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Question 121:

Which OSPF packet type is used to discover and maintain neighbor relationships?

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

Correct Answer: 3

Explanation:

OSPF uses Hello packets to discover neighboring routers and maintain neighbor relationships. Routers periodically send Hello packets through OSPF-enabled interfaces, allowing other routers on the same network segment to learn about their presence and verify that the adjacency parameters match. Hello packets contain information such as the router ID, area, hello interval, dead interval, and other configuration details. If the required parameters are incompatible, an adjacency may fail to form. The Hello protocol is therefore fundamental to OSPF neighbor discovery and maintenance. Other OSPF packet types perform database synchronization, flooding, and acknowledgment functions after neighbor relationships are established.

Question 122:

Which OSPF component contains the link-state information used by the SPF algorithm?

1. ARP table
2. LSDB
3. MAC address table
4. Forwarding class

Correct Answer: 2

Explanation:

The Link-State Database, or LSDB, contains the link-state information that OSPF routers use to build their view of the network topology. Each OSPF router maintains an LSDB for each relevant area and uses the information contained in it to calculate shortest paths using the SPF algorithm. OSPF routers exchange link-state advertisements to synchronize their databases. If the LSDB is incomplete or inconsistent, routing calculations may produce incorrect or missing routes. The LSDB should not be confused with the routing table, which contains selected routes, or the forwarding table, which is used to forward packets. Understanding the relationship between LSDB, SPF, and routing tables is important for troubleshooting OSPF.

Question 123:

What is the primary purpose of an OSPF area?

1. To divide the OSPF topology into logical regions
2. To replace the IP routing table
3. To identify a BGP peer
4. To provide Ethernet encryption

Correct Answer: 1

Explanation:

OSPF areas divide an OSPF autonomous system into logical regions. This hierarchical structure helps reduce the amount of link-state information that needs to be maintained and processed by routers. Routers within an area maintain detailed topology information for that area, while summarized information can be exchanged between areas through area border routers. Area 0, known as the backbone area, plays a central role in inter-area OSPF communication. Proper area design can improve scalability and reduce unnecessary SPF calculations. When troubleshooting OSPF, administrators should verify that interfaces and routers are assigned to the intended areas and that the required area relationships are correctly established.

Question 124:

Which OSPF router role connects one OSPF area to another area?

1. Internal router
2. Designated router
3. Area Border Router
4. Backup designated router

Correct Answer: 3

Explanation:

An Area Border Router, or ABR, has interfaces participating in more than one OSPF area and provides connectivity between those areas. ABRs maintain separate link-state information for their connected areas and can advertise inter-area routing information. They are especially important in hierarchical OSPF designs where multiple non-backbone areas connect through the OSPF backbone. An internal router belongs entirely to one area, while a designated router and backup designated router are roles associated with certain multi-access network segments. Understanding ABR behavior is important when troubleshooting inter-area routes because incorrect area configuration or backbone connectivity can prevent expected routes from being advertised.

Question 125:

Which OSPF network type commonly uses a DR and BDR election on a broadcast multi-access network?

1. Broadcast
2. Point-to-point
3. Loopback
4. Passive

Correct Answer: 1

Explanation:

OSPF uses a Designated Router and Backup Designated Router on broadcast multi-access networks to reduce the number of full adjacency relationships required between routers. Ethernet networks are a common example of a broadcast multi-access environment. Instead of every router forming a full adjacency with every other router, routers establish the appropriate relationships with the DR and BDR, which helps reduce OSPF control-plane overhead. The BDR provides redundancy if the DR becomes unavailable. Point-to-point networks generally do not require DR or BDR elections because only two OSPF neighbors are expected on the link. Correctly identifying the network type is useful when troubleshooting unexpected OSPF adjacency behavior.

Question 126:

Which BGP attribute represents the sequence of autonomous systems through which a route has passed?

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

Correct Answer: 3

Explanation:

The AS path attribute records the sequence of autonomous systems associated with a BGP route advertisement. It provides important information for BGP path selection and also helps prevent routing loops. When an external BGP route is advertised from one autonomous system to another, the originating AS information is added to the AS path. A router can detect its own autonomous system number in the path and reject the route, helping prevent the route from being accepted back into the same AS. The AS path can also influence route selection, with shorter paths generally being preferred when comparing otherwise eligible routes. Routing policies can additionally manipulate or evaluate this attribute.

Question 127:

What is the main purpose of a BGP community attribute?

1. To identify physical interfaces
2. To group routes for policy processing
3. To calculate OSPF SPF
4. To assign Ethernet MAC addresses

Correct Answer: 2

Explanation:

BGP communities provide a method for grouping routes so that routing policies can act on them efficiently. Instead of writing separate policies for every individual prefix, an administrator can attach a community value to related routes and then match that community in routing policy. Communities are commonly used for traffic engineering, route tagging, controlling route advertisements, and communicating routing intentions between BGP peers. A route can carry one or multiple community values. Communities themselves do not determine the physical interface or MAC address of a packet. Their primary value is in providing flexible policy classification and control within BGP environments.

Question 128:

Which BGP session type is established between routers belonging to different autonomous systems?

1. iBGP
2. eBGP
3. OSPF
4. EVPN

Correct Answer: 2

Explanation:

External BGP, or eBGP, is used to exchange routing information between routers belonging to different autonomous systems. It is commonly used between an enterprise and an ISP or between different organizations that exchange routing information. Internal BGP, or iBGP, is used between BGP speakers within the same autonomous system. The distinction is important because eBGP and iBGP have different operational characteristics and are often used for different design purposes. For example, an enterprise may use eBGP to connect to an upstream provider while using iBGP internally to distribute external routing information among its own routers.

Question 129:

Which routing protocol is commonly used as the underlay protocol in a VXLAN EVPN fabric?

1. BGP
2. FTP
3. RADIUS
4. LLDP

Correct Answer: 1

Explanation:

BGP is commonly used as the control-plane protocol for EVPN and can be used to distribute EVPN reachability information across a VXLAN fabric. In a typical architecture, the IP underlay provides basic IP connectivity between VTEPs, while BGP EVPN provides the overlay control plane. The separation between underlay and overlay allows the network to use a scalable routed infrastructure while providing Layer 2 and Layer 3 virtual network services over it. EVPN routes communicate endpoint and segmentation information, while VXLAN provides the encapsulation mechanism for carrying tenant traffic across the IP network.

Question 130:

What is the primary benefit of VXLAN compared with traditional VLAN-only segmentation in large data-center networks?

1. It provides greater logical segmentation scalability
2. It eliminates the need for IP routing
3. It replaces Ethernet switching
4. It disables multicast traffic

Correct Answer: 1

Explanation:

VXLAN provides a scalable mechanism for creating logical Layer 2 segments across a Layer 3 IP infrastructure. Traditional VLAN identifiers have a limited numerical space, while VXLAN uses a much larger VNI space, making it suitable for large-scale data-center environments. VXLAN also allows Layer 2 connectivity to be extended across routed underlay networks without requiring the entire physical infrastructure to operate as one large Layer 2 domain. EVPN is commonly paired with VXLAN to provide a control plane for endpoint reachability and other information. VXLAN does not eliminate IP routing; instead, it uses the IP underlay to transport encapsulated overlay traffic.

Question 131:

Which EVPN route type is associated with Ethernet Auto-Discovery information?

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

Correct Answer: 3

Explanation:

EVPN route type 1 is the Ethernet Auto-Discovery route. It is used in EVPN environments to advertise information associated with Ethernet segments and is particularly important for multihoming scenarios. Ethernet Auto-Discovery information helps EVPN devices understand the presence and reachability of Ethernet segments connected through provider edge devices. Other EVPN route types have different purposes. Route type 2 advertises MAC and IP reachability information, while route type 3 provides Inclusive Multicast Ethernet Tag information. Route type 4 is associated with Ethernet Segment information used for multihoming operations. Understanding these route types helps administrators interpret EVPN control-plane tables during troubleshooting.

Question 132:

Which EVPN route type is specifically associated with Ethernet Segment discovery?

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

Correct Answer: 1

Explanation:

EVPN route type 4 is the Ethernet Segment route. It is used to advertise Ethernet Segment information among participating EVPN devices and plays an important role in EVPN multihoming. Through this control-plane information, devices can discover other provider edge routers participating in the same Ethernet segment. This information supports functions such as multihoming coordination and Designated Forwarder election. Route type 4 should be distinguished from route type 1, which provides Ethernet Auto-Discovery information, and route type 2, which advertises MAC/IP reachability. Understanding the purpose of each EVPN route type is essential when analyzing BGP EVPN advertisements and troubleshooting multihomed network designs.

Question 133:

Which component provides the Layer 3 routing functionality associated with an EVPN-VXLAN virtual network?

1. VTEP
2. IRB interface
3. LLDP neighbor
4. RADIUS server

Correct Answer: 2

Explanation:

An Integrated Routing and Bridging, or IRB, interface can provide Layer 3 gateway functionality for a virtual network in an EVPN-VXLAN architecture. Hosts within a VLAN or VXLAN segment can use the IRB interface as their default gateway, allowing traffic to be routed between different virtual networks or toward external destinations. The VTEP handles VXLAN encapsulation and decapsulation, while the IRB interface provides the Layer 3 gateway function. This separation allows EVPN-VXLAN fabrics to support both Layer 2 bridging and Layer 3 routing services. Proper IRB configuration is therefore important when implementing inter-VLAN or inter-VNI communication.

Question 134:

Which Junos feature allows an administrator to control route import and export behavior based on defined conditions?

1. Routing policy
2. LLDP
3. PoE
4. STP

Correct Answer: 1

Explanation:

Junos routing policies provide flexible control over how routes are accepted, modified, rejected, or advertised. Policies can match characteristics such as prefixes, protocol, route attributes, communities, or other routing information and then perform actions such as accepting or rejecting routes or modifying attributes. Routing policies are widely used with protocols such as BGP and OSPF to implement specific routing requirements. For example, a policy can restrict which prefixes are advertised to an external BGP peer or modify local preference for selected routes. Proper policy design is essential because an incorrectly configured policy can unintentionally suppress routes or advertise prefixes that should remain internal.

Question 135:

Which BGP policy action would prevent a matched route from being accepted?

1. Accept
2. Reject
3. Next-hop self
4. Metric increase

Correct Answer: 2

Explanation:

A reject action prevents a matched route from being accepted by the policy. Junos routing policies commonly use match conditions followed by actions that determine how the route should be handled. If a route matches a term containing a reject action, that route is denied according to the policy processing rules. Rejecting routes can be useful for filtering unwanted prefixes, preventing unauthorized advertisements, or implementing routing security requirements. Administrators should carefully test policies before applying them because an overly broad rejection condition can remove valid routes from consideration. Understanding the difference between accepting, rejecting, and modifying routes is fundamental to effective Junos routing policy configuration.

Question 136:

Which authentication method commonly uses a centralized server to verify network-user credentials?

1. RADIUS
2. VXLAN
3. OSPF
4. EVPN

Correct Answer: 1

Explanation:

RADIUS is a centralized authentication, authorization, and accounting protocol commonly used to control network access. A network device can forward authentication information to a RADIUS server, which verifies the credentials and can return authorization information. Centralized authentication simplifies account management because administrators can maintain authentication information on dedicated servers rather than creating independent credentials on every network device. RADIUS is widely used in enterprise environments for network access control and can work with technologies such as 802.1X and MAC-based authentication. It is not a routing or tunneling protocol, so it does not exchange OSPF, BGP, or EVPN routes.

Question 137:

What is the main purpose of 802.1X in an enterprise access network?

1. Port-based network access authentication
2. VXLAN packet encapsulation
3. BGP route selection
4. OSPF database synchronization

Correct Answer: 1

Explanation:

IEEE 802.1X provides port-based network access control by requiring an endpoint to authenticate before receiving normal network access. In a typical deployment, the endpoint acts as the supplicant, the switch acts as the authenticator, and a RADIUS server performs authentication. This architecture allows organizations to control which devices and users can access protected network resources. Depending on the configuration, successful authentication can result in assignment of specific access policies, VLANs, or other authorization attributes. 802.1X is therefore an important enterprise security mechanism. It does not perform routing, VXLAN encapsulation, or OSPF database synchronization.

Question 138:

Which CoS component determines the treatment applied to packets based on characteristics such as DSCP or 802.1p markings?

1. Classifier
2. Scheduler
3. Policer
4. Shaper

Correct Answer: 1

Explanation:

A CoS classifier examines characteristics of incoming packets and assigns them to appropriate traffic categories. Depending on the configured classifier, packet markings such as DSCP or 802.1p can be used to determine the forwarding class and packet loss priority. This classification becomes the basis for subsequent CoS processing, including queue selection and scheduling. A scheduler controls how queues receive transmission resources, while a policer enforces traffic-rate limits. A shaper smooths traffic transmission according to a configured rate. Understanding these functions helps administrators troubleshoot why a packet is receiving a particular queue, priority, or bandwidth treatment.

Question 139:

What is the primary purpose of traffic shaping in a CoS implementation?

1. To smooth traffic by controlling the transmission rate
2. To establish BGP sessions
3. To discover LLDP neighbors
4. To create OSPF areas

Correct Answer: 1

Explanation:

Traffic shaping controls the rate at which traffic is transmitted, helping smooth bursts and manage how traffic is released onto an interface. Unlike a mechanism that simply discards traffic exceeding a rate, shaping generally buffers traffic so that it can be transmitted according to the configured rate when resources become available. This can help reduce congestion and make traffic behavior more predictable. Shaping is often used as part of a broader CoS design involving forwarding classes, queues, schedulers, and drop profiles. Correct configuration is important because an overly restrictive shaping rate can introduce unnecessary delay or reduce the throughput available to applications.

Question 140:

Which command is most useful for checking whether an interface is operational and viewing its basic link state in Junos?

1. show route
2. show interfaces terse
3. show bgp summary
4. show ospf database

Correct Answer: 2

Explanation:

The show interfaces terse command provides a concise overview of interfaces and their operational and administrative states. It is one of the most useful initial commands when troubleshooting interface connectivity because it quickly shows whether an interface is up or down and provides basic information about logical units. If an expected interface is not operational, the administrator can then use more detailed commands such as show interfaces extensive to investigate physical errors, statistics, or configuration details. The other commands focus on routing or protocol information rather than basic interface status. Checking interface state is often an essential first step before troubleshooting higher-level network protocols.