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Question 161:

Which OSPF feature is used to reduce the amount of routing information advertised between areas?

1. Route summarization
2. Route reflection
3. MAC learning
4. VLAN tagging

Correct Answer: 1

Explanation:

OSPF route summarization reduces the amount of routing information that needs to be advertised between areas by representing multiple more-specific prefixes with a summarized prefix. This is particularly useful in larger OSPF deployments where many networks exist within individual areas. Summarization can reduce routing-table size and limit the propagation of individual topology changes outside the originating area. In Junos, routing policy and OSPF configuration can be used together to control how routes are advertised. Careful planning is required because an overly broad summary can affect reachability. Route summarization is fundamentally different from BGP route reflection, which is designed to improve the scalability of iBGP session relationships.

Question 162:

Which OSPF state indicates that routers have successfully exchanged their link-state databases and formed a full adjacency?

1. Init
2. 2-Way
3. Full
4. Down

Correct Answer: 3

Explanation:

The OSPF Full state indicates that neighboring routers have completed database synchronization and have established a fully formed adjacency. During the OSPF adjacency process, routers progress through several states as they discover each other, exchange database information, and synchronize their link-state databases. Reaching Full indicates that the routers have successfully completed the required synchronization process. On certain network types, not every neighbor necessarily reaches Full with every other router because DR and BDR behavior affects adjacency formation. When troubleshooting OSPF, examining the neighbor state can quickly identify where the adjacency process is stopping.

Question 163:

Which OSPF packet is primarily used to exchange summaries of the link-state database between neighbors?

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

Correct Answer: 2

Explanation:

OSPF Database Description packets are used during adjacency formation to exchange summaries of the link-state database between neighboring routers. These packets contain information describing available link-state advertisements rather than carrying the complete LSAs themselves. After comparing the database summaries, a router can determine which LSAs it needs and request them using Link State Request packets. Hello packets are used for neighbor discovery and maintenance, while Link State Acknowledgment packets confirm receipt of LSAs. Understanding these packet types is useful for troubleshooting OSPF adjacency formation because problems during database exchange can prevent neighbors from reaching the Full state.

Question 164:

Which BGP attribute is commonly used to tag routes so that routing policies can identify them later?

1. Community
2. Next hop
3. MED
4. Router ID

Correct Answer: 1

Explanation:

BGP communities provide a convenient mechanism for tagging routes with values that can later be matched by routing policies. An administrator can apply a community to a group of routes and then use that community as a policy match condition. This allows large numbers of prefixes to be handled consistently without creating individual policy terms for every destination. Communities are commonly used for traffic engineering, route filtering, controlling advertisements, and communicating routing information between different parts of a network. They do not directly identify the physical next hop or router interface. Their primary role is to provide flexible route classification for policy processing.

Question 165:

Which BGP attribute is generally preferred when its value is lower, assuming the routes are otherwise comparable and the attribute is considered?

1. Local preference
2. MED
3. AS path
4. Community

Correct Answer: 2

Explanation:

The Multi-Exit Discriminator, or MED, is generally preferred when its value is lower when comparing otherwise eligible routes from the same neighboring autonomous system. MED can be used to influence which entry point a neighboring AS should prefer when multiple connections exist between the two autonomous systems. Administrators can set MED values through routing policy to influence inbound traffic engineering. MED should not be confused with local preference, where a higher value is preferred within the local autonomous system. Because BGP route selection involves multiple attributes and implementation rules, administrators should consider the complete decision process rather than relying on MED alone.

Question 166:

Which BGP attribute is normally propagated within an autonomous system through iBGP and is used to influence outbound traffic?

1. MED
2. Local preference
3. Router ID
4. Origin

Correct Answer: 2

Explanation:

Local preference is used within an autonomous system to influence which exit point should be selected for outbound traffic. A higher local preference value is normally preferred during BGP path selection. Because local preference is propagated through iBGP, routers within the same autonomous system can use a common policy for choosing preferred external paths. Administrators often configure local preference based on the desired primary and backup connections to external networks. For example, routes learned through a preferred provider can be assigned a higher local preference than routes learned through a backup provider. This provides a predictable method for controlling outbound traffic without modifying every individual router’s configuration.

Question 167:

Which Junos command can be used to examine detailed information about a specific BGP neighbor?

1. show bgp neighbor
2. show ospf database
3. show lldp neighbors
4. show arp

Correct Answer: 1

Explanation:

The show bgp neighbor command provides detailed operational information about BGP neighbor relationships. It can display session information, negotiated capabilities, timers, route statistics, protocol state, and other details useful for troubleshooting. While show bgp summary provides a concise overview of multiple peers, the neighbor command is more useful when an administrator needs to investigate one particular BGP session in depth. For example, it can help identify whether the session reached Established state and provide information about routes exchanged and session parameters. Detailed BGP operational commands are important when diagnosing peer connectivity, policy behavior, or unexpected route exchange.

Question 168:

What is the primary purpose of a BGP import policy?

1. To control routes received from a BGP neighbor
2. To assign power to an IP phone
3. To establish an OSPF adjacency
4. To create a VXLAN tunnel

Correct Answer: 1

Explanation:

A BGP import policy controls how routes received from a BGP neighbor are processed before they are accepted into the local routing system. The policy can match characteristics such as prefixes, communities, AS paths, or other route attributes and then accept, reject, or modify the matching routes. Import policies are important for filtering unwanted routes and implementing routing decisions based on business or technical requirements. For example, an organization may accept only specific prefixes from an external provider. Import policies should be carefully designed because an incorrect filter can prevent legitimate routes from entering the routing table and cause connectivity problems.

Question 169:

What is the primary purpose of a BGP export policy?

1. To control which routes are advertised to a BGP neighbor
2. To synchronize OSPF LSDBs
3. To power Ethernet devices
4. To classify voice packets

Correct Answer: 1

Explanation:

A BGP export policy controls which routes a router advertises to a BGP neighbor. It can match prefixes, communities, route attributes, or other characteristics and then determine whether the routes should be advertised or rejected. Export policies are important for preventing accidental route leaks and ensuring that only authorized or appropriate networks are announced to external peers. For example, an organization may advertise only its own address space to an ISP. Routing policies can also modify attributes before advertisement when required for traffic engineering. Careful export filtering is an important part of maintaining secure and predictable BGP operations.

Question 170:

Which EVPN route type advertises MAC and IP reachability for an endpoint?

1. Route Type 3
2. Route Type 1
3. Route Type 2
4. Route Type 4

Correct Answer: 3

Explanation:

EVPN route type 2 is the MAC/IP Advertisement route and is used to advertise endpoint MAC and IP reachability information. This route type is fundamental to EVPN because it allows participating devices to learn where endpoints are located without relying solely on traditional data-plane flooding. In an EVPN-VXLAN deployment, a VTEP can advertise MAC and IP information through the EVPN control plane, allowing remote VTEPs to build the required forwarding information. Route type 1 is associated with Ethernet Auto-Discovery, route type 3 with Inclusive Multicast Ethernet Tag information, and route type 4 with Ethernet Segment information.

Question 171:

Which EVPN route type is used to advertise Ethernet Segment information for multihoming?

1. Route Type 2
2. Route Type 4
3. Route Type 3
4. Route Type 1

Correct Answer: 2

Explanation:

EVPN route type 4 is the Ethernet Segment route and is used to advertise information about an Ethernet segment participating in an EVPN multihoming environment. This information allows provider edge devices to discover other PE devices connected to the same Ethernet segment. It supports important multihoming functions, including coordination between participating devices and Designated Forwarder election. EVPN multihoming provides redundant connectivity and can improve availability for connected endpoints. Route type 4 should be distinguished from route type 1, which is used for Ethernet Auto-Discovery information, and route type 2, which advertises MAC/IP reachability for endpoints.

Question 172:

In an EVPN-VXLAN architecture, what is the role of the IP underlay network?

1. It provides IP connectivity between VTEPs
2. It stores all endpoint MAC addresses
3. It performs user authentication
4. It replaces the EVPN control plane

Correct Answer: 1

Explanation:

The IP underlay provides the basic Layer 3 connectivity required between VTEPs in an EVPN-VXLAN network. VXLAN encapsulated packets are transported across this routed infrastructure, while the EVPN control plane provides information about virtual networks and endpoint reachability. Keeping the underlay relatively simple and routed allows the overlay to provide flexible Layer 2 and Layer 3 services without requiring the physical network to become one large Layer 2 domain. The underlay does not replace the EVPN control plane because EVPN provides important control-plane information for endpoint and segment reachability. A stable and reachable underlay is therefore fundamental to a reliable VXLAN fabric.

Question 173:

Which protocol is used by VXLAN to transport encapsulated Ethernet frames across an IP network?

1. TCP
2. UDP
3. ICMP
4. ARP

Correct Answer: 2

Explanation:

VXLAN uses UDP as its transport protocol for carrying encapsulated Ethernet frames across an IP network. The original Ethernet frame is encapsulated with VXLAN information and transported inside an IP/UDP packet between VTEPs. UDP provides the transport mechanism while VXLAN supplies the overlay encapsulation and VNI information. This design allows Layer 2 traffic to traverse a Layer 3 IP underlay. Understanding the encapsulation format is useful when troubleshooting VXLAN connectivity because administrators need to verify IP reachability between VTEPs as well as the appropriate VXLAN and EVPN configuration. VXLAN itself does not use TCP as its normal transport protocol.

Question 174:

Which Junos feature can be used to provide Layer 3 connectivity between VLANs?

1. IRB interface
2. LLDP
3. MAC RADIUS
4. PoE

Correct Answer: 1

Explanation:

An Integrated Routing and Bridging, or IRB, interface provides Layer 3 gateway functionality for a VLAN or switching segment. Hosts in different VLANs can use their respective IRB interfaces as default gateways, allowing the device to route traffic between those VLANs. IRB interfaces are commonly used in enterprise switching environments and are also important in EVPN-VXLAN designs where Layer 3 gateway functionality is required for virtual networks. The IRB interface combines bridging and routing functionality within the switching architecture. LLDP provides neighbor discovery, MAC RADIUS provides authentication, and PoE provides electrical power, so none of those technologies perform the Layer 3 gateway function.

Question 175:

Which mechanism helps prevent unauthorized devices from gaining unrestricted access to an enterprise switch port?

1. 802.1X authentication
2. VXLAN encapsulation
3. OSPF SPF
4. BGP MED

Correct Answer: 1

Explanation:

802.1X provides port-based network access control and can prevent an endpoint from receiving normal network access until authentication requirements are satisfied. The switch acts as an authenticator and communicates with an authentication server, commonly using RADIUS. Based on the authentication result, the network can apply appropriate authorization and access policies. This is particularly useful in enterprise environments where administrators need to control access for users and devices connecting to physical switch ports. 802.1X does not encrypt all network traffic by itself and does not perform routing. It is an access-control mechanism that works alongside other security technologies.

Question 176:

Which technology can be used as an alternative authentication method for endpoints that do not support 802.1X?

1. MAC-based authentication
2. OSPFv3
3. EVPN
4. VXLAN

Correct Answer: 1

Explanation:

MAC-based authentication can provide a method of controlling network access for endpoints that cannot participate in 802.1X authentication. Devices such as printers, certain IoT devices, and specialized equipment may not have the necessary supplicant capabilities for 802.1X. In a MAC-based authentication deployment, the access device can use the endpoint’s MAC address as an identity and communicate with a centralized authentication server. The resulting authentication or authorization decision can determine the access policy applied to the endpoint. Although convenient, MAC authentication has security limitations because MAC addresses can potentially be spoofed, so it should be combined with appropriate network-security controls.

Question 177:

Which CoS mechanism determines how much bandwidth a queue can receive relative to other queues?

1. Scheduler
2. LLDP
3. RADIUS
4. Routing policy

Correct Answer: 1

Explanation:

A CoS scheduler controls how traffic queued for transmission receives available interface resources. Scheduling parameters can determine the relative treatment and bandwidth allocation among queues, especially when the interface is congested. Different forwarding classes can be mapped to different queues, and schedulers can then provide differentiated service based on the network’s requirements. For example, delay-sensitive voice traffic may receive more favorable scheduling than ordinary best-effort traffic. Schedulers work alongside classifiers, forwarding classes, policers, shaping, and drop profiles. They do not determine routing paths or authenticate users. Correct scheduler design is important for maintaining predictable application performance during congestion.

Question 178:

What is the primary purpose of a CoS policer?

1. To enforce a configured traffic rate
2. To calculate the OSPF shortest path
3. To discover network neighbors
4. To advertise EVPN routes

Correct Answer: 1

Explanation:

A CoS policer monitors traffic and enforces a configured rate or bandwidth limit. When traffic exceeds the permitted rate, the policer can take a configured action, such as dropping packets or changing their treatment. Policing is commonly used to prevent a particular traffic source or class from consuming more bandwidth than intended. It can be applied as part of an overall quality-of-service design. A policer differs from a scheduler, which determines how queued traffic receives transmission resources, and from a shaper, which generally buffers traffic to smooth its transmission rate. Understanding these distinctions is important when troubleshooting bandwidth-control behavior.

Question 179:

Which Junos command is useful for checking the ARP entries associated with IPv4 neighbors?

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

Correct Answer: 1

Explanation:

The show arp command displays Address Resolution Protocol information maintained by the Junos device for IPv4 neighbors. ARP maps IPv4 addresses to Layer 2 MAC addresses on directly connected networks. This information is important for determining whether the device can resolve a local IPv4 destination to an Ethernet destination address. If an expected ARP entry is missing or incorrect, connectivity problems may occur even when the routing table contains the correct route. Administrators can use ARP information together with interface and routing commands to isolate problems involving local IPv4 reachability. The Ethernet switching table serves a different purpose by displaying learned Layer 2 MAC information.

Question 180:

Which Junos command allows an administrator to compare the candidate configuration with the currently committed configuration?

1. show route
2. show | compare
3. show arp
4. show interfaces terse

Correct Answer: 2

Explanation:

The show | compare command is useful in Junos configuration mode for viewing differences between the current candidate configuration and the active committed configuration. It allows administrators to review pending changes before committing them. This is especially valuable when making multiple configuration modifications because it helps identify unintended changes or missing statements. Reviewing the differences before a commit can reduce configuration mistakes and make troubleshooting easier. After verifying the changes, the administrator can use the appropriate commit command to activate them. Operational commands such as show route or show arp provide network-state information and do not perform candidate-versus-active configuration comparisons.