JN0-363 Service Provider Routing and Switching, Specialist (JNCIS-SP) Questions and Answers

The community attribute in BGP is an optional transitive attribute. It is not mandatory for BGP operations, but when it is present, it should be passed unchanged to other BGP peers unless explicitly modified by a routing policy. The community attribute is used to group destinations in a certain way, often to apply routing policies to those destinations collectively.

By default, BGP will propagate routes learned from EBGP peers to other IBGP peers. However, due to the BGP split-horizon rule, routes learned from one IBGP peer are not re-advertised to another IBGP peer. This behavior is designed to prevent routing information loops within the same AS.

The exhibit shows the configuration of a virtual switch called sw-1 with two VLANs defined within it: vlan_1 with VLAN ID 1 and vlan_2 with VLAN ID 2. To add interface xe-1/0/5 to the virtual switch, the interface must be associated with one of these VLANs. Since the interface is already configured with vlan-id 2 , it implies that it is intended to be part of vlan_2 within the virtual switch sw-1 . Therefore, the correct answer is to add interface xe-1/0/5 to the vlan_2 bridge domain under the sw-1 routing instance.

In IS-IS, Level 1 routes are usually contained within the same area and Level 2 routes are used to interconnect different areas. By default, routes from Level 1 are redistributed into Level 2, and vice versa, to ensure reachability between areas.

References

Juniper Networks Technical Documentation on IS-IS

By default, IS-IS protocol leaks routing information from a Level 1 area to a Level 2 area. However, to leak routing information from a Level 2 area to a Level 1 area, an export policy must be explicitly configured.

The router identifier is used by BGP and OSPF to identify the routing device from which a packet originated. The router identifier usually is the IP address of the local routing device. If you do not configure a router identifier, the IP address of the first interface to come online is used. This is usually the loopback interface. Otherwise, the first hardware interface with an IP address is used

In OSPF, if a router ID is not manually configured, Junos OS will automatically select the router ID based on the highest IP address of any of the router’s loopback interfaces. If no loopback interface exists, the highest IP address of any active interface will be used. Therefore, answer C is correct.

To test connectivity to a server from within a specific routing instance, you use the ping command along with the routing-instance option to specify the routing instance from which you are pinging. This is necessary because the routing table associated with vr3 is separate from the main routing table, and you must explicitly tell the device to use the vr3 routing table to reach the server.

Given the RSVP Signaled Service Provider MPLS Core network shown in the exhibit, only a single Label Switched Path (LSP) is required to support all four networks because MPLS can use label stacking to multiplex multiple LSPs over a single physical path. Therefore, one LSP can be established through the MPLS core, and all networks can use this LSP with different label stacks.

Segment routing is a source routing paradigm that allows a source router to define the path that a packet will take through the network by assigning an ordered list of segments—identifiers that specify a forwarding path for the packet through the network. Segment Routing can be implemented over an MPLS architecture or with IPv6 (SRv6).

A. Segment routing does not require a full mesh of adjacencies or state per transit path in the network, which is often the case with conventional MPLS signaling protocols like RSVP-TE. It leverages the existing IGP topology for forwarding without the need to maintain a state for each LSP (Label Switched Path), hence requiring very little resources to maintain.

B. In segment routing, labels (or segments) are distributed via IGP routing protocols like OSPF or IS-IS with extensions to carry segment routing information. These protocols are enhanced with Segment Routing extensions to distribute labels. For example, OSPFv2 is extended with Segment Routing extensions defined in RFC 8665.

C. This statement is not entirely correct. While it is true that segment routing does not require the maintenance of a state for each path (LSP), the concept of " segment routing adjacencies " is a mischaracterization. Segment routing leverages the existing adjacencies formed by the underlying IGP.

D. Label assignments in segment routing are not advertised through LDP (Label Distribution Protocol) updates. Segment routing does away with LDP and instead uses IGP extensions to distribute labels.

Considering the bandwidth reservations shown, the only path from R4 to R6 that has sufficient available bandwidth for a new LSP with 400 Mbps reservation is via R1, R2, and R5. This is because the R4-R5 direct link and the R4-R1-R2-R3-R6 path do not have enough unreserved bandwidth to accommodate an additional 400 Mbps LSP.

tunnel-end-point name {

ipv4 {

source-address 10.255.1.1;

destination-address 10.255.2.0/25;

}

gre {

key 9;

}

}

https://www.juniper.net/documentation/us/en/software/junos/routing-policy/topics/ref/statement/tunnel-end-point-edit-firewall.html

The ip and gr interface types are used as endpoints for various tunneling protocols. ip is a generic term that can refer to any IP-based tunnel, while gr specifically refers to Generic Routing Encapsulation (GRE) tunnel interfaces in Junos.

The policy statement shown in the exhibit has a term that specifies load-balance per-packet , which indicates that per-packet load balancing is being used. This means that the routing device will distribute packets out multiple paths on a per-packet basis, rather than on a per-flow (per-destination or per-source-destination pair) basis.

Filter-based forwarding in Junos requires the creation of a routing policy to specify the match conditions and actions and the application of a match filter to classify traffic to use the policy.

https://www.juniper.net/documentation/us/en/software/junos/high-availability/topics/task/nsr-configuring.html

Nonstop routing (NSR) requires both Graceful Routing Engine Switchover (GRES) and commit synchronization to be configured to maintain routing protocol and forwarding state during a Routing Engine switchover. NSR allows the secondary Routing Engine to take over the control plane without the protocols needing to restart, and GRES ensures that the forwarding plane continues operating with the current forwarding table. Commit synchronization ensures that configuration changes are synchronized between the primary and backup Routing Engines.

To ensure that MPLS traffic-engineered routes are used without affecting IGP routes in the route tables, the mpls-forwarding traffic engineering setting should be used. This setting allows MPLS to influence forwarding without changing the IGP route selection.

A Level 1 router can become adjacent with the Level 1 and Level 1-2 (L1/L2) router. A Level 2 router can become adjacent with Level 2 or Level 1-2 (L1/L2) router. There is no adjacency between L1 only and L2 only router. HOWEVER: If two routers are in different areas, they can only form a Level 2 adjacency. As such, two routers in different areas can NOT form a Level 1 adjacency. If you want two routers to form a Level 1 adjacency, they have to be in the same area.

IS-IS (Intermediate System to Intermediate System) operates at two levels: Level 1 and Level 2. Level 1 routers are only aware of their own area ' s topology, while Level 2 routers have knowledge of the topology across areas. A Level 1 router cannot form an adjacency with a Level 2 router unless the Level 2 router is also operating as a Level 1 router (Level 1-2 router). Level 2 routers can form adjacencies regardless of their area IDs because Level 2 operates at the domain level and is used to interconnect different IS-IS areas.

References

Juniper Networks Technical Documentation on IS-IS

IS-IS Levels and Areas Explanation - Juniper Networks

The exhibit shows that the Label Switched Path (LSP) is down. One common reason for this could be that the IGP is not providing traffic engineering information to the MPLS process. Since the exhibit shows the OSPF configuration, enabling traffic engineering extensions for OSPF would allow OSPF to distribute the labels and traffic engineering information necessary for LSP establishment.

References

Juniper Networks Technical Documentation on MPLS and OSPF

The show system switchover command is used to display the status of the Graceful Routing Engine Switchover (GRES) feature. This command is available when nonstop routing (NSR) is enabled, which works in conjunction with GRES to maintain uninterrupted routing in case of a Routing Engine switchover.

A route being hidden in BGP usually indicates a configuration that prevents it from being used, such as a next-hop that is not reachable.

B. Configuring a routing policy on R1 that sets the next-hop to the address used for IBGP peering ensures reachability of the next-hop within the local AS.

D. Applying the correct routing policy as an export policy to the IBGP group on R1 will share the route with the IBGP peers, in this case, R2 and R3.

In a service provider MPLS network, P routers are interior routers that are used to transit MPLS-labeled packets between edge routers but do not attach or remove MPLS labels themselves. These routers are also referred to as transit routers. They are neither ingress nor egress routers (which are typically labeled as PE routers).

In MPLS, multiple paths can be merged if they share the same egress router. In the given scenario, traffic from Network 1 to Network 3 and Network 4 can be engineered to follow the same label-switched path (LSP) within the MPLS network until they reach the last common point before diverging to their respective destinations.

As for R3 performing label operations, in a typical MPLS network, intermediate routers (like R3) perform label swapping. They replace the incoming label with a new label before forwarding the packet along the LSP. A label pop operation is typically performed by the egress router in the case of an ultimate hop pop (UHP), where it removes the MPLS label before delivering the packet to the final destination outside the MPLS domain.

References

Juniper Networks Technical Documentation on MPLS

Understanding MPLS Label Operations (Swap, Push, and Pop) - Juniper Networks

IS-IS is a link-state routing protocol that uses a Shortest Path First (SPF) algorithm to create a topology map of the network. It floods link-state advertisements (LSAs) to all nodes within the network area to ensure each node has a consistent view of the network topology.

References

Juniper Networks Technical Documentation on IS-IS

Understanding IS-IS - Juniper Networks