View Full Juniper JN0-637 Exam Dumps and Practice Test Dumps

 

Question 281. Which BGP feature allows a router to install multiple equal-cost BGP paths for the same destination?

1. Route reflection
2. BGP synchronization
3. BGP multipath
4. AS path prepending

Correct Answer: 3. BGP multipath

Explanation:
BGP multipath allows Junos devices to install multiple eligible BGP routes to the same destination when the paths satisfy the configured multipath requirements. Instead of selecting only one best path, the routing system can use multiple paths for forwarding, which can provide load sharing and improved utilization of available links. The paths generally need compatible attributes and must meet the platform’s BGP multipath criteria. This feature is particularly useful in networks with redundant upstream connections or multiple equal-cost paths between autonomous systems. BGP multipath is different from route reflection, which primarily reduces the iBGP full-mesh requirement.

Question 282. What is the primary purpose of the BGP next-hop self configuration?

1. To make the local router the BGP next hop for advertised routes
2. To disable BGP route advertisements
3. To increase the MED value automatically
4. To convert eBGP sessions into iBGP sessions

Correct Answer: 1. To make the local router the BGP next hop for advertised routes

Explanation:
The next-hop self configuration causes a BGP router to advertise itself as the next hop when sending routes to a BGP neighbor. This is especially useful in iBGP designs where the original next-hop address learned from an external peer may not be reachable by internal routers. By setting itself as the next hop, the router ensures that downstream routers can resolve the forwarding path through it. This configuration is commonly used on route-reflector clients or internal routers that advertise externally learned routes into the rest of an autonomous system. It does not disable advertisements or change an eBGP session into an iBGP session.

Question 283. Which BGP community is intended to prevent a route from being advertised outside the local autonomous system?

1. NO_EXPORT
2. NO_ADVERTISE
3. INTERNET
4. NOPEER

Correct Answer: 4. NO_ADVERTISE

Explanation:
The well-known BGP NO_ADVERTISE community instructs a receiving BGP speaker not to advertise the route to any other BGP peers. This provides a mechanism for controlling the propagation of a particular route. NO_EXPORT has a different scope: it prevents a route from being advertised outside a confederation or autonomous system, depending on the routing context. The INTERNET community indicates that the route can be advertised normally, while NOPEER is used to restrict advertisement to peer relationships. Correctly applying BGP communities allows operators to implement granular routing policies without changing the underlying network topology.

Question 284. In a BGP route-reflector design, what is the main purpose of route reflection?

1. To replace IP routing with MPLS forwarding
2. To eliminate the requirement for a full iBGP mesh
3. To automatically encrypt BGP sessions
4. To increase the AS path length of reflected routes

Correct Answer: 2. To eliminate the requirement for a full iBGP mesh

Explanation:
BGP route reflection reduces the need for every iBGP router in an autonomous system to maintain a direct session with every other iBGP router. A route reflector receives routes from its clients and reflects eligible routes to other clients and non-client peers according to BGP rules. This significantly simplifies large-scale iBGP deployments and reduces the number of required sessions. Route reflection does not provide encryption, replace IP routing with MPLS, or intentionally increase the AS path length. Route reflectors use attributes such as the cluster ID and originator ID to help prevent routing loops within the route-reflector architecture.

Question 285. Which IS-IS packet type is used to establish and maintain neighbor adjacencies?

1. CSNP
2. LSP
3. PSNP
4. IIH

Correct Answer: 4. IIH

Explanation:
IS-IS uses Intermediate System-to-Intermediate System Hello, or IIH, packets to establish and maintain neighbor relationships. These packets allow IS-IS routers to discover one another and exchange information needed to form adjacencies. Once adjacencies are established, routers exchange Link State PDUs and use sequence-number mechanisms to maintain a synchronized link-state database. CSNPs summarize the link-state database, while PSNPs request or acknowledge specific link-state information. LSPs carry the actual link-state information. Therefore, IIH is the packet type directly associated with neighbor discovery and adjacency maintenance in IS-IS.

Question 286. What is the primary role of a Designated Intermediate System (DIS) in an IS-IS broadcast network?

1. To perform IP address assignment
2. To act as the only default gateway
3. To represent the LAN in the link-state database
4. To replace all Level 2 routers

Correct Answer: 3. To represent the LAN in the link-state database

Explanation:
On an IS-IS broadcast network such as an Ethernet LAN, the Designated Intermediate System (DIS) represents the LAN as a pseudonode in the link-state database. The DIS creates and maintains a pseudonode LSP that represents the connectivity between the participating routers on that LAN. This approach reduces the number of individual point-to-point relationships that would otherwise need to be represented in the topology database. The DIS is not a default gateway, does not assign IP addresses, and does not replace Level 2 routers. Its role is specifically related to efficient link-state representation on multiaccess networks.

Question 287. What information is primarily carried in an IS-IS Link State PDU (LSP)?

1. Link-state and reachability information
2. Only Ethernet MAC addresses
3. Only BGP community values
4. DHCP lease information

Correct Answer: 1. Link-state and reachability information

Explanation:
IS-IS Link State PDUs contain the link-state information that routers use to build and maintain the IS-IS link-state database. This information can include router connectivity, reachability prefixes, metrics, and other topology-related information carried through IS-IS TLVs. Each router uses the collected information to calculate paths through the network. LSPs are not limited to Ethernet MAC addresses and do not carry DHCP lease information. BGP communities are attributes associated with BGP routes rather than the primary content of IS-IS LSPs. Accurate LSP flooding is essential for maintaining a consistent topology view among participating IS-IS routers.

Question 288. What is the primary purpose of an IS-IS Complete Sequence Number PDU (CSNP)?

1. To establish the first TCP session with a neighbor
2. To advertise BGP routes
3. To summarize the contents of the link-state database
4. To assign MPLS labels

Correct Answer: 3. To summarize the contents of the link-state database

Explanation:
A Complete Sequence Number PDU, or CSNP, provides a summary of the link-state information known by an IS-IS router. On broadcast networks, the DIS periodically sends CSNP information so other routers can compare their databases with the information represented in the CSNP. If a router identifies missing or outdated LSP information, appropriate requests or updates can be exchanged. CSNPs therefore contribute to database synchronization and consistency. They are not used to establish TCP sessions, advertise BGP routes, or assign MPLS labels. PSNPs serve a different purpose by requesting or acknowledging specific LSP information.

Question 289. What is the purpose of a Partial Sequence Number PDU (PSNP) in IS-IS?

1. To request or acknowledge specific LSP information
2. To create an MPLS forwarding label
3. To establish an OSPF adjacency
4. To assign a DIS priority

Correct Answer: 1. To request or acknowledge specific LSP information

Explanation:
Partial Sequence Number PDUs, or PSNPs, are used by IS-IS routers to request missing or outdated LSP information and to acknowledge receipt of specific LSPs. This allows routers to maintain synchronization of their link-state databases without having to exchange the entire database every time a discrepancy is detected. CSNPs provide a broader summary of database contents, while PSNPs focus on specific LSPs. PSNPs are part of IS-IS database synchronization and do not create MPLS labels, establish OSPF adjacencies, or assign DIS priority. Their use helps ensure that the participating routers maintain consistent topology information.

Question 290. Which MPLS label operation is normally performed when a transit router forwards a labeled packet through an MPLS LSP?

1. Push
2. Pop
3. Encrypt
4. Swap

Correct Answer: 4. Swap

Explanation:
A transit MPLS router commonly performs a label swap operation. It examines the incoming label, uses its forwarding information to determine the appropriate outgoing interface and label, removes the incoming top label, and replaces it with the outgoing label. This allows the packet to continue along the established label-switched path. A push operation adds a label, while a pop operation removes a label. Encryption is not an MPLS label operation. Label swapping is one of the fundamental operations performed by Label Switching Routers in the MPLS core and enables efficient forwarding based on labels rather than repeated IP route lookups.

Question 291. What is the purpose of Penultimate Hop Popping (PHP) in an MPLS network?

1. To add a second label at the egress
2. To remove the outer MPLS label before the egress router
3. To increase the BGP local preference
4. To establish an IS-IS adjacency

Correct Answer: 2. To remove the outer MPLS label before the egress router

Explanation:
Penultimate Hop Popping, or PHP, allows the router immediately before the MPLS egress router to remove the outer MPLS label. The egress router can then process the packet without having to perform the final label-pop operation itself. This can reduce processing requirements at the egress and is commonly used in MPLS forwarding architectures. PHP concerns MPLS label handling and does not modify BGP local preference or establish IS-IS adjacencies. The exact label behavior depends on the label-switched path and the label distribution mechanism being used, but the key concept is removal of the outer label at the penultimate hop.

Question 292. In an MPLS Layer 3 VPN, what is the main purpose of a Route Distinguisher (RD)?

1. To make otherwise overlapping VPN prefixes unique
2. To determine the MPLS outgoing interface
3. To select the BGP MED value
4. To identify the physical router chassis

Correct Answer: 3. To make otherwise overlapping VPN prefixes unique

Explanation:
A Route Distinguisher, or RD, is used in MPLS Layer 3 VPNs to make otherwise identical customer prefixes unique within the VPNv4 or VPNv6 address space. For example, two different customers can both use the same private prefix, while different RDs distinguish those routes in the provider’s multiprotocol BGP control plane. The RD itself does not determine the physical outgoing interface, select the BGP MED value, or identify a router chassis. Route Targets serve a different role by controlling which VPN routes are imported into or exported from VRFs.

Question 293. What is the primary purpose of a BGP Route Target in an MPLS Layer 3 VPN?

1. To identify the physical PE interface
2. To control VPN route import and export
3. To replace the Route Distinguisher
4. To calculate the IGP shortest path

Correct Answer: 4. To control VPN route import and export

Explanation:
Route Targets are extended BGP communities used to control the import and export of VPN routes between provider-edge devices and VRFs. An export Route Target can be attached to routes leaving a VRF, while import policies determine which routes are accepted into a VRF based on matching Route Targets. This allows VPN connectivity to be controlled according to the desired customer topology. Route Targets are different from Route Distinguishers: RDs provide uniqueness for overlapping prefixes, whereas RTs influence VPN route membership and distribution. They do not calculate IGP shortest paths or identify physical interfaces.

Question 294. Which Junos command displays the configured routing policy statements under the policy-options hierarchy?

1. show interfaces terse
2. show route forwarding-table
3. show configuration policy-options
4. show chassis hardware

Correct Answer: 1. show configuration policy-options

Explanation:
The show configuration policy-options command displays the configuration beneath the Junos policy-options hierarchy. This area commonly contains routing policy statements, prefix lists, communities, AS path definitions, and related policy objects. Reviewing this configuration is useful when troubleshooting route import, export, filtering, or attribute manipulation. show interfaces terse provides a concise interface status view, show route forwarding-table displays forwarding information, and show chassis hardware displays hardware inventory. Using the correct operational command helps engineers distinguish between the configured policy and the operational routing state.

Question 295. What is the primary function of a Junos routing policy then statement?

1. To define the conditions that must match
2. To specify the actions taken when a route matches
3. To create a physical interface
4. To establish an OSPF adjacency

Correct Answer: 2. To specify the actions taken when a route matches

Explanation:
In Junos routing policies, the from section defines match conditions, while the then section defines the action taken when those conditions are satisfied. Actions can include accepting or rejecting a route, modifying attributes, adding communities, changing local preference, setting MED, or performing other policy operations. Separating match conditions from actions makes routing policies structured and flexible. The then statement does not create interfaces or establish routing protocol adjacencies. Understanding this distinction is essential when troubleshooting why a route is being accepted, rejected, or modified during import or export processing.

Question 296. Which Junos high-availability feature allows the control plane to continue operating during a Routing Engine switchover?

1. GRES
2. LACP
3. RSTP
4. LLDP

Correct Answer: 3. RSTP

Explanation:
RSTP is a Layer 2 spanning-tree protocol and is not the Junos high-availability feature responsible for maintaining control-plane state during a Routing Engine switchover. GRES, or Graceful Routing Engine Switchover, is designed to allow forwarding to continue while the routing control function transitions between Routing Engines. Related high-availability mechanisms such as NSR can preserve protocol state across a switchover. LACP provides link aggregation, while LLDP provides neighbor discovery. Therefore, for control-plane continuity during an RE switchover, GRES and related HA mechanisms are the relevant concepts.

Question 297. Which technology allows Junos devices to collect and stream operational telemetry data to an external collector?

1. SNMP polling only
2. Static routing
3. NETCONF configuration
4. Streaming telemetry

Correct Answer: 2. Static routing

Explanation:
Static routing does not provide telemetry collection or streaming capabilities. Streaming telemetry is specifically designed to continuously send operational data from a network device to an external collector. Depending on the Junos platform and configured telemetry framework, data can include interface statistics, routing information, system health metrics, and other operational values. NETCONF is primarily a protocol used for structured configuration and management, although it can be part of broader automation workflows. SNMP can also provide monitoring data, but traditional SNMP commonly relies on polling. Streaming telemetry is designed for more continuous, efficient data delivery.

Question 298. Which Junos mechanism can be used to automatically revert a configuration change if it is not confirmed within the specified interval?

1. commit confirmed
2. show | compare
3. rollback 0
4. load override

Correct Answer: 4. load override

Explanation:
load override does not provide automatic rollback after an unconfirmed commit. In Junos, commit confirmed is the mechanism that temporarily commits a configuration while requiring confirmation within a specified period. If the administrator does not issue a normal commit before the timer expires, Junos automatically rolls back to the previous committed configuration. This feature is particularly useful when making remote configuration changes because it reduces the risk of permanently losing management access. show | compare compares configuration states, while rollback commands manipulate stored configurations but do not provide the same timed confirmation mechanism.

Question 299. Which Junos CoS component determines the forwarding class or loss priority based on packet characteristics?

1. Scheduler
2. Rewrite rule
3. Classifier
4. Policer

Correct Answer: 3. Classifier

Explanation:
A CoS classifier examines packet characteristics and maps traffic into forwarding classes and, where applicable, loss-priority values. Classification can be based on information such as DSCP, IEEE 802.1p markings, or other packet fields depending on the configured classifier. Once traffic is classified, other CoS components determine how it is queued, scheduled, and potentially remarked. A scheduler controls transmission resources, while a rewrite rule changes packet markings before transmission. A policer controls traffic according to configured rate parameters. Therefore, the classifier is the component responsible for assigning traffic to the appropriate forwarding treatment.

Question 300. What is the purpose of a CoS rewrite rule on a Junos device?

1. To establish BGP peering
2. To change packet classification markings before transmission
3. To calculate an OSPF shortest path
4. To create an IS-IS LSP

Correct Answer: 1. To establish BGP peering

Explanation:
A CoS rewrite rule does not establish BGP peering. Its purpose is to modify or rewrite packet CoS markings before packets leave an interface. For example, a device can rewrite DSCP or 802.1p values to reflect the desired forwarding treatment in a downstream network. Classification determines how traffic is internally categorized, while rewriting can change the markings carried in the transmitted packet. BGP peering is a routing control-plane function, and OSPF and IS-IS perform link-state routing functions. CoS rewrite rules therefore belong to the traffic-classification and forwarding-treatment portion of the network configuration.