JN0-664 Exam Dumps - Service Provider Professional (JNCIP-SP)

In the exhibit, we see two VRF (Virtual Routing and Forwarding) instances, CE-1 and CE-2, configured on a Juniper router. Each VRF is associated with a route-distinguisher (RD) and a vrf-target value.

Understanding the Role of vrf-target

The vrf-target is used to define Route Targets (RT), which control the import and export of VPN routes in MPLS Layer 3 VPNs (L3VPNs).

If two VRFs share the same RT, they will import each other's routes, allowing communication between them.

In this case, both VRFs have the same vrf-target:

vrf-target target:65512:100;

Since both CE-1 and CE-2 have the same RT (65512:100), they will import and export each other’s routes, enabling route sharing between them.

Understanding route-distinguisher (RD)

The RD (Route Distinguisher) only ensures uniqueness of overlapping IP prefixes within the MPLS network.

It does not control route sharing between VRFs.

In the exhibit, both VRFs have the same RD (65512:1), but this does not influence whether they share routes.

Correct Answer Selection

A (Correct): The vrf-target configuration enables route sharing between CE-1 and CE-2 since they have the same RT (65512:100).

B (Incorrect): The vrf-target does the opposite—it allows sharing, not blocking.

C (Incorrect): The route-distinguisher only provides unique route identification, but does not affect route sharing.

D (Incorrect): Again, route-distinguisher has no impact on route sharing.

Reference from Juniper Official Documentation

✅ Juniper Documentation - Junos MPLS VPNs Configuration Guide:

"Route targets (vrf-target) are used to control the import and export of VPN routes between different VRFs. VRFs with the same route target can import and export routes to each other, enabling inter-VRF communication."

Thus, the correct answer is:

✅ A. The vrf-target configuration will allow routes to be shared between CE-1 and CE-2.

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."

https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/topic-map/load-balancing-bgp-session.html

The resolve-vpn parameter is a BGP option that allows a router to resolve labeled VPN-IPv4 routes using unlabeled IPv4 routes received from another BGP peer with family inet labeled-unicast configured. This option enables interprovider VPNs without requiring MPLS labels between ASBRs or using VRF tables on ASBRs. In this scenario, you need to configure the resolve-vpn parameter under [edit protocols bgp group external family inet labeled-unicast] hierarchy level on both ASBRs.

Layer 2 VPNs don’t support fragmentation in the provider network. It is critical that the provider network supports the largest frame that the CE devices can generate after the MPLS and virtual routing and forwarding (VRF) labels are added by the PE devices. This example leaves the CE devices at the default 1500-byte maximum transmission unit (MTU) while configuring the provider core to support a 4000 byte MTU. This configuration avoids discards by ensuring the CE devices cannot exceed the MTU in the provider’s network.