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Question 1

Which protocol is commonly used as a link-state IGP?

1. OSPF
2. BGP
3. LDP
4. RSVP

Correct Answer: 1

Explanation:

OSPF is a link-state Interior Gateway Protocol used to exchange routing information within an autonomous system. It allows routers to maintain a detailed database describing the network topology. Each router independently runs the Shortest Path First algorithm against this database to calculate suitable routes. OSPF also supports hierarchical designs through areas, helping improve scalability in larger networks. BGP is primarily used for interdomain routing, while LDP distributes MPLS labels. RSVP provides signaling functions for resource reservation and traffic engineering. Therefore, OSPF is the correct choice because it specifically provides link-state routing capabilities within an autonomous system.

Question 2

Which protocol exchanges routes between different autonomous systems?

1. OSPF
2. BGP
3. IS-IS
4. RIP

Correct Answer: 2

Explanation:

BGP, or Border Gateway Protocol, is designed to exchange network reachability information between different autonomous systems. It is the principal interdomain routing protocol used across large service-provider and Internet environments. BGP makes routing decisions using attributes such as AS Path, Local Preference, MED, and Next Hop, allowing administrators to apply detailed routing policies. OSPF and IS-IS are interior gateway protocols normally used within an autonomous system, while RIP is another interior routing protocol with simpler capabilities and limited scalability. Therefore, BGP is the correct answer because its primary purpose is exchanging routing information across autonomous-system boundaries.

Question 3

Which protocol distributes labels across an MPLS network?

1. RSVP
2. BFD
3. LDP
4. SNMP

Correct Answer: 3

Explanation:

LDP, or Label Distribution Protocol, is used to distribute MPLS label bindings between routers. It works with the underlying routing topology to establish label-switched forwarding paths through an MPLS network. Routers exchange label information so packets can be forwarded using labels rather than performing a complete IP lookup at every MPLS hop. RSVP can provide signaling for specific traffic-engineering functions, while BFD focuses on rapid failure detection. SNMP is mainly used for network monitoring and management. Therefore, LDP is the correct answer because it specifically handles the distribution of label information required for conventional MPLS forwarding.

Question 4

Which routing protocol uses the shortest path first algorithm?

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

Correct Answer: 4

Explanation:

OSPF uses the Shortest Path First algorithm to calculate routes based on its link-state database. Each participating router maintains information about network links and their associated costs. After receiving and processing link-state advertisements, the router builds a topology database and runs SPF to determine the shortest available paths. BGP uses a path-selection process based on multiple attributes rather than SPF. LDP distributes MPLS labels and does not calculate the IP topology itself. RIP uses a distance-vector approach based on hop count. Therefore, OSPF is the protocol that directly uses the Shortest Path First algorithm.

Question 5

What does the BGP AS Path attribute identify?

1. Autonomous systems traversed by a route
2. Interface bandwidth available for forwarding
3. MPLS labels assigned to packets
4. Physical neighbors connected through Ethernet

Correct Answer: 1

Explanation:

The BGP AS Path attribute identifies the sequence of autonomous systems through which a route advertisement has traveled. Each AS that propagates an external BGP route normally adds its own autonomous-system number to the path. This information is important for both routing decisions and loop prevention. If a BGP router detects its own AS number in the received path, it can reject the route to avoid creating a routing loop. Interface bandwidth, MPLS labels, and physical Ethernet neighbors are represented through different mechanisms. Therefore, the AS Path attribute specifically describes the autonomous systems associated with a route advertisement.

Question 6

Which BGP attribute influences outbound traffic path selection?

1. MED
2. Local Preference
3. Origin
4. Atomic Aggregate

Correct Answer: 2

Explanation:

Local Preference is a BGP attribute used to influence outbound traffic decisions within an autonomous system. When multiple external routes are available, a higher Local Preference value is generally preferred by BGP. Because it is distributed within the local autonomous system, administrators can use it to establish which exit path should normally carry outbound traffic. MED serves a different purpose by providing information that can influence how another autonomous system enters the advertising network. Origin identifies how a route entered BGP, while Atomic Aggregate relates to route aggregation. Therefore, Local Preference is correct for controlling outbound path selection.

Question 7

Which mechanism provides independent routing tables for customers?

1. Route reflector
2. Label stack
3. VRF
4. Link aggregation

Correct Answer: 3

Explanation:

A Virtual Routing and Forwarding instance, or VRF, provides an independent routing table and forwarding context. Service providers commonly use VRFs to separate customer routing information within the same physical infrastructure. This separation allows different customers to use overlapping IP address ranges without their routes interfering with one another. A route reflector is used to simplify internal BGP route distribution. A label stack belongs to MPLS forwarding, while link aggregation combines multiple physical interfaces into a logical connection. Therefore, VRF is the correct mechanism because it specifically provides separate routing and forwarding environments for individual customers or logical network contexts.

Question 8

Which protocol rapidly detects forwarding path failures?

1. LLDP
2. ARP
3. BFD
4. NTP

Correct Answer: 3

Explanation:

BFD, or Bidirectional Forwarding Detection, provides rapid detection of failures along forwarding paths between network devices. It is designed to operate with relatively low overhead and can notify routing protocols when connectivity between neighbors is lost. This allows routing systems to react faster than they might when relying only on conventional protocol timers. LLDP is used to discover directly connected devices, ARP resolves IPv4 addresses to Layer 2 addresses, and NTP synchronizes clocks. Therefore, BFD is the correct answer because its primary purpose is quickly identifying forwarding-path failures and helping connected protocols respond to those failures.

Question 9

Which MPLS operation replaces one label with another?

1. Push
2. Pop
3. Swap
4. Peek

Correct Answer: 3

Explanation:

An MPLS swap operation replaces the existing top label with another label while forwarding the packet toward the next hop. This is a fundamental operation performed by transit Label Switching Routers within an MPLS network. The incoming label determines the forwarding action, and the router substitutes the appropriate outgoing label before transmitting the packet. Push adds a new label to the stack, while pop removes the top label. Peek is not a standard MPLS forwarding operation. Therefore, swap is the correct answer because it specifically describes replacing an incoming MPLS label with a different outgoing label.

Question 10

Which protocol discovers directly connected network devices?

1. LLDP
2. BGP
3. LDP
4. PIM

Correct Answer: 1

Explanation:

LLDP, or Link Layer Discovery Protocol, enables network devices to advertise identification and capability information to directly connected neighbors. A Junos device can use LLDP information to determine details about neighboring equipment and connected interfaces. This can be particularly useful during network documentation, topology verification, and troubleshooting. BGP exchanges routing information between autonomous-system peers, while LDP distributes MPLS label bindings. PIM is used for multicast routing rather than general Layer 2 neighbor discovery. Therefore, LLDP is the correct choice because it was specifically designed to allow directly connected network devices to discover and identify one another.

Question 11

Which Junos command displays the routing table information?

1. show interfaces
2. show route
3. show chassis hardware
4. show system users

Correct Answer: 2

Explanation:

The Junos show route command is used to display routing information from the device’s routing tables. It can provide details about destinations, next hops, routing protocols, route preferences, and active routes. Administrators commonly use this command during routing verification and troubleshooting to determine how a destination is being reached. The show interfaces command focuses on interface information and statistics. show chassis hardware displays hardware components, while show system users provides information about users currently connected to the device. Therefore, show route is the correct command for examining routing-table information on a Junos device.

Question 12

Which BGP message establishes initial session parameters?

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

Correct Answer: 4

Explanation:

The BGP OPEN message establishes the initial parameters required for a BGP session after the underlying TCP connection has been created. It contains information such as the BGP version, autonomous system number, hold time, and BGP identifier. Once both peers successfully exchange and accept their OPEN messages, they can proceed with normal BGP operations. UPDATE messages advertise or withdraw routing information, KEEPALIVE messages maintain an established relationship, and NOTIFICATION messages communicate errors that can cause a session to terminate. Therefore, OPEN is the correct answer because it is specifically responsible for negotiating the initial BGP session parameters between neighboring peers.

Question 13

Which BGP message carries route advertisements and withdrawals?

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

Correct Answer: 3

Explanation:

BGP UPDATE messages carry routing information between established BGP peers. An UPDATE can advertise reachable network prefixes together with relevant path attributes, or it can withdraw routes that are no longer available. This makes the UPDATE message central to exchanging and maintaining BGP routing information. OPEN messages establish session parameters, KEEPALIVE messages maintain an established relationship, and NOTIFICATION messages communicate errors that can cause a session to terminate. Therefore, UPDATE is the correct answer because it is the BGP message type specifically responsible for announcing reachable routes and withdrawing previously advertised destinations.

Question 14

Which routing protocol is widely deployed in provider core networks?

1. IS-IS
2. RIPv1
3. EGP
4. ODR

Correct Answer: 1

Explanation:

IS-IS is a link-state Interior Gateway Protocol widely used in service-provider core networks. It provides scalable routing within an autonomous system and supports hierarchical network designs through its Level 1 and Level 2 structure. Service providers often select IS-IS because it is well suited to large routing domains and can efficiently maintain topology information. RIPv1 is an older distance-vector protocol with significant limitations for modern provider networks. EGP is an obsolete exterior gateway protocol, while ODR is not a comparable provider-core IGP. Therefore, IS-IS is the appropriate answer for a widely deployed provider-core routing protocol.

Question 15

Which MPLS structure permits multiple labels simultaneously?

1. Route table
2. Label stack
3. ARP cache
4. Forwarding queue

Correct Answer: 2

Explanation:

An MPLS label stack allows multiple labels to be carried simultaneously within a packet. Each label can represent a different forwarding context or service function. For example, one label may identify a transport path while another identifies a particular VPN forwarding context. As packets travel through an MPLS network, routers can push additional labels, swap the top label, or remove labels when they are no longer required. A routing table contains network reachability information, an ARP cache stores address mappings, and a forwarding queue manages packets awaiting transmission. Therefore, the label stack is the structure that supports multiple MPLS labels.

Question 16

Which BGP feature simplifies large iBGP network designs?

1. Route reflection
2. Route poisoning
3. Split horizon
4. Broadcast forwarding

Correct Answer: 1

Explanation:

BGP route reflection simplifies large internal BGP deployments by reducing the need for every iBGP router to establish a direct session with every other iBGP router. A route reflector receives routes from its clients and can reflect appropriate routes to other clients. This significantly reduces the number of required BGP sessions and makes larger networks easier to operate. Route poisoning and split horizon are concepts associated with other routing mechanisms and are not the standard solution for iBGP scaling. Broadcast forwarding does not address BGP session requirements. Therefore, route reflection is the correct feature for simplifying large iBGP designs.

Question 17

Which Junos command provides detailed interface statistics?

1. show route summary
2. show system commit
3. show interfaces extensive
4. show configuration protocols

Correct Answer: 3

Explanation:

The Junos show interfaces extensive command provides detailed operational information about network interfaces. Its output can include physical and logical interface states, traffic counters, packet statistics, error information, and other operational details useful for troubleshooting. This makes the command valuable when investigating connectivity problems, interface failures, or unexpected traffic behavior. show route summary focuses on routing-table statistics, while show system commit provides information about configuration commits. show configuration protocols displays configured protocol statements rather than detailed interface statistics. Therefore, show interfaces extensive is the correct command when comprehensive interface information is required.

Question 18

Which BGP attribute helps prevent autonomous-system routing loops?

1. MED
2. AS Path
3. Local Preference
4. Next Hop

Correct Answer: 2

Explanation:

The AS Path attribute helps prevent routing loops in BGP by recording the autonomous systems through which a route advertisement has passed. When a BGP router receives an advertisement, it examines the AS Path to determine whether its own autonomous-system number is already present. If its number appears, the router can reject the route because accepting it could create a routing loop. MED influences route selection between neighboring autonomous systems, while Local Preference influences outbound decisions within an autonomous system. Next Hop identifies the address used to reach the advertised destination. Therefore, AS Path provides the relevant loop-prevention mechanism.

Question 19

Which protocol synchronizes clocks across network devices?

1. SNMP
2. LLDP
3. NTP
4. DHCP

Correct Answer: 3

Explanation:

NTP, or Network Time Protocol, synchronizes system clocks across network-connected devices. Accurate time synchronization is important for service-provider environments because logs, troubleshooting records, authentication processes, and event correlation often depend on consistent timestamps. SNMP is primarily used for network monitoring and management. LLDP provides information about directly connected devices, while DHCP can provide network configuration such as IP addressing and other parameters to clients. None of these protocols has the primary purpose of maintaining synchronized system time. Therefore, NTP is the correct answer because it is specifically designed to coordinate clock information across network devices.

Question 20

Which Junos command enters configuration mode from operational mode?

1. commit
2. rollback
3. configure
4. exit

Correct Answer: 3

Explanation:

The Junos configure command moves the administrator from operational mode into configuration mode. Configuration mode is where users create, modify, or remove configuration statements on a Junos device. Changes are initially placed in the candidate configuration and normally require a commit operation before becoming active. The rollback command is used to return configuration changes toward a previous state, while exit leaves the current configuration context or mode. Therefore, configure is the correct command for entering configuration mode from operational mode. Understanding the distinction between operational and configuration modes is essential for effective Junos device administration.