JN0-363 Sample Questions Answers

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

On a Junos device, trunk ports are configured to receive and transmit tagged traffic only, while access ports are configured to receive and transmit untagged traffic.References:

• Understanding Access and Trunk Interfaces, Juniper Networks Documentation
• VLANs and Trunking, Juniper Networks Documentation

https://www.catchpoint.com/bgp-monitoring/bgp-attributes

BGP Attribute Categories

There are four categories of BGP attributes:

Well-known mandatory:Recognized by all BGP peers, passed to all peers, and present in all Update messages. Well-known mandatory attributes include:- Next-hop- Origin- AS PATH

Well-known discretionary:Recognized by all routers, passed to all peers, and optionally included in the Update message. Well-known discretionary attributes include:- Local Preference- Atomic Aggregate

Optional transitive:Possibly recognized by BGP routers and passed to BGP peers. Optional transitive attributes are marked as partial when not recognized. Optional transitive attributes include:- Aggregator- Community

Optional non-transitive:Possibly recognized by BGP routers but not passed to peers. Optional non-transitive attributes include:- Multi-exit discriminator (MED)- Originator ID- Cluster-ID

The three well-known mandatory BGP attributes that must be present in every BGP update message are:

• Next Hop: Indicates the next hop IP address to reach the advertising BGP peer.
• Origin: Indicates how the route was originated, whether it was via IGP, EGP, or incomplete.
• AS Path: Lists the autonomous systems that the update has traversed.

References

• Juniper Networks Technical Documentation on BGP Attributes

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 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

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

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

metric—Metric value. Range: 1 through 63, or 1 through 16,777,215 (if you have configured wide metrics) Default: 10 (for all interfaces except lo0), 0 (for the lo0 interface)

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.

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 Ethernet switching, learning and aging are two fundamental concepts for maintaining a dynamic Ethernet switching table (also known as a MAC address table). Learning is the process by which switches listen for frames and learn the MAC addresses by associating them with the incoming port. Aging is the mechanism that ensures the switch updates its table by removing MAC addresses that have not been seen for a certain amount of time (aging time).

References:

• Juniper documentation on Ethernet switching: Understanding Ethernet Switching on Junos OS Devices

In the OSPF routing table output, prefixes are marked with different route types. An external prefix injected into OSPF is marked as 'Ext' (External) followed by a number that indicates whether it's an E1 or E2 route. The prefix 172.18.1.0/24 is marked as Ext2, which indicates that it is an external route that has been redistributed into OSPF from another routing protocol or static configuration.

References

• Juniper Networks Technical Documentation on OSPF

The IPv6 header includes a new field that is not found in the IPv4 header, called the flow label. The flow label in IPv6 is used to identify packets that require special handling by routers for quality of service (QoS) or other reasons, allowing these packets to be handled efficiently as they move through the network.

References

• Juniper Networks Technical Documentation on IPv6
• IPv6 Header Fields - Juniper Networks

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

With Label Distribution Protocol (LDP), a full mesh of label-switched paths (LSPs) is automatically created between all LDP-enabled routers, and these paths are reflected in the inet.3 table. LDP LSPs are set up when LDP is enabled on interfaces connecting routers in an MPLS network.

References:

• Juniper Networks documentation on LDP: Understanding LDP

BGP selects the active route based on an ordered list of attributes. The correct order is:

• Weight (Cisco proprietary, not listed in the options)
• Local Preference
• Network (route) originated from the BGP router itself
• Shortest AS Path
• Lowest Origin Type
• Lowest MED
• eBGP over iBGP paths
• Closest IGP Neighbor
• Lowest Router ID

The next hop is checked for reachability but is not part of the BGP decision process for selecting the best path.

References

• Juniper Networks Technical Documentation on BGP

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

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

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

Theno-readvertisepolicy statement is used to prevent a static route from being redistributed into a dynamic routing protocol. This setting ensures that routes that are configured statically are not advertised out via dynamic routing protocols such as OSPF or BGP.

References

• Juniper Networks Technical Documentation on Routing Policy

To prevent a router from participating in the OSPF designated router (DR) and backup designated router (BDR) election process, you set the OSPF priority to 0 on the interfaces of that router. This tells OSPF that the router on those interfaces is not to be considered for election as either DR or BDR, effectively making them DRother routers. The exhibit indicates that this is the desired configuration, and therefore the correct command to issue on the Juniper device would be to set the priority to 0 on the relevant interfaces.