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

Answer : A, B

The output is from the show l2vpn connections command on a Juniper router. This command is used to verify the status of Layer 2 VPN (L2VPN) pseudowires between Provider Edge (PE) routers.

Breakdown of Key Information:

Instance: vpn-A

This is the L2VPN instance being monitored.

Connection Status (St)

The connection status is 'Up', meaning the pseudowire is operational.

Local Site: CE1-2 (2)

The PE router is attached to a single local site (CE1-2).

Uptime & Connection Flaps

The output shows the last time the connection was up:

Time last up: Apr 11 14:35:27 2020

The '# Up trans' value is 1, meaning this connection has been established once and has not flapped since it was initiated.

VLAN ID Mismatch Check

The legend includes 'VM -- VLAN ID mismatch', but this status is not present in the connection output.

This means there is NO VLAN ID mismatch.

Flow Labels

The Flow Label Transmit is No, and the Flow Label Receive is No.

This means the PE router does NOT have the capability to pop flow labels.

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.

Answer : C

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.

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 : A

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.

Answer : A, C, E

To reduce the impact of suboptimal routing in OSPF and OSPFv3 after devices reboot, you can use the overload feature to prevent a router from being used as a transit router for a specified period of time. This allows the router to stabilize its routing table before forwarding traffic for other routers. To enable the overload feature, you need to do the following:

For OSPF, configure the overload statement under [edit protocols ospf] hierarchy level. You can also specify a timeout value in seconds to indicate how long the router should remain in overload state after it boots up. For example, set protocols ospf overload timeout 900 means that the router will be in overload state for 15 minutes after it boots up.

For OSPFv3, configure the overload statement under [edit protocols ospf3] hierarchy level. You can also specify a realm (ipv4-unicast or ipv6-unicast) and a timeout value in seconds to indicate how long the router should remain in overload state after it boots up for each realm. For example, set protocols ospf3 realm ipv4-unicast overload timeout 900 means that the router will be in overload state for 15 minutes after it boots up for IPv4 unicast routing.