Juniper JN0-664 Dumps - Pass Service Provider Routing and Switching, Professional Exam in First Attempt 2026

A sham link is a logical link between two PE routers that belong to the same OSPF area but are connected through an L3VPN. A sham link makes the PE routers appear as if they are directly connected, and prevents OSPF from preferring an intra-area back door link over the VPN backbone.To create a sham link, you need to configure the local and remote addresses of the PE routers under the [edit protocols ospf area area-id] hierarchy level1.

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/configuring-ospfv2-sham-links.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.

https://www.juniper.net/documentation/us/en/software/nce/feature-guide-virtual-private-lan-service/topics/task/vpls-ldp-signaling-solutions.html

https://www.juniper.net/documentation/us/en/software/junos/vpn-l2/topics/concept/vpns-configuring-vpls-routing-instances.html#id-11510150__id-11568648

Option A (Correct):

Complete Sequence Number PDUs (CSNPs)are periodically flooded by theDesignated Intermediate System (DIS)on multi-access networks (e.g., Ethernet).

This ensures all routers on the segment synchronize theirLink-State Databases (LSDBs).

Option C (Correct):

Partial Sequence Number PDUs (PSNPs)containonly the headers (descriptions)of LSPs (e.g., LSP ID, sequence number, checksum).

PSNPs are used to:

Request missing LSPs(when a router detects discrepancies via CSNPs).

Acknowledge LSP receipt(in point-to-point networks).

They donotinclude the full LSP data.

Why Other Options Are Incorrect:

Option B:Incorrect. PSNPs arenot flooded periodically---they are senton-demandfor specific LSP synchronization.

Option D:Incorrect. While CSNPsdocontain LSP descriptions (headers), the term 'only' is misleading. CSNPssummarize all LSPsin the LSDB, but they are not limited to 'only' descriptions---they serve as a complete database overview.

Key Takeaways:

CSNPsareperiodic,broadcastby the DIS, and ensure LSDB consistency.

PSNPsaretriggered, containspecific LSP headers, and handle requests/acknowledgments.

IS-IS usesCSNPs and PSNPsto maintain efficient LSDB synchronization without flooding full LSPs unnecessarily.

For further details, refer to Juniper's official IS-IS documentation: Juniper IS-IS Configuration Guide.

Interprovider Option C for Layer 3 VPNs involves the use of Autonomous System Boundary Routers (ASBRs) to exchange labeled VPN-IPv4 routes between different Autonomous Systems (AS). This option requires BGP sessions between ASBRs, and the VPN routes are carried end-to-end using MPLS labels. Here's a detailed analysis of the roles of different routers in this scenario:

1. **ASBR Routers**:

- ASBRs are responsible for exchanging VPN-IPv4 routes between different ASes.

- **A. ASBR routers maintain the internal routes from its own AS and the loopback addresses from the other AS PEs.**

- Correct. ASBRs maintain routes to internal destinations within their own AS, and they also need to know the loopback addresses of PEs in the other AS to set up the BGP sessions and MPLS tunnels.

2. **PE Routers**:

- PE routers are responsible for maintaining VPN routes and label information to forward VPN traffic correctly.

- **B. PE routers maintain the internal routes from its own AS, the loopback address from the other AS PEs, and the L3VPN routes.**

- Correct. PE routers need to maintain:

- Internal routes within their AS for routing.

- Loopback addresses of other AS PEs for establishing MPLS LSPs.

- L3VPN routes to provide end-to-end VPN connectivity.

3. **P Routers**:

- P routers are the core routers that do not participate in BGP VPN routing but forward labeled packets based on MPLS labels.

- **C. P routers only maintain the internal routes from their own AS.**

- Correct. P routers maintain the internal routing information to forward packets within the AS and use MPLS labels for forwarding VPN packets. They do not maintain VPN routes or routes from other ASes.

4. **Incorrect Statements**:

- **D. P routers maintain the internal routes from its own AS and the loopback address from the other AS PEs.**

- Incorrect. P routers do not need to maintain the loopback addresses of other AS PEs. They only maintain internal routing and MPLS label information.

- **E. ASBR routers maintain the internal routes from its own AS, the loopback address from the other AS PEs, and the L3VPN routes.**

- Incorrect. ASBR routers do not maintain L3VPN routes. They exchange labeled VPN-IPv4 routes with other ASBRs and forward them to PE routers.

**Conclusion**:

The correct answers are:

**A. ASBR routers maintain the internal routes from its own AS and the loopback addresses from the other AS PEs.**

**B. PE routers maintain the internal routes from its own AS, the loopback address from the other AS PEs, and the L3VPN routes.**

**C. P routers only maintain the internal routes from their own AS.**

**Reference**:

- Juniper Networks Documentation on Interprovider VPNs: [Interprovider VPN Configuration](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/mpls-vpn-interprovider.html)

- MPLS and VPN Architectures, CCIP Edition by Ivan Pepelnjak and Jim Guichard