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

https://www.juniper.net/documentation/us/en/software/junos/static-routing/topics/ref/statement/qualified-next-hop-edit-routing-options.html

https://www.juniper.net/documentation/us/en/software/junos/static-routing/topics/topic-map/static-route-prefer-qualified-next-hop.html: Qualified next hops allow you to associate one or more properties with a particular next-hop address. You can set an overall preference for a particular static route and then specify a different preference for the qualified next hop. For example, suppose two next-hop addresses (10.10.10.10 and 10.10.10.7) are associated with the static route 192.168.47.5/32. A general preference is assigned to the entire static route, and then a different preference is assigned to only the qualified next-hop address 10.10.10.7. For example:

The qualified-next-hop statement with a static route is used to specify multiple next hops for a static route with different preferences (priorities). This allows for more granular control over the path selection process in the event that the primary next hop becomes unreachable.References:

• Static Routes Overview, Juniper Networks Documentation
• Example: Configuring Qualified Next Hop, Juniper Networks Documentation

The policy statement shown in the exhibit has a term that specifiesload-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.

References:

• Juniper Networks documentation on Load Balancing: Load Balancing Overview

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13684-12.html#anc13

Neighbors Stuck in Exstart/Exchange State The problem occurs most frequently when you attempt to run OSPF between a Cisco router and another vendor router. The problem occurs when the maximum transmission unit (MTU) settings for neighboring router interfaces do not match. If the router with the higher MTU sends a packet larger that the MTU set on the neighboring router, the neighbor router ignores the packet. When this problem occurs, the output of the show ip ospf neighbor command displays output similar to what is shown in this figure.

A mismatched Maximum Transmission Unit (MTU) setting on OSPF interfaces can cause routers to get stuck in the ExStart state. OSPF requires that both sides of a link have the same MTU to form a full adjacency.References:

• OSPF Troubleshooting, Juniper Networks Documentation
• MTU and OSPF, Juniper Networks Documentation

When you want to advertise an interface in OSPF but not form an OSPF adjacency over that interface (for example, towards an ISP), you can configure the interface as passive. This will advertise the network on the interface in OSPF without sending OSPF hello packets or forming OSPF neighbor relationships on that interface.

References

• Juniper Networks Technical Documentation on OSPF
• OSPF Configuration Guide - Juniper Networks

In VRRP (Virtual Router Redundancy Protocol), the router with the highest priority is elected as the master (primary) router. In the exhibit, routers R1 and R4 are both configured with a VRRP priority of 90. Since R2 and R3 have default priorities (which are lower than 90), they will not be elected over R1 or R4. Between R1 and R4, if all else is equal, the router with the numerically higher IP address becomes the master. However, if not enough information is provided to determine which of R1 or R4 has the higher IP address, the answer would be the one explicitly mentioned with the highest priority.

References:

• Juniper Networks documentation on VRRP: VRRP Overview

static route with a next-hop of next-table pointing to the appropriate routing table which contains more accurate information rib-groups to mirror routing information from one route-table to another. However, in many cases, in order to make this work, interface-routes also need to be mirrored. RIB Group policy can be used to constrain the routing information instance-import and instance-export statements configured within the individual routing-instances to leak routes from one table to another. Again, policy can be used here to constrain the routing information. This method is more straightforward than the rib-group method A final approach is to use physical interfaces or logical-tunnels to stitch routing-instances and use a routing protocol or static routes across this connection between the two routing-instances.

To share routes between two routing instances on a Junos device, you can configure an instance import policy in one or both instances to import routes from the other instance. Alternatively, a RIB (Routing Information Base) group can be used to share routes between instances.References:

• Routing Instances Overview, Juniper Networks Documentation
• RIB Groups Configuration Guide, Juniper Networks Documentation

To enable MPLS on a physical interface in Junos, the family mpls statement must be added to the interface configuration. Additionally, the interface itself must be specifiedunder the protocols mpls section of the configuration.References:

• MPLS Configuration Guide, Juniper Networks Documentation
• Configuring MPLS, Juniper Networks Documentation

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.

References:

• Juniper Networks documentation on Segment Routing: Segment Routing Overview
• Juniper Networks technical documentation providing guidance on configuring OSPF with Segment Routing extensions.
• IETF RFC 8665: OSPF Extension for Segment Routing.

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.

References:

• Juniper Networks documentation on OSPF: OSPF Overview

the Database Description (DD) packets serve two main purposes:

1. determinining which router is in charge of the database synchronization

2. tansferring the LSA headers between the two systems

The Database Description (DBD) OSPF packet is used during the adjacency formation process to describe the contents of the topological database between routers. The routers exchange DBD packets to determine the master and slave relationship, which dictates the router in charge of the database synchronization.References:

• OSPF Design Guide, Juniper Networks Documentation
• OSPF Database Description Packets, Juniper Networks Documentation

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.References:

• MPLS Traffic Engineering, Juniper Networks Documentation
• Traffic Engineering and LSP Optimization, Juniper Networks Documentation

In OSPF, a totally stubby area does not permit type 3 summary LSAs (inter-area routes) or type 5 external LSAs (routes from outside the OSPF domain) to be flooded into the area. The area border router (ABR) will only send a default route as a type 3 LSA into the totally stubby area.

References:

• Juniper Networks documentation on OSPF Areas: Understanding OSPF Areas

In the given exhibit, interfacege-0/0/0is configured to accept VLANs 101-120 andge-0/0/1is configured with flexible VLAN tagging, which means it can tag traffic with any VLAN ID specified. However, only VLAN 200 is explicitly mentioned forge-0/0/1.A. Traffic tagged with VLAN 101 will pass throughge-0/0/0and will egress onge-0/0/1with the same VLAN tag, because the VLAN ID is within the allowed range on both interfaces.B. VLAN 100 is not specified in the allowed VLAN range forge-0/0/0(which is 101-120),nor is it specified underge-0/0/1. Therefore, it will be dropped.References:

• Understanding VLAN Tagging, Juniper TechLibrary
• Configuring VLANs for EX Series Switches, Juniper TechLibrary

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.References:

• Understanding BGP Path Selection, Juniper TechLibrary
• BGP Policies and Route Selection, Juniper TechLibrary

https://www.juniper.net/documentation/us/en/software/junos/mpls/topics/topic-map/lsp-routers.html

In an MPLS network, the types of routers include ingress routers (where the MPLS labels are first applied), egress routers (where MPLS labels are removed), and transit routers (which switch MPLS-labeled packets through the MPLS network). Peering routers andaggregation routers are not specific types of MPLS routers; they are general network terms.

References:

• Juniper Networks documentation on MPLS: MPLS Fundamentals

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

Thenext-hop-self-policypolicy is used to alter the next-hop attribute of BGP routes. When you apply it as an export policy to an external BGP (eBGP) group, it changes the next-hop attribute of the routes being advertised to eBGP neighbors so that the next-hop IP address is the IP address of the router itself. This ensures that the eBGP neighbors use the local router as the next hop to reach these routes.

References

• Juniper Networks Technical Documentation on BGP Policies

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.References:

• Filter-Based Forwarding Overview, Juniper Networks Documentation
• Example: Configuring Filter-Based Forwarding, Juniper Networks Documentation

When establishing an EBGP session, it's necessary to specify both the local AS number and the local address that the session will use. The local address is required for establishing the TCP connection for BGP. The local AS must be specified to identify the autonomous system of the router.References:

• Configuring BGP, Juniper TechLibrary
• BGP Peers and BGP Sessions, Juniper TechLibrary

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 notre-advertised to another IBGP peer. This behavior is designed to prevent routing information loops within the same AS.

References:

• Juniper Networks documentation on BGP: BGP Route Propagation and Selection

The AS path is a BGP attribute that lists the autonomous systems (AS) that routing information has passed through to get to a destination. It is used to detect and prevent routing loops by checking if the router's own AS number is in the path.

References:

• Juniper Networks documentation on BGP: BGP Attributes and Policy

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

Theipandgrinterface types are used as endpoints for various tunneling protocols.ipis a generic term that can refer to any IP-based tunnel, whilegrspecifically refers to Generic Routing Encapsulation (GRE) tunnel interfaces in Junos.

References:

• Juniper Networks documentation on Interface Types: Interface Types and Their Default Properties