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Juniper JN0-664 Service Provider Routing and Switching, Professional Exam JNCIP-SP Exam Practice Test
Question 1
Refer to the exhibit.
Click the Exhibit hutton.
You are configuring an interprovider Option C Layer 3 VPN to connect two customer sites.
Referring to the exhibit, which three statements are correct? (Choose three.)
Answer : A, B, C
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
Question 2
You have an L2VPN connecting two CEs across a provider network. The CEs and provider network are configured with the default MTU setting. You use the ping command from one
CE to the other CE with a size of 1500 bytes.
In this scenario, which statement is correct when using the ping command?
Answer : B
Layer 2 VPNs don't support fragmentation in the provider network. It is critical that the provider network supports the largest frame that the CE devices can generate after the MPLS and virtual routing and forwarding (VRF) labels are added by the PE devices. This example leaves the CE devices at the default 1500-byte maximum transmission unit (MTU) while configuring the provider core to support a 4000 byte MTU. This configuration avoids discards by ensuring the CE devices cannot exceed the MTU in the provider's network.
Question 3
You have an L2VPN connecting two CEs across a provider network that runs OSPF. You have OSPF configured on both CEs.
Which two statements are correct in this scenario? (Choose two.)
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)
Question 4
Refer to the exhibit.
Click the Exhibit button.
PE-1 and PE-2 are configured with LDP-signaled pseudowires to provide connectivity between CE-1 and CE-2. You notice no connectivity exists between CE-1 and CE-2.
Referring to the exhibit, which two statements describe potential causes for this fault? (Choose two.)
Answer : A, B
In the provided exhibit, PE-1 and PE-2 are configured with LDP-signaled pseudowires to provide Layer 2 connectivity between CE-1 and CE-2. The issue is that there is no connectivity between CE-1 and CE-2. Let's analyze the potential causes for this fault.
1. **LDP-Signaled Pseudowire (L2 Circuit) Configuration**:
- Pseudowires in MPLS networks use LDP (Label Distribution Protocol) to signal the virtual circuit (VC) labels between PE routers.
- For successful connectivity, the VC ID (Virtual Circuit Identifier) and LSPs (Label Switched Paths) between the PE routers must be correctly configured and operational.
2. **Analysis of the Exhibit**:
- The output shows the status of the L2 circuit connection on PE-1.
- The status (St) for the interface is `rmt Dn`, which indicates that the remote site (PE-2) is down or unreachable.
3. **Potential Causes**:
- **A. The VC IDs are mismatched**:
- Correct. If the VC IDs configured on PE-1 and PE-2 do not match, the L2 circuit cannot be established. Mismatched VC IDs prevent the pseudowire from forming correctly.
- **B. There is no LSP configured from PE-1 to PE-2**:
- Correct. LSPs are required for MPLS forwarding. If there is no LSP from PE-1 to PE-2, the LDP session cannot establish a path for the pseudowire. This results in the pseudowire being down.
- **C. Interface ge-0/0/0 on PE-1 is down**:
- Incorrect. The interface status is shown as `Up`, meaning the physical interface is operational.
- **D. There is no LSP configured from PE-2 to PE-1**:
- While this might seem like a potential issue, the specific problem of the remote site being down (`rmt Dn`) typically relates more directly to the forward path from PE-1 to PE-2 (i.e., no LSP from PE-1 to PE-2). Hence, the more accurate immediate cause is covered in Option B.
**Conclusion**:
Given the analysis, the correct statements describing potential causes for the fault are:
**A. The VC IDs are mismatched.**
**B. There is no LSP configured from PE-1 to PE-2.**
**Reference**:
- Juniper Networks Documentation on L2 Circuits: [Configuring Layer 2 Circuits](https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/layer-2-circuits-configuring.html)
- MPLS Configuration Guide: [Juniper MPLS Configuration](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/mpls-overview.html)
Question 5
Which two statements are correct regarding the PIM DR in a PIM-SM domain? (Choose two.)
Answer : A, C
In PIM-SM (Protocol Independent Multicast - Sparse Mode), the Designated Router (DR) plays a crucial role in multicast forwarding. The DR is responsible for various tasks depending on whether it is connected to the source or the receiver. Let's analyze each statement regarding the PIM DR in a PIM-SM domain.
1. **Statement A: The source DR sends PIM register messages from the source network to the RP.**
- Correct. In PIM-SM, the DR on the source's local network is responsible for encapsulating multicast packets in PIM Register messages and sending them to the Rendezvous Point (RP). This process ensures that the RP is aware of active sources.
2. **Statement B: If the DR priorities match, the router with the lowest IP address is selected as the DR.**
- Incorrect. The correct rule is that if the DR priorities match, the router with the **highest** IP address is selected as the DR. The election process first compares priorities; if priorities are equal, the IP addresses are compared to select the DR.
3. **Statement C: The receiver DR sends PIM join and PIM prune messages from the receiver network toward the RP.**
- Correct. In PIM-SM, the DR on the receiver's local network sends PIM Join messages toward the RP to join the multicast distribution tree. Similarly, it sends PIM Prune messages to leave the tree when there are no interested receivers.
4. **Statement D: By default, PIM DR election is performed on point-to-point links.**
- Incorrect. By default, PIM DR election is performed on multi-access networks (e.g., Ethernet). On point-to-point links, there is no need for a DR election as there are only two routers involved.
**Conclusion**:
The correct statements regarding the PIM DR in a PIM-SM domain are:
**A. The source DR sends PIM register messages from the source network to the RP.**
**C. The receiver DR sends PIM join and PIM prune messages from the receiver network toward the RP.**
**Reference**:
- Juniper Networks Documentation on PIM-SM: [PIM-SM Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/pim-sparse-mode-overview.html)
- RFC 7761, Protocol Independent Multicast - Sparse Mode (PIM-SM): [RFC 7761](https://tools.ietf.org/html/rfc7761) which details the PIM-SM protocol, including DR roles and election procedures.
Question 6
Exhibit
Referring to the exhibit, which statement is correct?
Answer : C
The route distinguisher (RD) is a BGP attribute that is used to create unique VPN IPv4 prefixes for each VPN in an MPLS network. The RD is a 64-bit value that consists of two parts: an administrator field and an assigned number field. The administrator field can be an AS number or an IP address, and the assigned number field can be any arbitrary value chosen by the administrator. The RD is prepended to the IPv4 prefix to create a VPN IPv4 prefix that can be advertised across the MPLS network without causing any overlap or conflict with other VPNs. In this question, we have two PE routers (PE-1 and PE-2) that are connected to two CE devices (CE-1 and CE-2) respectively. PE-1 and PE-2 are configured with VRFs named Customer-A and Customer-B respectively.
Question 7
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