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

Junos devices learn about MAC addresses by examining the source MAC address of frames received on an interface and then storing these MAC addresses in the MAC address table (also known as the forwarding database) along with the interface on which the traffic was received.References:

• Understanding Learning and Forwarding, Juniper TechLibrary
• MAC Address Table Processing, Juniper TechLibrary

The exhibit shows theshow vrrp summaryoutput from two routers, with both routers listing the state of their VRRP group asmaster. VRRP allows for multiple routers to share a virtual IP address and a virtual MAC address, but usually, only one router is the master at any given time while others are in backup state. However, in some configurations, VRRP can operate in an active/active mode where multiple routers handle traffic simultaneously for load sharing. Since both routers show the state asmasterand there is no evidence of misconfiguration in the virtual IP addresses or priority, it indicates that VRRP is likely functioning in an active/active setup.

References:

• Juniper documentation on VRRP: Junos OS 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

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

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 routershave 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

In OSPF, an Area Border Router (ABR) that connects to a Not-So-Stubby Area (NSSA) will convert the Type 7 LSAs generated by an NSSA Autonomous System Boundary Router (ASBR) into Type 5 LSAs to advertise them into the OSPF backbone area (Area 0). Type 7 LSAs are specific to NSSAs and are used to advertise external routes within the NSSA.

References:

• Juniper Networks documentation on OSPF: OSPF Areas and LSA Types Explained

To configure OSPFv3 (the version of OSPF that supports IPv6), you would use theset protocols ospf3command with the appropriate area and interface. OSPFv3 requires a 32-bit router ID just like OSPFv2, which is typically an IPv4 address. OSPF does not use a 128-bit router ID, so answer D is incorrect.

References:

• Juniper Networks documentation on OSPFv3: OSPFv3 Overview

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

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

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

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

The "ultimate-hop-popping" term refers to the action taken by the penultimate router in an LSP to remove the MPLS label before delivering the packet to the ultimate router,which is not desired here. Configuring the "explicit-null" statement causes the penultimate router to replace the top label with a label that has a value of 0, which instructs the ultimate router to perform a label lookup and preserve the label switching for the entire LSP.

References:

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

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

Referring to the configuration in the exhibit, R1 is set to export the 3rd_Policy to the neighbor at 192.168.1.5. Since 3rd_Policy permits the 10.200.3.0/24 prefix, only that prefix will be advertised to the neighbor.References:

• BGP Policies, Juniper Networks Documentation
• Policy Framework, Juniper Networks Documentation

only 10.200.3.0/24 will be advertised. The neighbor export overrides anything at the group level and protocol level. Policies aren't additive, you can't apply all three at the same time. What if one of them rejected a prefix while the other accepted the same one? You need one to override the other

The exhibit shows the configuration of a virtual switch calledsw-1with two VLANs defined within it:vlan_1with VLAN ID 1 andvlan_2with VLAN ID 2. To add interfacexe-1/0/5to the virtual switch, the interface must be associated with one of these VLANs. Since the interface is already configured withvlan-id 2, it implies that it is intended to be part ofvlan_2within the virtual switchsw-1. Therefore, the correct answer is to add interfacexe-1/0/5to thevlan_2bridge domain under thesw-1routing instance.

References:

• Juniper documentation on virtual switches: Junos OS Routing Instances Overview

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

https://zartmann.dk/sr-intro/

In segment routing, SIDs (Segment Identifiers) are used to identify different types of segments that can be traversed. A node SID represents an instruction to route a packet to a particular node, and an adjacency SID represents an instruction to route a packet over a specific link or adjacency between two nodes.

References

• Juniper Networks Technical Documentation on Segment Routing

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

By default, the router that originally sourced the route into BGP places its peer address into the attribute field. The next-hop value is then typically changed when the route is transmitted across external gGP (EBGP) links. Internal BGP (IBGP) peers do not alter the next-hop value between themselves.

B. By default, the next-hop value is changed when a route is passed from an EBGP peer to another EBGP peer.C. By default, the next-hop value is retained when a route is advertised across IBGP links.References:

• BGP Next Hop Attribute, Juniper TechLibrary
• Understanding BGP Next-Hop Selection, Juniper TechLibrary

When deploying Link Aggregation Groups (LAGs), it is necessary for all ports in the LAG to operate at the same speed to ensure consistent performance and avoid issues with load balancing. Multi-Chassis LAG (MC-LAG) allows for the use of member links that span multiple physical devices, offering redundancy and higher bandwidth by combining the links from two separate devices into a single logical LAG.

References

• Juniper Networks Technical Documentation on Link Aggregation Groups
• Juniper Networks Technical Documentation on MC-LAG

To influence the path taken through an autonomous system, the Multi-Exit Discriminator (MED) attribute can be used. By setting a lower MED on R2 for routes advertised toR1 and R3, it will make the path through R2 to the 203.0.113.0/24 network more preferable.References:

• Understanding BGP Path Selection, Juniper TechLibrary
• BGP Attributes and Path Selection, Juniper TechLibrary

For IS-IS to form adjacencies, the 'family iso' statement must be configured on the interface. This is required because IS-IS operates over the connectionless network service (CLNS) and not over IP. Without the 'family iso' configuration, IS-IS cannot form adjacencies over the interface.

References:

• Juniper Networks documentation on IS-IS: IS-IS User Guide for Routing Devices