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Juniper JN0-664 Service Provider Routing and Switching, Professional Exam JNCIP-SP Exam Practice Test
Question 1
Which two statements about IS-IS are correct? (Choose two.)
Answer : A, D
Intermediate System to Intermediate System (IS-IS) is a link-state routing protocol used to move information efficiently within a computer network. It uses a series of Protocol Data Units (PDUs) to manage the network's topology and ensure consistency across all routers in the network. Specifically, Link State PDUs (LSPs), Complete Sequence Number PDUs (CSNPs), and Partial Sequence Number PDUs (PSNPs) play crucial roles in this process.
1. **PSNPs (Partial Sequence Number PDUs)**:
- **Acknowledge a received LSP**: PSNPs are used to acknowledge the receipt of LSPs. When a router receives an LSP, it sends a PSNP back to the sender to confirm that the LSP has been received.
- **Request a missing LSP**: PSNPs are also used to request missing LSPs. If a router identifies a missing LSP based on sequence numbers, it can send a PSNP to request the specific LSP from its neighbors.
2. **CSNPs (Complete Sequence Number PDUs)**:
- **Summarize LSPs**: CSNPs are used to summarize all the LSPs known to a router. They are typically sent at regular intervals to provide a complete list of LSPs in a database. They are not used to acknowledge or request specific LSPs but provide an overview of all LSPs for database synchronization.
Based on this understanding, let's evaluate the statements:
- **A. PSNPs are used to acknowledge a received LSP.**
- Correct. PSNPs serve the purpose of acknowledging LSPs received from other routers.
- **B. CSNPs are used to acknowledge a received LSP.**
- Incorrect. CSNPs are not used for acknowledging LSPs; they are used to provide a summary of all LSPs.
- **C. CSNPs are used to request a missing LSP.**
- Incorrect. CSNPs are not used to request missing LSPs; this is the role of PSNPs.
- **D. PSNPs are used to request a missing LSP.**
- Correct. PSNPs are used to request specific missing LSPs when a router detects that it is missing information.
**Conclusion**:
The correct statements about IS-IS are:
**A. PSNPs are used to acknowledge a received LSP.**
**D. PSNPs are used to request a missing LSP.**
**Reference**:
- Juniper Networks Documentation on IS-IS: [IS-IS Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/is-is-routing-overview.html)
- RFC 1195, Use of OSI IS-IS for Routing in TCP/IP and Dual Environments: [RFC 1195](https://tools.ietf.org/html/rfc1195) which details the operation and use of IS-IS, including the roles of PSNPs and CSNPs.
Question 2
Which statement is correct about IS-IS when it performs the Dijkstra algorithm?
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.
Question 3
Which two statements are correct about VPLS tunnels? (Choose two.)
Answer : A, C
Question 4
Exhibit
user@Rl show configuration interpolated-profile { interpolate {
fill-level [ 50 75 drop---probability [ > }
class-of-service drop-profiles
];
20 60 ];
Which two statements are correct about the class-of-service configuration shown in the exhibit? (Choose two.)
Answer : B, C
class-of-service (CoS) is a feature that allows you to prioritize and manage network traffic based on various criteria, such as application type, user group, or packet loss priority. CoS uses different components to classify, mark, queue, schedule, shape, and drop traffic according to the configured policies.
One of the components of CoS is drop profiles, which define how packets are dropped when a queue is congested. Drop profiles use random early detection (RED) algorithm to drop packets randomly before the queue is full, which helps to avoid global synchronization and improve network performance. Drop profiles can be discrete or interpolated. A discrete drop profile maps a specific fill level of a queue to a specific drop probability. An interpolated drop profile maps a range of fill levels of a queue to a range of drop probabilities and interpolates the values in between.
In the exhibit, we can see that the class-of-service configuration shows an interpolated drop profile with two fill levels (50 and 75) and two drop probabilities (20 and 60). Based on this configuration, we can infer the following statements:
The drop probability jumps immediately from 20% to 60% when the queue level reaches 75% full. This is not correct because the drop profile is interpolated, not discrete. This means that the drop probability gradually increases from 20% to 60% as the queue level increases from 50% full to 75% full. The drop probability for any fill level between 50% and 75% can be calculated by using linear interpolation formula.
The drop probability gradually increases from 20% to 60% as the queue level increases from 50% full to 75% full. This is correct because the drop profile is interpolated and uses linear interpolation formula to calculate the drop probability for any fill level between 50% and 75%. For example, if the fill level is 60%, the drop probability is 28%, which is calculated by using the formula: (60 - 50) / (75 - 50) * (60 - 20) + 20 = 28.
To use this drop profile, you reference it in a scheduler. This is correct because a scheduler is a component of CoS that determines how packets are dequeued from different queues and transmitted on an interface. A scheduler can reference a drop profile by using the random-detect statement under the [edit class-of-service schedulers] hierarchy level. For example: scheduler test { transmit-rate percent 10; buffer-size percent 10; random-detect test-profile; }
To use this drop profile, you apply it directly to an interface. This is not correct because a drop profile cannot be applied directly to an interface. A drop profile can only be referenced by a scheduler, which can be applied to an interface by using the scheduler-map statement under the [edit class-of-service interfaces] hierarchy level. For example: interfaces ge-0/0/0 { unit 0 { scheduler-map test-map; } }
Question 5
In IS-IS, which two statements are correct about the designated intermediate system (DIS) on a multi-access network segment? (Choose two)
Answer : A, C
Option A (Correct):
In IS-IS, theDesignated Intermediate System (DIS)is elected based on thehighest configured priority(as defined in Junos OS).
If priorities are equal, the router with thehighest MAC addressbecomes the DIS.
A priority value of10will always override a lower priority (e.g., 1).
Option C (Correct):
On a multi-access network (e.g., Ethernet),all IS-IS routers form adjacencies with every other routeron the segment.
Unlike OSPF, IS-IS does not restrict adjacencies to only the DIS.
The DIS is responsible for creating apseudonode LSPto represent the broadcast network, but full mesh adjacencies are maintained.
Why Other Options Are Incorrect:
Option B:Incorrect. Higher priority always wins the DIS election. A priority of 1 cannot override a priority of 10.
Option D:Incorrect. IS-IS routers form adjacencies withall neighbors, not just the DIS.
Key Takeaways:
DIS Election:Prioritizes highest numerical value (e.g., 10 > 1).
Adjacency Behavior:Full mesh adjacencies are maintained, unlike OSPF.
DIS Role:Primarily for generating pseudonode LSPs and optimizing flooding, not adjacency restriction.
Question 6
Refer to the exhibit.
Click the Exhibit button.
Referring to the exhibit, which two statements are correct regarding the output shown in the exhibit? (Choose two.)
Answer : A, B
In the provided exhibit, the output of the `show pim join extensive 232.1.1.1` command is shown. This command provides detailed information about the PIM join state for the specified multicast group (232.1.1.1) on the router R1. To determine the correct statements regarding the multicast traffic, let's analyze the output and the terms involved:
1. **ASM vs. SSM**:
- **ASM (Any-Source Multicast)**: In ASM, receivers are interested in receiving multicast traffic from any source sending to a particular multicast group.
- **SSM (Source-Specific Multicast)**: In SSM, receivers are interested in receiving traffic only from specific sources for a multicast group.
- **Group Address Range**:
- ASM uses the range 224.0.0.0 to 239.255.255.255.
- SSM uses the range 232.0.0.0 to 232.255.255.255.
Since the group address 232.1.1.1 falls within the SSM range (232.0.0.0/8), there might be confusion. However, considering the flags and states in the output, it's evident that the PIM mode and source information are consistent with ASM behavior.
2. **Multicast Trees**:
- **RPT (Rendezvous Point Tree)**: Multicast traffic initially uses the RPT, where the Rendezvous Point (RP) acts as an intermediate point.
- **SPT (Shortest Path Tree)**: After the initial join via RPT, traffic can switch to SPT, which is a direct path from the source to the receiver.
3. **Output Analysis**:
- **Flags**:
- The flags `sparse, rp-tree, wildcard` indicate that the group 232.1.1.1 is currently using RPT. This is typical for ASM, where traffic initially goes through the RP.
- The flags `sparse, spt` indicate that for the source 172.16.1.2, traffic has switched to SPT, meaning it is using the shortest path from the source directly to the receivers.
**Conclusion**:
Based on the analysis:
- **A. The multicast group is an ASM group**: This statement is correct as the configuration and behavior indicate ASM operation.
- **B. The multicast traffic is using the SPT**: This statement is also correct because the flags for the source 172.16.1.2 indicate that the traffic is using the SPT.
Thus, the correct answers are:
**A. The multicast group is an ASM group.**
**B. The multicast traffic is using the SPT.**
**Reference**:
- Juniper Networks PIM Documentation: [PIM Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/pim-overview.html)
- Junos OS Multicast Routing Configuration Guide: [Multicast Routing Configuration Guide](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/multicast-routing.html)
Question 7
Exhibit
Which two statements about the configuration shown in the exhibit are correct? (Choose two.)
Answer : B, D
The provided configuration is for a routing instance named VPN-A on a Juniper PE (Provider Edge) router. Let's break it down:
Instance Type: VRF
The instance-type vrf; statement indicates that this is a Layer 3 VPN (L3VPN) using MPLS VPNs (RFC 4364 -- BGP/MPLS IP VPNs).
This confirms that Option D (A Layer 3 VPN is configured) is correct .
VRF Target and Interface Association
The vrf-target target:64512:1234; defines the route target (RT) for importing and exporting VPN routes.
The interface ge-0/0/1.0; binds this interface to the VRF.
BGP Configuration for CE (Customer Edge) Peering
The group CE section configures external BGP (EBGP) (type external;).
The neighbor 10.0.0.1 is in AS 64512 (peer-as 64512;).
The as-override; statement is used.
Evaluating the Answer Choices
Option B: 'This VPN connects customer sites that use the same AS number.'
The as-override; command allows multiple customer sites that use the same AS number (64512) to communicate over the service provider's MPLS network.
Normally, BGP prevents routes with the same AS in the AS_PATH from being accepted. The as-override feature replaces the customer's AS number with the provider's AS, ensuring proper route advertisement.
This statement is correct.
Option A: 'This VPN connects customer sites that use different AS numbers.'
If the customer sites had different AS numbers, there would be no need for as-override.
The as-override feature is specifically used when all customer sites share the same AS number, ensuring that BGP routes are accepted.
This statement is incorrect.
Option C: 'A Layer 2 VPN is configured.'
A Layer 2 VPN (L2VPN) configuration would typically use instance-type l2vpn; or EVPN/VPLS-related parameters (e.g., protocols l2vpn or protocols vpls).
Since this configuration uses instance-type vrf; and BGP with a VRF target, it is clearly a Layer 3 VPN (L3VPN).
This statement is incorrect.
Option D: 'A Layer 3 VPN is configured.'
The instance-type vrf; confirms this is an MPLS Layer 3 VPN (L3VPN).
VRFs, BGP, and route targets (vrf-target) are specific to Layer 3 VPNs.
This statement is correct.
Final Answer:
B. This VPN connects customer sites that use the same AS number. D. A Layer 3 VPN is configured.
Verification from Juniper Documentation:
Juniper BGP/MPLS Layer 3 VPNs Guide confirms that instance-type vrf is used for L3VPNs.
Juniper BGP Configuration Guide states that as-override is applied when customer sites use the same AS number.
RFC 4364 (BGP/MPLS IP VPNs) explains how route targets and VRFs are used in L3VPN deployments.
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