SRX devices send ICMP probes to an upstream device using the redundancy group's virtual IP address as the source.

This helps determine if the peer node is still active by verifying network reachability.

'When the control link fails, each node sends ICMP pings to the configured probe addresses using the redundancy group's virtual IP address as the source.'

Source: Juniper Networks Documentation - Chassis Cluster Control Link Failure

Why Options B and C are Incorrect:

Option B: Fabric link heartbeats cannot be used because the ICL (which includes the fabric link) is down.

Option C: Probes are sent to upstream devices, not using the virtual IP address as the destination.

Conclusion:

The correct options are A and D because they accurately describe how SRX devices verify activeness without the ICL.