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Question 41

Which protocol uses link-state advertisements for topology exchange?

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

Correct Answer: 3

Explanation:

OSPF uses Link-State Advertisements, commonly called LSAs, to distribute information about network topology among participating routers. These advertisements allow routers to build their link-state databases and maintain a consistent representation of the OSPF topology. After collecting the relevant LSAs, each router runs the Shortest Path First algorithm to calculate routes. RIP uses periodic distance-vector updates, BGP exchanges path information between autonomous systems, and DHCP provides host configuration parameters. Therefore, OSPF is the correct choice because LSAs are a fundamental part of how OSPF routers exchange and maintain topology information throughout an OSPF routing domain.

Question 42

Which protocol carries IPv6 routing information internally?

1. IS-IS
2. ARP
3. BFD
4. LACP

Correct Answer: 1

Explanation:

IS-IS can carry IPv6 routing information within an autonomous system and is widely used in service-provider environments. It supports IPv6 through extensions that allow routers to advertise IPv6 reachability while maintaining the protocol’s link-state operation. This makes IS-IS suitable for networks operating both IPv4 and IPv6. ARP is associated with IPv4 address resolution and does not provide IPv6 routing. BFD provides rapid failure detection, while LACP manages link aggregation. Therefore, IS-IS is the correct answer because it can distribute IPv6 reachability information as part of an internal service-provider routing architecture.

Question 43

What identifies a unique BGP routing process?

1. VLAN ID
2. Router ID
3. MPLS label
4. Interface index

Correct Answer: 2

Explanation:

A BGP Router ID uniquely identifies a BGP speaker within its routing environment. It is represented as a 32-bit value and is commonly displayed in IPv4 address notation. The Router ID is important for identifying the BGP process and participating in route-selection and protocol operations. A VLAN ID identifies a Layer 2 broadcast domain, an MPLS label identifies forwarding treatment, and an interface index identifies a particular interface. These values serve different purposes and do not uniquely identify the BGP process. Therefore, Router ID is the correct answer for identifying a BGP speaker within the routing system.

Question 44

Which protocol prevents Layer 2 switching loops?

1. BFD
2. STP
3. LDP
4. PIM

Correct Answer: 2

Explanation:

Spanning Tree Protocol, or STP, prevents Layer 2 switching loops by creating a loop-free logical topology among interconnected switches. STP identifies redundant paths and places selected interfaces into a blocking state while maintaining alternative paths for redundancy. If the active topology changes, STP can transition appropriate interfaces to restore connectivity without creating a persistent Layer 2 loop. BFD detects forwarding failures, LDP distributes MPLS labels, and PIM manages multicast routing. Therefore, STP is the correct answer because its fundamental purpose is preventing Layer 2 loops caused by redundant Ethernet connections.

Question 45

Which BGP attribute identifies route origin type?

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

Correct Answer: 1

Explanation:

The BGP Origin attribute indicates how a route was introduced into BGP. It has values representing different origins, including IGP, EGP, and incomplete. During BGP path selection, the origin type can influence which route is preferred when other relevant attributes are comparable. Next Hop identifies the address used to reach a destination, while MED can influence entry-point selection between neighboring autonomous systems. Community values provide tags that can be used for routing-policy decisions. Therefore, Origin is the correct answer because it specifically describes the source or method through which a prefix entered the BGP routing system.

Question 46

Which technology combines multiple physical Ethernet links?

1. VRF
2. LACP
3. BGP
4. PIM

Correct Answer: 2

Explanation:

Link Aggregation Control Protocol, or LACP, allows multiple physical Ethernet links to operate together as a logical aggregated connection. This can provide increased available bandwidth and redundancy between compatible network devices. LACP negotiates and maintains the aggregation relationship between participating systems. VRF separates routing tables, BGP exchanges routing information, and PIM handles multicast routing. These technologies do not combine physical Ethernet interfaces into a single logical link. Therefore, LACP is the correct answer because it provides standardized control for establishing and maintaining link aggregation between network devices.

Question 47

Which Junos table stores MPLS forwarding information?

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

Correct Answer: 3

Explanation:

The mpls.0 routing table in Junos is associated with MPLS forwarding information. It contains information used when processing MPLS-labeled traffic and helps the device determine appropriate forwarding behavior for label-based packets. The inet.0 table is primarily associated with IPv4 unicast routing, while inet6.0 is associated with IPv6 routing. The iso.0 table relates to ISO protocol addressing and routing information. Understanding the purpose of these routing tables is useful when troubleshooting MPLS and IP forwarding. Therefore, mpls.0 is the correct choice for MPLS forwarding information.

Question 48

Which protocol provides IPv4 address resolution to MAC addresses?

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

Correct Answer: 2

Explanation:

Address Resolution Protocol, or ARP, maps an IPv4 address to the corresponding Layer 2 MAC address on a local network. When a device needs to send an IPv4 packet to a directly reachable destination but does not know the destination’s MAC address, it can use ARP to discover that information. DHCP provides network configuration parameters, NTP synchronizes clocks, and LLDP exchanges neighbor information. These protocols perform different functions and do not provide standard IPv4-to-MAC address resolution. Therefore, ARP is the correct answer because it connects IPv4 addressing information with the MAC address required for local Ethernet delivery.

Question 49

Which BGP attribute groups routes for policy application?

1. Community
2. Origin
3. AS Path
4. Next Hop

Correct Answer: 1

Explanation:

The BGP Community attribute allows routes to be logically grouped by assigning community values that can be referenced in routing policies. Administrators can use communities to identify particular categories of routes and apply consistent actions, such as modifying preferences, controlling advertisements, or influencing route handling. Origin identifies how a route entered BGP, AS Path records autonomous systems traversed by an advertisement, and Next Hop identifies the address used to reach the destination. Therefore, Community is the correct answer because it provides a flexible method for tagging and grouping BGP routes so that routing policies can process them efficiently.

Question 50

Which Junos command displays BGP neighbor sessions?

1. show bgp summary
2. show route forwarding-table
3. show interfaces terse
4. show chassis alarms

Correct Answer: 1

Explanation:

The Junos show bgp summary command provides a concise overview of BGP neighbor sessions. Its output can show peer addresses, autonomous-system information, session state, message counters, and received or accepted route information. This makes the command particularly useful for quickly determining whether BGP sessions are established and exchanging routing information. The forwarding-table command examines forwarding entries, show interfaces terse summarizes interface status, and show chassis alarms displays active system alarms. Therefore, show bgp summary is the appropriate command when an administrator needs a quick operational overview of BGP peer relationships.

Question 51

Which protocol establishes MPLS traffic-engineered signaling sessions?

1. RSVP-TE
2. LLDP
3. ARP
4. SNMP

Correct Answer: 1

Explanation:

RSVP-TE, or Resource Reservation Protocol with Traffic Engineering extensions, can establish and maintain signaling information for traffic-engineered MPLS paths. It allows network devices to communicate path and resource requirements and can support explicit path selection and bandwidth-related constraints. LLDP performs neighbor discovery, ARP resolves IPv4 addresses to MAC addresses, and SNMP provides network management functionality. These protocols do not establish MPLS traffic-engineered signaling sessions. Therefore, RSVP-TE is the correct answer because its extensions were designed specifically to support signaling and resource-related requirements for MPLS traffic-engineering paths.

Question 52

Which BGP feature carries additional route classification information?

1. MED
2. Communities
3. AS Path
4. Origin

Correct Answer: 2

Explanation:

BGP Communities provide additional classification information that can be attached to routes and used by routing policies. A community acts as a tag, allowing administrators to identify groups of prefixes without depending solely on their addresses. Policies can then use those tags to control advertisements, modify route attributes, or apply other routing actions. MED provides information related to preferred entry points, AS Path records autonomous systems traversed by a route, and Origin indicates how the route entered BGP. Therefore, Communities are the correct answer because they provide a flexible tagging mechanism for classifying and managing groups of BGP routes.

Question 53

Which protocol calculates shortest paths using link costs?

1. OSPF
2. BGP
3. LACP
4. DHCP

Correct Answer: 1

Explanation:

OSPF calculates shortest paths using the link-state information maintained in its database and the configured cost associated with network links. Each router constructs a topology view from received LSAs and then runs the Shortest Path First algorithm to determine the best paths. This approach allows OSPF to respond to topology changes and calculate routes based on the network’s link costs. BGP uses multiple path attributes, LACP manages aggregated Ethernet links, and DHCP provides host configuration information. Therefore, OSPF is the correct answer because its SPF calculations rely directly on link-state topology information and associated path costs.

Question 54

Which MPLS operation adds a label to packets?

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

Correct Answer: 3

Explanation:

The MPLS push operation adds a label to the packet’s existing label stack. This can occur when a packet enters an MPLS domain or when an additional service-related label is required. Adding labels allows packets to carry multiple forwarding contexts and supports architectures such as MPLS VPNs. Pop performs the opposite action by removing the top label, while swap replaces an existing top label with another label. Remove is not the standard name for an MPLS label operation. Therefore, push is the correct answer because it specifically describes adding an MPLS label to a packet.

Question 55

Which routing protocol supports hierarchical OSPF areas?

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

Correct Answer: 2

Explanation:

OSPF supports hierarchical routing through the use of areas. This design allows large OSPF networks to be divided into logical sections, reducing the amount of topology information that must be maintained and processed across the entire routing domain. Area 0, known as the backbone area, provides the central connection between other OSPF areas in a conventional hierarchical design. RIP does not use OSPF-style areas, BGP uses autonomous-system-based routing policies, and PIM is designed for multicast forwarding. Therefore, OSPF is the correct answer because hierarchical area architecture is a fundamental feature of the protocol.

Question 56

Which Junos command shows active system alarms?

1. show system alarms
2. show route receive-protocol
3. show interfaces descriptions
4. show protocols bgp

Correct Answer: 1

Explanation:

The Junos show system alarms command displays active system-level alarms reported by the device. These alarms can provide important indications of hardware, environmental, or operational conditions requiring administrator attention. Reviewing system alarms is useful when diagnosing unexpected behavior or checking the overall health of a Junos device. The other commands focus on different areas: route-receive information examines routing protocol information, interface descriptions provide interface-related details, and protocol configuration displays configured routing statements. Therefore, show system alarms is the appropriate command when the objective is to identify currently active system alarms.

Question 57

Which BGP attribute records the route’s originating autonomous system?

1. MED
2. AS Path
3. Local Preference
4. Community

Correct Answer: 2

Explanation:

The AS Path attribute records the sequence of autonomous systems associated with a BGP route advertisement. The first autonomous-system number in the relevant path represents the originating AS from which the external route was introduced into the path sequence. As the route crosses additional autonomous systems, their numbers are added to the path. This attribute also supports loop prevention because routers can reject routes containing their own AS number. MED influences interdomain entry-point selection, Local Preference influences outbound routing within an AS, and Community provides route tagging. Therefore, AS Path is the correct attribute for identifying autonomous-system path information.

Question 58

Which protocol detects unidirectional forwarding failures quickly?

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

Correct Answer: 1

Explanation:

BFD is designed to detect forwarding failures rapidly between network devices, including situations where bidirectional communication is no longer functioning correctly. Its control sessions exchange periodic packets and use configured detection intervals to identify failures quickly. When a failure is detected, associated routing protocols can react and reconverge without waiting for their normal, potentially longer timers. NTP handles time synchronization, LLDP provides neighbor discovery, and DHCP provides network configuration parameters. Therefore, BFD is the correct answer because it specifically provides fast failure detection for forwarding paths and can improve network convergence when a connectivity problem occurs.

Question 59

Which technology provides Layer 3 customer VPN isolation?

1. MPLS L3VPN
2. STP
3. LACP
4. LLDP

Correct Answer: 1

Explanation:

MPLS Layer 3 VPN technology provides logical separation between customer routing environments across a shared service-provider infrastructure. Customer routes are maintained in separate VRFs, while MPLS labels help transport traffic through the provider network toward the appropriate customer context. This architecture allows different customers to maintain independent routing information and can support overlapping address spaces. STP is used to prevent Layer 2 loops, LACP provides link aggregation, and LLDP supports neighbor discovery. Therefore, MPLS L3VPN is the correct answer because it is specifically designed to deliver isolated Layer 3 VPN services across a provider MPLS network.

Question 60

Which protocol provides centralized network device management data?

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

Correct Answer: 1

Explanation:

SNMP, or Simple Network Management Protocol, provides a standardized method for collecting and managing operational information from network devices. A network management system can query supported management objects to retrieve statistics, status information, and other operational data. SNMP can also support notifications that alert management systems about selected events. OSPF handles internal routing, RSVP provides signaling capabilities, and BFD detects forwarding failures. These protocols therefore have different operational purposes. SNMP is the correct answer because it is specifically designed to exchange management information between network devices and centralized monitoring or management systems.