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

Analyzing the Exhibit and Understanding the Issue

The exhibit shows BGP configurations on CE-1 and PE-1, which are connected via EBGP.

CE-1 (Customer Edge)

Uses AS 64511 and establishes an EBGP session with PE-1 (AS 65550).

Configured to export 10 static routes (192.168.1.0/24 - 192.168.10.0/24) using the static-to-bgp policy.

PE-1 (Provider Edge)

Uses AS 65550 and is peering with CE-1 (AS 64511).

Configured with a prefix-limit of 5 on received routes from CE-1.

Teardown enabled, meaning if more than 5 prefixes are received, the BGP session is shut down.

Identifying the Problem

CE-1 is correctly configured with peer AS 65550, so Option B ("CE-1 is configured with an incorrect peer AS") is incorrect ❌.

CE-1 is advertising exactly 10 static routes (as per policy).

PE-1 has a prefix-limit maximum 5 with teardown enabled.

This means that when CE-1 advertises more than 5 prefixes, PE-1 shuts down the BGP session.

BGP moves to the "Active" state, indicating that the session has been disrupted and PE-1 is trying to re-establish the connection.

CE-1 is reachable since the session was initially established before the limit was exceeded, so Option D ("CE-1 is unreachable") is incorrect ❌.

CE-1 is not advertising its entire routing table, only the static prefixes listed in the policy, so Option A ("CE-1 is advertising its entire routing table") is incorrect ❌.

Correct Answer

✅ C. The prefix limit has been reached on PE-1

Verification from Juniper Documentation

Juniper BGP Prefix Limit Documentation confirms that exceeding the prefix limit with teardown causes the BGP session to go into "Active" state.

Juniper Troubleshooting Guide for BGP Peering Issues states that when a BGP session reaches the prefix limit and has teardown enabled, the session is terminated.

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.**

**References**:

- Juniper Networks Documentation on Interprovider VPNs: [Interprovider VPN

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