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Question 161

Which routing protocol uses a link-state database?

1. RIP
2. OSPF
3. BGP
4. PIM

Correct Answer: 2

Explanation:

OSPF is a link-state routing protocol that maintains a database describing the network topology within its routing domain. Routers exchange link-state information with neighbors and use that information to construct a consistent view of the topology. The Shortest Path First algorithm then calculates suitable paths based on the information stored in the link-state database. RIP uses a distance-vector approach, BGP uses path attributes and policy, and PIM is designed for multicast routing. Therefore, OSPF is the correct answer because maintaining and processing a link-state database is fundamental to its routing operation.

Question 162

Which BGP attribute contains the preferred next-hop address?

1. Origin
2. Community
3. Next Hop
4. MED

Correct Answer: 3

Explanation:

The BGP Next Hop attribute identifies the IP address that should be used as the next routing step toward a destination prefix. Receiving BGP speakers use this information when determining how traffic should reach the advertised network. Next-hop processing can vary depending on whether routes are exchanged through internal or external BGP sessions and according to configured policies. Origin identifies how a route entered BGP, Community provides policy classification, and MED can influence entry-point selection. Therefore, Next Hop is the correct answer because it directly identifies the address associated with forwarding toward the advertised destination.

Question 163

Which Junos command displays the routing table briefly?

1. show route brief
2. show route summary
3. show route terse
4. show routing overview

Correct Answer: 3

Explanation:

The Junos show route terse command provides a concise view of routing-table information. It is useful when administrators need to quickly inspect route entries without the extensive detail produced by more comprehensive routing commands. The output can help identify destination prefixes, protocol information, preference values, and other basic route attributes in a compact format. Other commands may display more specialized information or may not be valid Junos operational commands. Therefore, show route terse is the correct answer because it is the standard Junos command for obtaining a compact routing-table view.

Question 164

Which protocol exchanges link-state information between routers?

1. FTP
2. OSPF
3. RADIUS
4. DHCP

Correct Answer: 2

Explanation:

OSPF exchanges link-state information between participating routers so that each router can construct an understanding of the network topology. This information is distributed through Link-State Advertisements and maintained in the OSPF link-state database. Once the database is sufficiently synchronized, routers use SPF calculations to determine appropriate paths toward destinations. FTP provides file transfer, RADIUS supports centralized authentication, and DHCP supplies network configuration information. Therefore, OSPF is the correct answer because link-state information exchange is central to its operation as an interior gateway routing protocol.

Question 165

Which mechanism reduces repeated route advertisements during instability?

1. Route dampening
2. Prefix delegation
3. Address translation
4. Interface polling

Correct Answer: 1

Explanation:

BGP route dampening is designed to reduce the impact of unstable routes that repeatedly change state. A route that frequently flaps can generate repeated advertisements and withdrawals, consuming processing resources and potentially affecting routing stability. Dampening assigns penalties to unstable routes and can temporarily suppress routes that exceed configured thresholds. The mechanism allows routes to become usable again after the accumulated penalty decreases sufficiently. Prefix delegation distributes address blocks, address translation modifies address information, and interface polling monitors interfaces. Therefore, route dampening is the correct answer because it specifically addresses repeated route instability and excessive route changes.

Question 166

Which IPv4 address range is reserved for private networks?

1. 8.8.8.0/24
2. 172.16.0.0/12
3. 1.1.1.0/24
4. 198.51.100.0/24

Correct Answer: 2

Explanation:

The IPv4 block 172.16.0.0/12 is one of the standardized private address ranges defined for internal network use. Private addresses are not globally routable on the public Internet and are commonly used inside organizational networks. Other private ranges include 10.0.0.0/8 and 192.168.0.0/16. The 8.8.8.0/24 and 1.1.1.0/24 ranges are associated with publicly reachable services, while 198.51.100.0/24 is reserved for documentation and examples. Therefore, 172.16.0.0/12 is the correct answer because it belongs to the recognized private IPv4 address space.

Question 167

Which protocol carries authentication requests using UDP?

1. RADIUS
2. OSPF
3. LDP
4. NTP

Correct Answer: 1

Explanation:

RADIUS traditionally uses UDP for communication between network access devices and the RADIUS authentication server. Common RADIUS functions include authentication, authorization, and accounting. The protocol is widely used in network-access environments where centralized identity validation is required. OSPF uses IP protocol mechanisms rather than UDP transport, LDP uses TCP and UDP depending on its discovery and session functions, while NTP uses UDP for time synchronization. Therefore, RADIUS is the correct answer because its traditional authentication and accounting exchanges are transported using UDP.

Question 168

Which Junos object represents a logical routing instance?

1. Routing instance
2. Firewall term
3. Interface family
4. Chassis cluster

Correct Answer: 1

Explanation:

A Junos routing instance represents a logical routing environment that can maintain its own interfaces, routing information, and forwarding behavior according to the configured instance type. Routing instances are useful for separating networks, implementing VPN services, and supporting specialized forwarding requirements on the same physical device. A firewall term defines packet-filtering conditions and actions, an interface family identifies protocol-family configuration, and a chassis cluster provides device-level redundancy on supported platforms. Therefore, routing instance is the correct answer because it directly represents an independent logical routing context within Junos.

Question 169

Which BGP message requests termination of an established session?

1. UPDATE
2. KEEPALIVE
3. NOTIFICATION
4. OPEN

Correct Answer: 3

Explanation:

The BGP NOTIFICATION message is used to report errors and terminate a BGP session when protocol conditions require the connection to close. It includes information identifying the error category and, where applicable, a more specific error subcode. After sending a NOTIFICATION, the BGP session is normally terminated. OPEN messages establish BGP session parameters, UPDATE messages exchange routing information, and KEEPALIVE messages maintain session liveness. Therefore, NOTIFICATION is the correct answer because it communicates a BGP error condition and is used when closing the affected session.

Question 170

Which Junos feature applies packet filtering rules to interfaces?

1. Firewall filter
2. Routing instance
3. Policy statement
4. Scheduler map

Correct Answer: 1

Explanation:

A Junos firewall filter applies packet-processing rules to traffic entering or leaving an interface, depending on how the filter is configured and applied. Filter terms can match characteristics such as source addresses, destination addresses, protocols, ports, or other packet fields and then perform actions such as accepting, discarding, counting, or marking traffic. Routing instances separate forwarding environments, policy statements control routing decisions, and scheduler maps relate to traffic scheduling. Therefore, firewall filter is the correct answer because it is specifically designed to inspect packets and apply configured filtering actions.

Question 171

Which IPv6 feature replaces traditional broadcast communication?

1. Anycast
2. Multicast
3. Unicast
4. Loopback

Correct Answer: 2

Explanation:

IPv6 does not use traditional broadcast addressing. Instead, multicast is used for many functions that previously relied on IPv4 broadcast communication. For example, Neighbor Discovery uses specific multicast groups to communicate efficiently with relevant devices on the local link. Anycast identifies multiple possible destinations while directing traffic toward an appropriate instance, and unicast identifies an individual interface. Loopback is used for communication within the local host. Therefore, multicast is the correct answer because IPv6 uses multicast addressing for functions that commonly required broadcast in IPv4.

Question 172

Which technology provides centralized log collection from devices?

1. Syslog
2. VRRP
3. LACP
4. ARP

Correct Answer: 1

Explanation:

Syslog provides a standardized method for generating, transporting, and collecting system messages from network devices. Organizations can configure devices to send event messages to centralized logging servers, allowing administrators to review operational activity across many systems from one location. Centralized logs are valuable for troubleshooting, auditing, event correlation, and operational monitoring. VRRP provides gateway redundancy, LACP manages aggregated links, and ARP resolves IPv4 addresses to MAC addresses. Therefore, Syslog is the correct answer because it is specifically designed to transport and collect device-generated log messages for centralized analysis.

Question 173

Which routing method selects paths using administrative policy?

1. BGP
2. ARP
3. STP
4. DHCP

Correct Answer: 1

Explanation:

BGP provides extensive policy-based routing capabilities through attributes, routing policies, and controlled route advertisement. Administrators can influence which routes are accepted, rejected, preferred, modified, or advertised to particular peers. This makes BGP particularly suitable for environments where routing decisions depend on organizational policy rather than simply selecting a shortest path based on a single metric. ARP performs address resolution, STP controls Layer 2 topology, and DHCP provides host configuration. Therefore, BGP is the correct answer because policy-driven route selection is one of its defining operational characteristics.

Question 174

Which MPLS table stores label forwarding information?

1. mpls.0
2. inet.0
3. inet6.0
4. iso.0

Correct Answer: 1

Explanation:

The Junos mpls.0 table is associated with MPLS forwarding information. It contains information used when processing MPLS labels and forwarding labeled traffic through the device. MPLS forwarding differs from ordinary IPv4 or IPv6 forwarding because the packet’s label information is used to determine the appropriate forwarding operation. The inet.0 table is associated with IPv4 unicast routing, inet6.0 with IPv6 routing, and iso.0 is associated with ISO-related routing information. Therefore, mpls.0 is the correct answer for MPLS forwarding information.

Question 175

Which mechanism controls the order of BGP route advertisements?

1. Update generation
2. Route policy
3. MAC learning
4. Neighbor solicitation

Correct Answer: 2

Explanation:

BGP routing policies can control which routes are accepted, modified, or advertised to particular peers. By applying policies at import and export points, administrators can influence the routing information exchanged between BGP speakers. Policies can match prefixes, communities, autonomous-system information, and other attributes, then perform actions that modify or control route handling. MAC learning belongs to Ethernet switching, while neighbor solicitation belongs to IPv6 Neighbor Discovery. Therefore, route policy is the correct answer because policy controls how BGP routing information is processed and advertised according to administrative requirements.

Question 176

Which interface state indicates administrative shutdown?

1. Down
2. Disabled
3. Dormant
4. Testing

Correct Answer: 2

Explanation:

A disabled administrative state indicates that an interface has been intentionally deactivated through configuration rather than simply becoming unavailable because of a physical or operational failure. Administrators may disable an interface when it is unused, during maintenance, or when troubleshooting a particular connection. The exact display terminology can vary according to the command and platform context, but the concept of administrative disabling is distinct from an interface failing because of physical conditions. Therefore, Disabled is the correct answer because it represents intentional administrative deactivation of the interface.

Question 177

Which protocol provides rapid detection of path failures?

1. BFD
2. DNS
3. FTP
4. LDAP

Correct Answer: 1

Explanation:

Bidirectional Forwarding Detection, or BFD, provides rapid detection of failures along a forwarding path. BFD establishes sessions between participating devices and exchanges control packets at configured intervals. If expected packets are no longer received within the detection interval, the session can be declared down. Routing protocols or other dependent mechanisms can then react to the detected failure. DNS provides name resolution, FTP transfers files, and LDAP provides directory services. Therefore, BFD is the correct answer because its primary purpose is fast detection of forwarding-path failures.

Question 178

Which BGP attribute categorizes routes for policy processing?

1. Community
2. Router ID
3. Hold Timer
4. TCP Window

Correct Answer: 1

Explanation:

The BGP Community attribute provides a mechanism for grouping or tagging routes according to administrative policy. Communities can be assigned to routes and then matched by routing policies to determine actions such as accepting, rejecting, modifying, or advertising routes differently. This makes communities useful for simplifying large-scale policy implementation. Router ID identifies a BGP speaker, the Hold Timer controls session liveness, and TCP Window is a transport-level concept rather than a BGP routing attribute. Therefore, Community is the correct answer because it provides policy-oriented classification of BGP routes.

Question 179

Which protocol transports MPLS labels across provider networks?

1. LDP
2. DHCP
3. RADIUS
4. SNMP

Correct Answer: 1

Explanation:

LDP is used in many MPLS deployments to distribute label bindings between routers. These bindings associate forwarding equivalence classes with labels, allowing participating routers to establish label-switched forwarding along paths derived from the underlying routing topology. LDP therefore helps create the control-plane information required for ordinary MPLS label switching. DHCP provides host configuration, RADIUS handles centralized authentication, and SNMP provides network-management information. Therefore, LDP is the correct answer because it distributes the label information needed to establish MPLS forwarding behavior across participating provider routers.

Question 180

Which IPv4 protocol reports network-layer delivery errors?

1. ICMP
2. ARP
3. DHCP
4. FTP

Correct Answer: 1

Explanation:

Internet Control Message Protocol, or ICMP, provides control and error-reporting messages for IPv4 networks. Network devices can generate ICMP messages when certain delivery conditions occur, such as unreachable destinations or expired packet lifetimes. Diagnostic tools can also use ICMP messages to test connectivity and measure response behavior. ARP performs local address resolution, DHCP supplies configuration information, and FTP transfers files. Therefore, ICMP is the correct answer because it provides standardized network-layer control and error-reporting functions within IPv4 environments.