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

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.**

**References**:

- 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)

EVPN is a technology that connects L2 network segments separated by an L3 network using a virtual Layer 2 network overlay over the Layer 3 network. EVPN uses BGP as its control protocol to exchange different types of routes for different purposes. Type 2 routes are used to advertise MAC address and IP address pairs learned using ARP snooping from the local CE devices. Type 3 routes are used to join a multicast tree to flood traffic such as broadcast, unknown unicast, and multicast (BUM) traffic.

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.**

**References**:

- 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.

Route reflection is a BGP feature that allows a router to reflect routes learned from one IBGP peer to another IBGP peer, without requiring a full-mesh IBGP topology. Route reflectors do not change any existing BGP attributes by default when advertising routes, unless explicitly configured to do so. A BGP peer does not require any configuration changes to become a route reflector client, only the route reflector needs to be configured with the client parameter under [edit protocols bgp group group-name neighbor neighbor-address] hierarchy level.

In OSPF, routers form adjacencies by exchanging Hello packets. These packets contain several parameters that must match between OSPF neighbors to establish a successful adjacency. Key among these parameters are the Hello Interval and the Dead Interval.

Let's analyze the exhibit and the question to determine the correct course of action to ensure that R4 peers with both R1 and R2.

1. **OSPF Hello and Dead Intervals**:

- **Hello Interval**: The time in seconds between Hello packets sent out by a router. Default is usually 10 seconds for broadcast and point-to-point networks.

- **Dead Interval**: The time in seconds that a router will wait to receive a Hello packet from a neighbor before declaring the neighbor down. Default is usually four times the Hello Interval (40 seconds).

2. **Analysis of the Exhibit**:

- **R1's Interface**: Shows a Dead Interval of 40 seconds.

- **R2's Interface**: Shows a Dead Interval of 40 seconds.

- **R4's Interface**: Shows a Dead Interval of 20 seconds.

From the exhibit, we can see that R4 has a Dead Interval of 20 seconds, while R1 and R2 have Dead Intervals of 40 seconds. This discrepancy prevents R4 from establishing an OSPF peering with R1.

3. **Option Analysis**:

- **A. Adjust the Priority on R1 to be lower than the Priority on R4**:

- Incorrect. The OSPF Priority is used for DR/BDR election on multi-access networks and does not impact peering issues.

- **B. Change the MTU size on R1 and R2 to be 22 bytes higher than R4's MTU size**:

- Incorrect. While MTU mismatches can prevent OSPF adjacencies, the exhibit does not indicate an MTU mismatch issue.

- **C. Adjust the Dead Interval on R4 to match the Dead Interval on R1 and R2**:

- Correct. Matching the Dead Interval on R4 to 40 seconds will ensure that all routers have consistent Hello and Dead Intervals, allowing OSPF adjacencies to form.

- **D. Adjust the Hello Interval on R1 and R2 to match the Hello Interval on R4**:

- While this would be a valid approach if the Hello Intervals were mismatched, the exhibit shows that the Hello Intervals are consistent (10 seconds) across all routers. Therefore, this adjustment is not necessary.

**Conclusion**:

To correct the OSPF peering issue, the Dead Interval on R4 should be adjusted to match the Dead Intervals on R1 and R2. The correct answer is:

**C. Adjust the Dead Interval on R4 to match the Dead Interval on R1 and R2.**

**References**:

- Juniper Networks Documentation on OSPF: [OSPF Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/ospf-routing-overview.html)

- OSPF Configuration Guide: [Configuring OSPF](https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/ospf-configuring.html)

To create a summary route for IS-IS, you need to configure a policy statement that matches the prefixes to be summarized and sets the next-hop to discard. You also need to configure a summary-address statement under the IS-IS protocol hierarchy that references the policy statement. In this case, the policy statement leak-v6 is trying to match the prefix 2001:db9:a:fa00::/61 exactly, but this prefix is not advertised by any router in the network. Therefore, no summary route is created. To fix this, you need to delete the longer keyword from the route-filter term and change the prefix length to /61 exact. This will match any prefix that falls within the /61 range. You also need to delete the export statement under protocols isis, because this will export all routes that match the policy statement to other IS-IS routers, which is not desired for a summary route.

In the context of Ethernet VPN (EVPN) and the behavior described in the exhibit, it's essential to understand the different EVPN route types and their specific functionalities. Here, CE-2 is receiving unicast traffic on both of its multihomed links to PE-2 and PE-3, but broadcast traffic is received only on one of these links.

**Explanation of EVPN Route Types**:

1. **Type 1 (Ethernet Auto-Discovery Routes)**:

- These routes are used for auto-discovery of Ethernet segments and for advertising VLAN membership.

- They do not directly influence the behavior described in the question.

2. **Type 2 (MAC/IP Advertisement Routes)**:

- These routes are used to advertise MAC addresses and IP-to-MAC bindings within the EVPN.

- They handle unicast traffic forwarding and are crucial for populating the MAC address tables on the PE devices.

- While important, they do not explain the selective broadcast behavior.

3. **Type 3 (Inclusive Multicast Ethernet Tag Routes)**:

- These routes are used to build multicast distribution trees for delivering broadcast, unknown unicast, and multicast (BUM) traffic.

- They ensure that BUM traffic is sent only once per Ethernet segment, preventing duplicate frames from being sent to multihomed CEs.

- This aligns with the behavior described where CE-2 receives broadcast traffic on only one link to prevent duplication.

4. **Type 4 (Ethernet Segment Routes)**:

- These routes are used to advertise the presence of an Ethernet segment and are crucial for Designated Forwarder (DF) election processes in multihoming scenarios.

- While relevant to multihoming, they are not directly responsible for the selective broadcast behavior.

**Conclusion**:

The behavior described, where CE-2 receives broadcast traffic on only one of its multihomed links, is controlled by Type 3 routes. These routes are specifically designed to handle inclusive multicast and broadcast traffic efficiently in EVPN environments, ensuring that such traffic is not duplicated across multiple links to the same CE.

**References**:

- Juniper Networks EVPN Documentation: [EVPN Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/evpn-overview.html)

- RFC 7432, BGP MPLS-Based Ethernet VPN: [RFC 7432](https://tools.ietf.org/html/rfc7432) provides detailed descriptions of EVPN route types and their functions.

- Junos OS EVPN Configuration Guide: [Junos OS EVPN Configuration Guide](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/evpn.html)

IS-IS is a link-state routing protocol that uses the Dijkstra algorithm to compute the shortest paths between nodes in a network. The Dijkstra algorithm maintains three data structures: a tree database, a candidate database, and a link-state database (LSDB). The tree database contains the nodes that have been visited and their shortest distances from the source node. The candidate database contains the nodes that have not been visited yet and their tentative distances from the source node. The LSDB contains the topology information of the network, such as the links and their costs.

The Dijkstra algorithm works as follows:

The local router moves its own local tuples into the tree database. A tuple consists of a node ID, a distance, and a parent node ID. The local router’s tuple has a distance of zero and no parent node.

The local router moves its neighbors’ tuples into the candidate database. The neighbors’ tuples have distances equal to the costs of the links to them and parent node IDs equal to the local router’s node ID.

The local router selects the tuple with the lowest distance from the candidate database and moves it to the tree database. This tuple becomes the current node.

The local router updates the distances of the current node’s neighbors in the candidate database by adding the current node’s distance to the link costs. If a shorter distance is found, the parent node ID is also updated.

The algorithm repeats steps 3 and 4 until either the destination node is reached or the candidate database is empty.