Juniper Service Provider Routing and Switching, Professional Exam JN0-664 JNCIP-SP Exam Questions

Answer : D

The auto-export parameter is a routing option that allows a routing instance to share routes with other routing instances or the master routing table. The auto-export parameter automatically exports routes from one routing instance to another based on the route target communities attached to the routes. In this scenario, the 10.101.1.0/24 route will be shared if the auto-export parameter is configured under [edit routing-options] hierarchy level.

Answer : A

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/command/show-route-advertising-protocol.html

Answer : B, D

In an L2VPN scenario, the provider network connects two customer edge (CE) devices across a Layer 2 virtual private network. Let's analyze how OSPF operates in this setup.

1. **OSPF Neighborship in L2VPN**:

- An L2VPN provides a Layer 2 connection between two sites, making it transparent to Layer 3 protocols like OSPF. This means the CEs can form OSPF adjacencies directly with each other as if they were on the same local network.

2. **OSPF Configuration on CEs and PEs**:

- **Statement A: OSPF neighborship is formed between the CEs and PEs**:

- Incorrect. In an L2VPN, the provider's network is transparent to the OSPF running on the CEs. OSPF neighborship forms directly between the CEs, not between the CEs and PEs.

- **Statement B: The CE and PE OSPF areas can be different**:

- Correct. Since OSPF adjacencies form directly between the CEs and not between CEs and PEs, the OSPF areas on the CEs and PEs can be different. The provider network acts as a transparent bridge, and OSPF doesn't see the PEs.

- **Statement C: The CE and PE OSPF areas must match**:

- Incorrect. As noted above, because the OSPF neighborship forms directly between the CEs, the OSPF areas on the CEs and PEs do not need to match.

- **Statement D: OSPF neighborship is formed between the two CEs**:

- Correct. The L2VPN makes the connection between the two CEs appear as a direct Layer 2 link, allowing them to form an OSPF adjacency directly.

**Conclusion**:

Given the above analysis, the correct statements are:

**B. The CE and PE OSPF areas can be different.**

**D. OSPF neighborship is formed between the two CEs.**

**Reference**:

- Juniper Networks Documentation on L2VPNs: [Configuring Layer 2 VPNs](https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/layer-2-vpns-configuring.html)

- OSPF Configuration Guide: [Junos OS OSPF Configuration](https://www.juniper.net/documentation/en_US/junos/topics/concept/ospf-routing-overview.html)

Answer : A, B

The hello interval is the time interval between two consecutive hello packets sent by an OSPF router on an interface. The dead interval is the time interval after which a neighbor is declared down if no hello packets are received from it. These parameters must match between two OSPF routers for them to form an adjacency. In the exhibit, router R1 has a hello interval of 10 seconds and a dead interval of 40 seconds, while router R2 has a hello interval of 30 seconds and a dead interval of 120 seconds.This causes a mismatch and prevents them from becoming neighbors23.

Answer : B, D

Bootstrap messages are PIM messages that are used to distribute rendezvous point (RP) information dynamically during an RP election. Bootstrap messages are sent by bootstrap routers (BSRs), which are routers that are elected to perform the RP discovery function for a PIM sparse-mode domain. Bootstrap messages contain information about candidate RPs and their multicast groups, as well as BSR priority and hash mask length. Bootstrap messages are forwarded to all routers within a PIM sparse-mode domain using hop-by-hop flooding.

Answer : B

The Dijkstra algorithm in IS-IS operates as follows:

Tree Database Initialization: The local router (root) is added to the tree database with a cost of 0.

Candidate Database Population: Neighbors of the root (from the LSDB) are placed into the candidate database with their associated costs.

Processing Nodes: The node with the lowest cost in the candidate database is moved to the tree database.

Neighbor Evaluation: For each neighbor of the newly added node (from the LSDB), if the neighbor is not already in the tree or candidate database, it is added to the candidate database. If it exists in the candidate with a higher cost, it is updated with the lower cost.

Termination: The algorithm stops when thecandidate database is empty, ensuring all shortest paths are computed.

Analysis of Options:

A .Incorrect. The local router is placed directly into the tree database, not the candidate database.

B .Correct (with context). When a node is added to the tree database, its neighbors (existing in the LSDB) are evaluated. If these neighbors are not already in the tree or candidate database, they areadded(not 'moved') to the candidate database. The wording 'moved' is technically inaccurate, but this option aligns closest with the process of populating the candidate database using LSDB entries during tree database processing.

C .Incorrect. Tuples (nodes) with the lowest cost are moved from thecandidatedatabase to thetreedatabase, not from the tree to the LSDB. The LSDB remains static during SPF computation.

D .Incorrect. The algorithm stops when thecandidate database is empty, not the tree database. The tree database grows as nodes are processed.

Answer : C

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.