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

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

The FE80::/10 prefix is reserved for IPv6 link-local addresses. These addresses are auto-configured on all IPv6-enabled interfaces and can be used for communication within the local link (subnet) only.

References

• Juniper Networks Technical Documentation on IPv6 Addressing

Segment routing labels can be distributed by link-state routing protocols such as IS-IS and OSPF, which have been extended to support segment routing capabilities.References:

• Segment Routing Overview, Juniper Networks Documentation
• Understanding Segment Routing with OSPF, Juniper Networks Documentation
• Understanding Segment Routing with IS-IS, Juniper Networks Documentation

In MPLS (Multiprotocol Label Switching) networks, routers use label switching to forward packets. The first router at the edge of the MPLS network (R1) will perform a lookup in the mpls.0 table to determine the label to attach to the packet as it enters the MPLS network. This label informs the next routers in the MPLS network (like R2) on how to forward the packet. Internal MPLS routers, like R2, also perform lookups in their mpls.0 table to determine how to switch the packet toward its destination (label swapping). The inet.3 table is used for resolving next-hop information for labeled routes, but it's the mpls.0 table that is used for label switching decisions.

References:

• Juniper Networks documentation on MPLS: MPLS Applications User Guide for Routing Devices

Upon a link failure in an RSVP-signaled LSP, the router upstream of the failure (R2) sends a PathTear message upstream to the ingress router (R1), and the router downstream of the failure (R3) sends a ResvTear message downstream to the egress router (R4). These messages signal the failure and initiate tear down of the LSP state in the respective directions.References:

• RSVP-TE Overview, Juniper Networks Documentation
• Understanding RSVP Signal Failures, Juniper Networks Documentation

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

The Segment Routing Global Block (SRGB) defines a range of MPLS labels reserved for segment routing. With an SRGB starting label of 10,000 and an index range of 500, the first usable label is indeed 10,001 because label 10,000 is typically reserved and not usedfor forwarding. The last usable label would be 10,499 because the range includes 500 labels starting from 10,001.

References:

• Juniper Networks documentation on Segment Routing: Segment Routing Overview

The exhibit shows the output of the commandshow spanning-tree bridge, which provides information about the spanning tree status of the switch. From the output, we can see that the switch has a bridge ID different from the root ID, which implies that this switch is not the root bridge. The "Topology change initiator" field shows ge-0/0/14, which indicates that the last topology change occurred on this interface, and this is also the interface used to reach the root bridge.

References:

• Juniper Networks documentation on Spanning Tree Protocol: Understanding Spanning Tree Protocols

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

You can see area 0.0.0.1 set for one interface and area 0.0.0.0 for the other interface. This means the router communicates in the backbone and area 1, thus it is an ABR.

Default hello timer and dead intervals are configured

hello-interval—Specifies the length of time, in seconds, before the routing device sends a hello packet out of an interface. By default, the routing device sends hello packets every 10 seconds. The range is from 1 through 255 seconds.

dead-interval—Specifies the length of time, in seconds, that the routing device waits before declaring that a neighboring routing device is unavailable. This is an interval during which the routing device receives no hello packets from the neighbor. By default, the routing device waits 40 seconds (four times the hello interval). The range is 1 through 65,535 seconds.

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/configuring-ospf-timers.html#:~:text=The%20hello%20interval%20and%20the,devices%20on%20a%20shared%20network .

C. The R2 device is shown as having interfaces in two different OSPF areas (Area 0 and another area not specified), which makes it an Area Border Router (ABR).D. The OSPF hello and dead intervals are set to their default values of 10 and 40 seconds, respectively.References:

• Understanding OSPF Areas and ABRs, Juniper TechLibrary
• OSPF Configuration Guide, Juniper TechLibrary

The exhibit shows that the BGP session state is "Active," which generally indicates that the router is trying to establish a BGP session but has not received a response. One common cause for this issue is that there is no route to the BGP neighbor's address. Since the routers are using internal BGP (iBGP) and they are in the same AS, the AS number does not need to be unique, and anext-hop selfpolicy is not strictly required for iBGP. Therouter-idis usually automatically determined and does not need to be explicitly set.

References:

• Juniper Networks documentation on BGP: Troubleshooting BGP

In BGP (Border Gateway Protocol), the Update message is used to advertise new routes to a peer or to withdraw previously advertised routes. If there's a change in the routing information or if a new route needs to be advertised, BGP uses an Update message. This message is crucial for maintaining the most current and accurate routing information among BGP peers.

The other message types serve different purposes:

Keepalive: This message type is used to maintain the connection between BGP peers and ensure that the link is still active. Keepalive messages are periodically sent between peers when there is no other BGP activity to maintain the session.

Notification: This message is used to indicate errors or other significant events to a BGP peer. If a BGP error condition is detected, a Notification message is sent and the BGP session is typically closed.

Refresh: This is not a standard BGP message type. However, in the context of BGP, Route Refresh is a capability (not a message type) that allows a BGP router to request a full or partial re-advertisement of routes from a peer. This helps in re-synchronizing routing tables without tearing down the BGP session.

The BGP Update message is used to advertise routable destinations and includes route advertisements, route withdrawals, and path attribute modifications. Update messages are used to re-advertise routes that have already been acknowledged.References:

• BGP Operations and Message Types Overview, Juniper Networks Documentation
• BGP Update Message, Juniper Networks Documentation

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

In Junos OS, traffic engineering extensions for OSPF, which are required for an LSP to use the OSPF link state database for path computations, are not enabled by default. They must be explicitly enabled in the OSPF configuration. Therefore, answer C is correct. Answer B is incorrect and contradicts C. The 'no-cspf' command would disable CSPF (Constrained Shortest Path First), which is used for path computations in MPLS traffic engineering, so it should not be used if you want the LSP to utilize OSPF's link state database for path computations. Therefore, answer A is incorrect. The 'policing' parameter is not relevant to enabling traffic engineering extensions in OSPF, so answer D is incorrect.

References:

• Juniper Networks documentation on OSPF and Traffic Engineering: Configuring OSPF Traffic Engineering

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/configuring-ospf-support-for-traffic-engineering.html

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.

References:

• Juniper Networks documentation on BGP communities: BGP Communities Overview

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.References:

• MPLS Fundamentals, Juniper Networks Documentation
• RSVP-TE Signaling, Juniper Networks Documentation

To test connectivity to a server from within a specific routing instance, you use thepingcommand along with therouting-instanceoption to specify the routing instance from which you are pinging. This is necessary because the routing table associated withvr3is separate from the main routing table, and you must explicitly tell the device to use thevr3routing table to reach the server.

References:

• Juniper Networks documentation on Routing Instances: Routing Instances Overview

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

https://www.networkfuntimes.com/junos-aggregate-routes-vs-generate-routes-how-to-summarise-on-juniper-routers/

Generated routes are a type of route that can be created to summarize and generate more specific routes within the routing table. Unlike aggregate routes, which summarize existing routes and inherit a next-hop, generated routes do not necessarily have to match an existing route and will have a next-hop of reject by default unless specified otherwise.

References

• Juniper Networks Technical Documentation on Routing Policies and Route Generation

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

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

An Integrated Routing and Bridging (IRB) interface is used to provide Layer 3 routing services to hosts within a bridge domain. The IRB acts as a default gateway for hosts in that domain, enabling communication with other networks.

References

• Juniper Networks Technical Documentation on IRB Interfaces