Juniper JN0-664 Exam Dumps - Actual Questions Answers

When a Juniper device receives a packet on an interface with both a Behavior Aggregate (BA) classifier and a Multifield (MF) classifier, Junos OS follows a specific processing order to apply Class of Service (CoS).

Understanding the Classifiers in Junos CoS

1️⃣ Behavior Aggregate (BA) Classifier

Uses packet headers (DSCP, IP precedence, or MPLS EXP bits) to classify traffic into forwarding classes.

Applied at the ingress interface.

Example: A packet with DSCP 46 (Expedited Forwarding) is mapped to a high-priority queue.

2️⃣ Multifield (MF) Classifier

Uses match conditions (like source/destination IP, port numbers, protocol types) to classify traffic.

Typically used for more granular classification beyond what BA can provide.

Junos Processing Order:

🔹 When both BA and MF classifiers are configured on an interface, Junos first applies the BA classifier, then the MF classifier.

🔹 MF classifier can override the BA classification if necessary.

Evaluating the Answer Choices

✅ B. The packet will be processed by the BA classifier first, then the MF classifier.

Correct, because Junos first applies BA classification based on DSCP/MPLS EXP bits.

After BA classification, the MF classifier is applied, which can refine or override the BA classification.

❌ A. The packet will be discarded.

Incorrect, because classification does not drop packets unless explicitly configured with a filter or policing action.

❌ C. The packet will be forwarded with no classification changes.

Incorrect, because both classifiers are applied in a specific order, meaning classification changes will occur.

❌ D. The packet will be processed by the MF classifier first, then the BA classifier.

Incorrect, because BA classification is always applied first, followed by MF classification.

Final Answer: ✅ B. The packet will be processed by the BA classifier first, then the MF classifier.

🔹 Official Juniper Reference:

"When both BA and MF classifiers are applied on an interface, Junos OS first classifies packets using the BA classifier before applying the MF classifier."

AToM (Any Transport over MPLS) is a framework that supports various Layer 2 transport types over an MPLS network core. One of the transport types supported by AToM is LDP Layer 2 circuit, which is a point-to-point Layer 2 connection that uses LDP for signaling and MPLS for forwarding. LDP Layer 2 circuit can support Layer 2 connectivity without using BGP and can be scalable and efficient by using a single MPLS LSP for multiple VPN connections. The customer can maintain all routing for their private network by using their own CE switches.

The issue arises because R3’s group-range (224.1.1.0/28) is more specific than R2’s group-range (224.1.1.0/24). In PIM bootstrap (BSR), the RP with the longest prefix (most specific group-range) is preferred, regardless of priority. Even though R3 has a higher bootstrap priority (210 vs. R2’s 200), its more specific /28 group-range takes precedence for groups within 224.1.1.0/28.

Why Option D is Correct:

To force R4 to use R2 for all joins, R2’s group-range must be more specific than R3’s. For example:

If R2’s group-range is changed to 224.1.1.0/28 (same as R3) but with a higher priority, R2 would win (priority is compared only when group-ranges are equal).

If R2’s group-range is changed to 224.1.1.0/29 (more specific than /28), it will override R3’s /28 for groups in the /29 range.

The key is prefix specificity, which overrides priority in BSR elections.

Why Other Options Are Incorrect:

A. Change bootstrap priority on R2 to be higher than R3:

Priority is evaluated only when group-ranges are identical. Since R3’s group-range (/28) is more specific than R2’s (/24), R3 will still win for groups in 224.1.1.0/28, even if R2’s priority is higher.

B. Change the default route in inet.2 on R4:

RPF routes (inet.2) determine how traffic reaches the RP, but they do not influence RP election logic (BSR priority/group-range).

C. Change R2’s local address to be higher than R3’s:

The RP address is a tiebreaker only if priorities and group-ranges are equal. Since R3’s group-range is more specific, this change has no impact.

Key Takeaways:

BSR RP Election Order:

Longest group prefix (most specific).

Highest priority (if prefixes are equal).

Highest RP address (if prefixes and priorities are equal).

To override R3, R2 must advertise a more specific group-range (e.g., /28 or smaller) to ensure it is selected for the desired multicast groups.