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Question 141:

Which OSPF feature allows a router to advertise a summarized set of routes between areas?

1. Route reflection
2. Area summarization
3. MAC learning
4. VLAN translation

Correct Answer: 2

Explanation:

OSPF area summarization allows routing information to be represented as a summarized prefix rather than advertising every individual subnet separately between areas. This can reduce the amount of routing information exchanged and can make an OSPF network more scalable. Summarization is generally performed at an Area Border Router because an ABR connects multiple OSPF areas. Proper summarization can also help reduce the impact of topology changes because changes to individual routes within a summarized range may not need to be propagated outside the area. However, the summary must be designed carefully so that valid destinations are not unintentionally hidden.

Question 142:

Which OSPF parameter determines how long a router waits before declaring a neighbor unavailable when Hello packets are no longer received?

1. Router ID
2. Dead interval
3. Cost
4. Area ID

Correct Answer: 2

Explanation:

The OSPF dead interval determines how long a router waits without receiving expected Hello packets before declaring its neighbor down. OSPF routers exchange Hello packets periodically to maintain their neighbor relationships. If the configured dead interval expires without receiving an appropriate Hello packet, the neighbor relationship is removed and OSPF recalculates the affected routes. For an adjacency to form correctly, relevant OSPF timer settings must be compatible between neighbors. During troubleshooting, administrators should verify both the Hello interval and dead interval when an expected OSPF adjacency remains down or repeatedly resets.

Question 143:

Which BGP attribute is normally preferred when comparing two otherwise valid routes if one route has a higher local preference?

1. Local preference
2. MED
3. Origin
4. AS path length

Correct Answer: 1

Explanation:

BGP local preference is an important attribute used to influence the preferred exit path from an autonomous system. When comparing otherwise eligible routes, a higher local preference is preferred. This makes local preference particularly useful for controlling outbound traffic within an organization that has multiple external connections. Administrators can apply routing policies to assign different local preference values to routes learned from different providers or peers. Because local preference is propagated through iBGP, routers within the same autonomous system can make consistent path-selection decisions. It is therefore commonly used for internal traffic engineering rather than directly controlling how a neighboring AS sends traffic toward the network.

Question 144:

What is one major advantage of using a BGP route reflector in a large iBGP network?

1. It removes the need for an IP address
2. It reduces the requirement for a full-mesh of iBGP sessions
3. It replaces all external BGP sessions
4. It eliminates routing policies

Correct Answer: 2

Explanation:

A BGP route reflector reduces the need for every iBGP router to establish a direct session with every other iBGP router. In a traditional iBGP design, full-mesh connectivity can become difficult to maintain as the number of routers increases. A route reflector provides a central point through which selected routes can be reflected to other iBGP clients. This improves scalability and simplifies the BGP topology. Route reflectors do not eliminate routing policies or external BGP sessions, and they do not replace the underlying IP connectivity required by BGP. Proper route-reflector design is important to avoid unexpected routing behavior and maintain predictable path selection.

Question 145:

Which BGP attribute is commonly used to prevent routing loops between autonomous systems?

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

Correct Answer: 3

Explanation:

The AS path attribute plays an important role in preventing BGP routing loops. When a route is advertised between autonomous systems, the autonomous system information is added to the AS path. If a BGP router receives a route containing its own autonomous system number in the path, it can recognize that accepting the route would create a loop and reject it. The AS path also provides information about the sequence of autonomous systems a route has traversed and can influence route selection. Although other BGP attributes control traffic engineering and policy decisions, AS path loop detection is one of its fundamental functions.

Question 146:

Which Junos command can be used to display the routes installed in the routing table along with their protocol information?

1. show route
2. show chassis hardware
3. show lldp neighbors
4. show ethernet-switching interfaces

Correct Answer: 1

Explanation:

The show route command displays routing information contained in the Junos routing table. It can provide details such as destination prefixes, next hops, protocol sources, preferences, and other route attributes. Administrators frequently use this command when troubleshooting connectivity because it helps determine whether the router has a route toward a particular destination. Additional command options can narrow the output by protocol, prefix, or other criteria. If a route is missing, the administrator can then investigate the relevant routing protocol, policy, or interface. Understanding the routing table is essential because it represents the routes selected for use by the routing system.

Question 147:

What is the purpose of an OSPF router ID?

1. To uniquely identify an OSPF router within the OSPF domain
2. To assign a VLAN to an interface
3. To identify a RADIUS server
4. To define a BGP community

Correct Answer: 1

Explanation:

The OSPF router ID uniquely identifies an OSPF router within the OSPF routing domain. It is represented as a 32-bit value written in IPv4 address notation, although it does not necessarily represent a reachable interface address. The router ID is used in OSPF control-plane operations, including neighbor relationships and the identification of link-state information. Selecting a stable router ID is important because changes can cause OSPF relationships to reset or require protocol reinitialization. Administrators should therefore ensure that router IDs are unique and predictable across the OSPF topology. A consistent loopback-based design is commonly used to provide stable identification.

Question 148:

Which OSPF mechanism is responsible for calculating the shortest path through the topology?

1. BGP route reflector
2. SPF algorithm
3. RADIUS authentication
4. VXLAN encapsulation

Correct Answer: 2

Explanation:

OSPF uses the Shortest Path First algorithm, commonly called SPF or the Dijkstra algorithm, to calculate the best paths through the link-state topology. The calculation uses information contained in the OSPF Link-State Database. Each router builds a topology representation and calculates shortest paths from itself to reachable destinations. The resulting paths are then considered for installation in the routing table. Changes to the topology can cause SPF calculations to run again so that routing information remains accurate. Efficient OSPF design can help limit unnecessary calculations and improve scalability, especially in networks containing many routers and frequently changing links.

Question 149:

Which Junos command is useful for checking the current BGP peer sessions and their states?

1. show ospf neighbor
2. show interfaces terse
3. show bgp summary
4. show arp

Correct Answer: 3

Explanation:

The show bgp summary command provides a concise overview of BGP sessions configured on a Junos router. It can display information such as peer addresses, autonomous system information, session state, and the number of routes exchanged. This makes it an important first troubleshooting command when a BGP session is not established or when route exchange appears abnormal. If a peer is not in an established state, administrators can investigate issues such as reachability, authentication, AS configuration, routing policies, or transport connectivity. More detailed BGP commands can then be used to examine individual peers and routes after the summary identifies the affected session.

Question 150:

Which protocol is commonly used by Junos devices to discover directly connected neighboring network devices at Layer 2?

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

Correct Answer: 1

Explanation:

The Link Layer Discovery Protocol, or LLDP, allows compatible network devices to exchange information about themselves with directly connected neighbors. This information can include the device identity, interface details, system capabilities, and other management information. LLDP is particularly useful in enterprise environments because administrators can determine which devices are physically connected without relying only on manually maintained documentation. Junos devices can use operational commands to display discovered LLDP neighbors and their associated interfaces. LLDP operates at Layer 2 and does not establish routing relationships like OSPF or BGP. It is also separate from authentication protocols such as RADIUS.

Question 151:

Which technology is commonly used to assign a dedicated VLAN for IP phone traffic on an enterprise switch?

1. Guest VLAN
2. Voice VLAN
3. Management VLAN only
4. Native routing table

Correct Answer: 2

Explanation:

A voice VLAN provides a logical VLAN specifically intended for IP phone traffic. Separating voice traffic from ordinary data traffic allows administrators to apply appropriate security and quality-of-service policies. An IP phone can use the voice VLAN while a computer connected through the phone may use a separate data VLAN. Technologies such as LLDP-MED can assist with endpoint discovery and network-policy information, while CoS mechanisms can prioritize voice traffic. Voice VLANs are therefore an important component of enterprise IP telephony deployments. They do not replace routing tables or provide authentication by themselves, so additional security and network-control mechanisms may still be required.

Question 152:

Which technology can help an IP phone learn network policy information from a compatible switch?

1. LLDP-MED
2. BGP
3. OSPF
4. MPLS

Correct Answer: 1

Explanation:

LLDP-MED extends LLDP capabilities to provide additional information useful for media endpoints such as IP phones. One important use is communicating network policy information that can help an endpoint determine how its traffic should be handled. In an enterprise environment, this can simplify voice deployments by allowing supported phones to learn information from the network rather than relying entirely on manual configuration. LLDP-MED can work together with voice VLANs and PoE to support IP telephony deployments. It does not provide routing between networks or establish MPLS tunnels. Understanding LLDP-MED is especially useful when troubleshooting phone provisioning and voice VLAN behavior.

Question 153:

Which CoS mechanism can determine a packet’s forwarding class based on its DSCP value?

1. Scheduler
2. Classifier
3. Shaper
4. Drop profile

Correct Answer: 2

Explanation:

A CoS classifier can examine packet markings such as DSCP and use them to determine the appropriate forwarding class and packet loss priority. This process is known as classification and forms an important first step in differentiated traffic treatment. Once traffic has been classified, other CoS mechanisms can determine how it is queued, scheduled, shaped, or dropped during congestion. A scheduler controls transmission resources, while a shaper controls the rate at which traffic is transmitted. A drop profile influences packet-dropping behavior under congestion. Understanding classification is essential when troubleshooting why packets with different markings are receiving different forwarding treatment.

Question 154:

What is the primary purpose of a CoS drop profile?

1. To define packet-dropping behavior as congestion increases
2. To establish an OSPF adjacency
3. To assign a BGP router ID
4. To create an EVPN route

Correct Answer: 1

Explanation:

A CoS drop profile defines how packets may be dropped as queue congestion increases. It can be used to establish a relationship between queue occupancy or congestion conditions and the probability or behavior of packet loss. This allows network administrators to protect important traffic while allowing lower-priority traffic to be discarded when resources become constrained. Drop profiles are often considered together with packet loss priority, forwarding classes, queues, and schedulers. They are not routing-protocol mechanisms. Properly designed drop behavior can help maintain service quality for important applications during periods of congestion instead of treating every packet identically.

Question 155:

Which statement best describes a firewall filter in Junos?

1. It can classify or control packets according to configured match conditions and actions
2. It automatically establishes BGP sessions
3. It performs VXLAN encapsulation
4. It calculates OSPF SPF paths

Correct Answer: 1

Explanation:

A Junos firewall filter provides a flexible mechanism for examining packets and taking configured actions based on match conditions. Conditions can include characteristics such as source or destination addresses, protocols, ports, or other packet information. Actions may include accepting, discarding, counting, logging, or other supported processing. Firewall filters can be applied in different locations depending on the platform and design requirements, including interfaces and control-plane protection scenarios. They are distinct from routing policies, which primarily control route processing. Firewall filters are useful for traffic control and protection but do not establish routing protocol sessions or perform VXLAN encapsulation.

Question 156:

What is the primary purpose of control-plane protection using a firewall filter?

1. To protect the routing engine from unwanted or excessive traffic
2. To increase the number of VLAN IDs
3. To create VXLAN tunnels
4. To select BGP local preference automatically

Correct Answer: 1

Explanation:

Control-plane protection helps protect the routing engine from unwanted, malformed, or excessive traffic directed toward the device itself. A firewall filter can be used to permit required control-plane traffic while restricting traffic that should not reach routing or management processes. This can reduce the risk that excessive traffic consumes control-plane resources and affects routing stability. Careful design is important because blocking required protocol traffic can also disrupt network operations. Protocols such as BGP, OSPF, SSH, and management services may require explicit consideration when implementing control-plane filtering. The goal is to protect the device without unintentionally preventing legitimate control-plane communication.

Question 157:

Which authentication protocol is commonly used by 802.1X infrastructure to communicate authentication requests to a centralized authentication server?

1. EAPOL only
2. RADIUS
3. VXLAN
4. OSPF

Correct Answer: 2

Explanation:

RADIUS is commonly used between an access device acting as an authenticator and a centralized authentication server in 802.1X deployments. The endpoint and access device use the appropriate 802.1X/EAP mechanisms for authentication exchange, while the network device communicates with the authentication server using RADIUS. This separation allows centralized authentication and authorization policies to be managed through dedicated servers. Depending on the authentication result, the access device can apply different network-access policies. Understanding the roles of the supplicant, authenticator, and authentication server is important when troubleshooting 802.1X. RADIUS itself is not a Layer 2 routing or tunneling protocol.

Question 158:

What is a key advantage of MAC-based authentication for enterprise endpoints?

1. It can provide network access control for devices that may not support 802.1X
2. It replaces all routing protocols
3. It automatically encrypts Ethernet frames
4. It eliminates the need for VLANs

Correct Answer: 1

Explanation:

MAC-based authentication can provide access control for devices that do not support traditional 802.1X authentication. Examples can include printers, specialized equipment, IoT devices, and other endpoints with limited authentication capabilities. The access device uses the endpoint’s MAC address as an identity and communicates with a RADIUS server or other configured authentication system. Based on the authentication result, the device can apply an appropriate access policy. MAC authentication is generally less strong than user- or certificate-based authentication because a MAC address can potentially be spoofed, so it should be deployed with appropriate security controls. It is nevertheless useful for managing diverse enterprise endpoint types.

Question 159:

Which EVPN concept allows multiple PE devices to provide redundant connectivity to the same customer Ethernet segment?

1. EVPN multihoming
2. OSPF stub area
3. BGP route reflection
4. RADIUS fallback

Correct Answer: 1

Explanation:

EVPN multihoming allows multiple provider edge devices to connect to the same customer-side Ethernet segment and provide redundancy. This architecture can improve availability because traffic can continue through another PE if one PE or its connectivity fails. EVPN uses Ethernet Segment information, ESI, and related control-plane mechanisms to coordinate forwarding across the multihomed segment. Designated Forwarder election also plays an important role in controlling certain BUM traffic toward the customer segment. Multihoming is therefore a major EVPN capability for resilient Layer 2 connectivity. It is different from BGP route reflection, which addresses iBGP scalability rather than Ethernet-segment redundancy.

Question 160:

Which Junos operational command can be used to verify MAC addresses learned by an Ethernet switching device?

1. show route
2. show bgp summary
3. show ethernet-switching table
4. show ospf neighbor

Correct Answer: 3

Explanation:

The show ethernet-switching table command displays MAC addresses learned by the Ethernet switching system. The output can help administrators determine which MAC addresses have been learned and on which interfaces or logical switching contexts they are associated. This is especially useful when troubleshooting Layer 2 connectivity, unexpected flooding, or endpoint movement. If a MAC address is not present when expected, the administrator can investigate issues involving VLAN configuration, interface state, learning behavior, or traffic flow. The command is specifically focused on Ethernet switching information, whereas show route displays Layer 3 routing information and BGP or OSPF commands provide protocol-specific routing details.