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Question 221:

Which OSPF packet is used to request specific LSAs from a neighboring router when the local router is missing information from its LSDB?

1. Database Description
2. Link State Request
3. Link State Update
4. Link State Acknowledgment

Correct Answer: 2

Explanation:

The OSPF Link State Request (LSR) packet is used when a router needs specific link-state information from a neighboring router. During database synchronization, routers compare their LSDB information using Database Description packets. If a router discovers that it is missing a particular LSA or has an outdated version, it sends an LSR requesting that specific LSA. The neighboring router responds with a Link State Update containing the requested information. This process helps routers maintain consistent link-state databases within an OSPF area. Link State Acknowledgment packets are then used to acknowledge received LSAs.

Question 222:

In Junos OS, which BGP attribute is normally used to influence outbound path selection from an autonomous system by preferring one exit point over another?

1. MED
2. Origin
3. Local Preference
4. AS Path

Correct Answer: 3

Explanation:

Local Preference is a BGP attribute commonly used within an autonomous system to influence which exit path is preferred for outbound traffic. A higher local-preference value is preferred over a lower value when comparing otherwise eligible BGP routes. Because the attribute is carried within the AS, it allows multiple routers to consistently prefer the same external exit point. Network administrators can modify local preference through routing policy. MED is generally used to provide neighboring autonomous systems with a suggestion about preferred entry points, while AS path length and origin are other BGP path-selection attributes.

Question 223:

Which Junos operational command is most useful for verifying the BGP routes learned from a specific BGP neighbor?

1. show route receive-protocol bgp <neighbor>
2. show interfaces terse
3. show ospf database
4. show ethernet-switching table

Correct Answer: 1

Explanation:

The show route receive-protocol bgp <neighbor> command is useful for examining routes received from a particular BGP neighbor. It allows an administrator to verify which routes the neighbor is advertising and can help troubleshoot import policies, route advertisements, and unexpected routing information. This is different from show route, which displays routes installed in the routing table, and show bgp summary, which provides session-level information. When troubleshooting BGP, checking both received routes and installed routes can help determine whether a route was received successfully but later rejected by policy or another routing decision.

Question 224:

What is the primary purpose of a BGP export policy in Junos OS?

1. To determine which routes are accepted from a BGP neighbor
2. To establish the BGP TCP session
3. To determine which routes are advertised to a BGP neighbor
4. To calculate OSPF SPF paths

Correct Answer: 3

Explanation:

A BGP export policy controls which routes a Junos router advertises to a BGP neighbor. The policy can match routes based on prefixes, communities, protocol, route attributes, or other criteria and can then accept, reject, or modify routes before advertisement. This makes export policies an important tool for controlling routing information between autonomous systems or between different parts of a network. An import policy, in contrast, controls routes received from a neighbor. BGP session establishment is handled through the BGP protocol and configuration, while OSPF SPF calculations are unrelated to BGP export policy.

Question 225:

Which EVPN route type advertises MAC and optional IP address information associated with a specific Ethernet segment or MAC-VRF?

1. Ethernet Auto-Discovery
2. Inclusive Multicast Ethernet Tag
3. Ethernet Segment
4. MAC/IP Advertisement

Correct Answer: 4

Explanation:

EVPN Route Type 2 is known as the MAC/IP Advertisement route. It advertises MAC addresses and can also include associated IP address information. This route type is fundamental to EVPN because remote PE or VTEP devices can learn MAC reachability through the EVPN control plane rather than relying entirely on data-plane flooding. Route Type 1 is Ethernet Auto-Discovery, Route Type 3 is Inclusive Multicast Ethernet Tag, and Route Type 4 is Ethernet Segment. In VXLAN EVPN deployments, Type 2 routes are particularly important for distributing endpoint reachability information between VTEPs.

Question 226:

What is the main function of an EVPN Ethernet Segment Identifier (ESI)?

1. To uniquely identify a multihomed Ethernet segment
2. To identify a VXLAN VNI
3. To define an OSPF area
4. To identify a BGP autonomous system

Correct Answer: 1

Explanation:

An Ethernet Segment Identifier, or ESI, identifies an Ethernet segment that can be connected to multiple EVPN PE devices. It is particularly important in EVPN multihoming because several PE devices may provide connectivity to the same customer or downstream Ethernet segment. The ESI allows EVPN devices to recognize that the interfaces belong to the same multihomed segment and supports mechanisms such as designated-forwarder election and split-horizon behavior. An ESI is not the same as a VXLAN VNI, OSPF area identifier, or BGP autonomous-system number. These identifiers serve different purposes within the network architecture.

Question 227:

In a VXLAN EVPN network, which device performs VXLAN encapsulation for traffic entering the VXLAN overlay?

1. Route reflector
2. VTEP
3. RADIUS server
4. OSPF ABR

Correct Answer: 2

Explanation:

A VXLAN Tunnel Endpoint (VTEP) performs VXLAN encapsulation and decapsulation. When a local Ethernet frame needs to reach an endpoint located behind a remote VTEP, the local VTEP encapsulates the original frame inside a VXLAN/UDP/IP packet and sends it across the IP underlay. The remote VTEP removes the VXLAN encapsulation and forwards the original Ethernet frame toward the destination. VTEPs therefore provide the boundary between the traditional Ethernet network and the VXLAN overlay. BGP EVPN can provide the control-plane information that helps VTEPs determine where remote MAC addresses and other endpoint information are located.

Question 228:

Which field identifies the logical VXLAN segment to which an encapsulated Ethernet frame belongs?

1. ESI
2. VNI
3. AS number
4. OSPF Router ID

Correct Answer: 2

Explanation:

The VXLAN Network Identifier (VNI) identifies the VXLAN segment associated with an encapsulated Ethernet frame. A VNI is 24 bits in length and provides a much larger namespace than traditional VLAN identifiers. During VXLAN encapsulation, the VNI is carried in the VXLAN header so the receiving VTEP knows which logical overlay segment the frame belongs to. The ESI has a different role and is associated with EVPN Ethernet segments and multihoming. BGP autonomous-system numbers identify BGP domains, while an OSPF Router ID identifies an OSPF router. These values should not be confused with the VXLAN VNI.

Question 229:

What is the primary purpose of a CoS classifier on a Junos device?

1. To assign traffic to forwarding classes based on packet markings or characteristics
2. To create BGP sessions
3. To perform VXLAN encapsulation
4. To elect an EVPN designated forwarder

Correct Answer: 1

Explanation:

A Class of Service classifier determines how incoming traffic should be categorized for QoS processing. Depending on the configured classification method, the classifier can examine packet markings such as DSCP or 802.1p and map traffic into forwarding classes and packet-loss-priority values. These classifications are then used by downstream CoS components such as schedulers, policers, and drop profiles. Classification is therefore an important first step in providing differentiated treatment to different traffic types. For example, voice traffic can be classified into a forwarding class that receives preferential treatment compared with less-sensitive traffic.

Question 230:

Which CoS mechanism controls how packets are serviced from an output queue?

1. Rewrite rule
2. Scheduler
3. Classifier
4. Routing policy

Correct Answer: 2

Explanation:

A CoS scheduler controls how traffic in output queues is serviced. It can determine factors such as transmission rates, scheduling behavior, and relative treatment of different forwarding classes. This allows a network administrator to provide differentiated bandwidth and priority to applications with different requirements. A classifier determines the forwarding class assigned to traffic, while a rewrite rule changes packet markings as traffic leaves the device. Routing policy is used to control route acceptance, rejection, or modification and is unrelated to queue servicing. Schedulers therefore play a central role in determining how queued traffic receives interface transmission resources.

Question 231:

Which CoS mechanism is designed primarily to smooth traffic by controlling the rate at which packets leave a queue?

1. Shaper
2. MAC authentication
3. OSPF database
4. BGP community

Correct Answer: 1

Explanation:

A traffic shaper regulates the transmission rate of traffic, generally by buffering packets and releasing them according to a configured rate. Shaping can smooth bursts and help prevent traffic from exceeding a desired output rate. Unlike a simple policer, which can discard or otherwise treat packets that exceed configured thresholds, shaping typically works by delaying packets when sufficient bandwidth is temporarily unavailable. This makes shaping useful for managing interface or queue behavior and controlling bandwidth utilization. In a Junos CoS design, shaping can be combined with classifiers, forwarding classes, schedulers, and drop profiles to provide predictable treatment of different traffic types.

Question 232:

What is the main purpose of a CoS rewrite rule?

1. To change outgoing packet classification markings
2. To establish an OSPF adjacency
3. To calculate the BGP best path
4. To assign an IP address to an IRB interface

Correct Answer: 1

Explanation:

A CoS rewrite rule modifies packet markings as traffic leaves a device. For example, a router may internally classify traffic into forwarding classes and then rewrite DSCP or 802.1p values so that downstream devices can recognize the desired service level. This allows QoS information to be preserved or changed as traffic moves between network segments. Classification and rewriting are related but occur at different points in the forwarding process. A classifier determines how traffic should be treated locally, while a rewrite rule changes the markings carried by outgoing packets. Routing protocols and IRB addressing are separate functions.

Question 233:

In Junos CoS, what does Packet Loss Priority (PLP) indicate?

1. The preferred BGP route
2. The relative likelihood that traffic may be dropped during congestion
3. The VXLAN VNI
4. The OSPF neighbor state

Correct Answer: 2

Explanation:

Packet Loss Priority, or PLP, indicates the relative priority of a packet when congestion causes packet loss to become necessary. Traffic marked with a higher loss priority is generally considered a better candidate for dropping than traffic marked with a lower loss priority. PLP can be assigned through classification and can also be influenced by CoS configuration and policies. Drop profiles and queue behavior can then use this information when congestion occurs. PLP does not determine BGP path selection, identify VXLAN segments, or represent an OSPF neighbor state. It is specifically part of Junos Class of Service traffic treatment.

Question 234:

Which access-control method commonly authenticates a device based on its MAC address when 802.1X supplicant authentication is not available?

1. OSPF authentication
2. MAC-based authentication
3. BGP authentication
4. EVPN multihoming

Correct Answer: 2

Explanation:

MAC-based authentication can provide network access control for devices that cannot perform traditional 802.1X supplicant authentication. The switch can use the device’s MAC address as an identity and communicate with an authentication server, commonly through RADIUS, to determine whether access should be permitted. This approach can be useful for devices such as printers, phones, or other equipment that may not support a full 802.1X client. It is different from OSPF or BGP authentication, which protects routing-protocol communication. EVPN multihoming is a Layer 2/overlay networking capability and does not perform endpoint authentication.

Question 235:

What is the purpose of a guest VLAN in an access-control environment?

1. To provide limited network access to unauthenticated or noncompliant devices
2. To replace the OSPF backbone
3. To identify a VXLAN tunnel endpoint
4. To select the BGP best path

Correct Answer: 1

Explanation:

A guest VLAN can provide controlled network access to devices that have not successfully completed the expected authentication process. Instead of granting normal production access, the device may be placed into a restricted VLAN where it can receive limited services, such as access to onboarding or remediation resources. Guest VLAN behavior depends on the configured access-control and authentication design. It is not a replacement for an OSPF backbone and does not participate in BGP path selection. In enterprise networks, guest or fallback access mechanisms can help balance usability with security by preventing unknown endpoints from receiving unrestricted access to production resources.

Question 236:

Which technology is commonly used by an Ethernet switch to provide power to compatible IP phones and other powered devices over the Ethernet cable?

1. LLDP only
2. PoE
3. OSPF
4. BGP

Correct Answer: 2

Explanation:

Power over Ethernet (PoE) allows compatible network devices such as IP phones, wireless access points, and certain cameras to receive electrical power through Ethernet cabling. This can simplify deployment because a separate electrical connection may not be required at every endpoint location. Junos switching platforms that support PoE can provide power according to the device’s capabilities and configured policies. LLDP and LLDP-MED can provide device and network-policy information, but they are not themselves the technology that delivers electrical power. OSPF and BGP are routing protocols and have no role in supplying power to Ethernet endpoints.

Question 237:

Which protocol extension is particularly useful for exchanging information between network switches and IP phones, including voice-related network policies?

1. LLDP-MED
2. BGP
3. OSPFv3
4. LACP

Correct Answer: 1

Explanation:

LLDP-MED extends the capabilities of the Link Layer Discovery Protocol for devices such as IP phones and network infrastructure. It can provide information useful for voice deployments, including network policy details such as the VLAN and QoS treatment intended for voice traffic. This allows compatible endpoints to learn important network configuration information automatically. LLDP-MED is especially useful in enterprise IP telephony environments where voice devices need consistent connectivity and QoS treatment. BGP and OSPFv3 are routing protocols, while LACP is used to negotiate and maintain link aggregation. None of those protocols provide the same endpoint-oriented discovery and voice-policy capabilities as LLDP-MED.

Question 238:

Which OSPF neighbor state indicates that two routers have successfully synchronized their link-state databases and have a fully established adjacency?

1. Init
2. Exchange
3. Full
4. Loading

Correct Answer: 3

Explanation:

The OSPF Full state indicates that neighboring routers have completed database synchronization and have matching relevant link-state information. In this state, the adjacency is considered fully established. Earlier states include Init, where a router has detected a Hello from a neighbor, and Exchange, where Database Description packets are exchanged. During Loading, routers request and receive additional LSAs needed to complete synchronization. Reaching Full is therefore an important indicator when troubleshooting OSPF adjacencies. On certain network types, not every neighboring router necessarily forms a Full adjacency with every other router because OSPF uses designated-router mechanisms to optimize adjacency formation.

Question 239:

Which OSPF command is most appropriate for examining the contents of the link-state database?

1. show bgp summary
2. show ospf database
3. show arp
4. show ethernet-switching table

Correct Answer: 2

Explanation:

The show ospf database command displays information from the OSPF link-state database. This is particularly useful when troubleshooting OSPF because it allows an administrator to examine LSAs and verify whether expected topology information is present. If a route is missing, examining the LSDB can help determine whether the problem originates with LSA generation, flooding, or later route calculation. show bgp summary is used for BGP session information, show arp displays IPv4 address-to-MAC mappings, and show ethernet-switching table displays Layer 2 forwarding information. Therefore, show ospf database is the appropriate command for investigating OSPF LSDB contents.

Question 240:

What is the primary function of an OSPF Area Border Router (ABR)?

1. To connect OSPF areas and exchange routing information between them
2. To provide PoE power to IP phones
3. To assign VXLAN VNIs
4. To authenticate users through RADIUS

Correct Answer: 1

Explanation:

An OSPF Area Border Router, or ABR, connects one OSPF area to another, typically including the backbone Area 0. An ABR maintains link-state information for the areas to which it is connected and can advertise appropriate inter-area routing information between them. This area-based design helps OSPF scale by limiting the amount of topology information that must be maintained throughout the entire routing domain. ABRs can also participate in route summarization between areas when properly configured. PoE, VXLAN VNI assignment, and RADIUS authentication are unrelated functions and are handled by different network technologies.