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Question 341

Which OSPF LSA type is used by an ABR to advertise networks from one OSPF area into another area?

1. Type 5
2. Type 2
3. Type 3
4. Type 7

Correct Answer: 3

Explanation

OSPF Type 3 LSAs, also called Summary LSAs, are generated by Area Border Routers (ABRs) to advertise networks from one OSPF area into another. They allow routers in different areas to learn about inter-area destinations without requiring the complete link-state database of another area. Type 5 LSAs advertise external routes, Type 2 LSAs describe multiaccess networks, and Type 7 LSAs are used for external routes inside NSSA areas. Type 3 LSAs therefore play an important role in maintaining OSPF’s hierarchical architecture and controlling the scope of topology information between areas.

Question 342

Which OSPF LSA provides information about the location of an ASBR to routers in other areas?

1. Type 4
2. Type 1
3. Type 5
4. Type 2

Correct Answer: 1

Explanation

OSPF Type 4 LSAs, known as ASBR Summary LSAs, are generated by an ABR to provide reachability information toward an Autonomous System Boundary Router located in another OSPF area. This information allows routers in other areas to determine how to reach the ASBR that originates external routes. Type 1 LSAs describe routers within an area, Type 2 LSAs describe multiaccess networks, and Type 5 LSAs carry external route information. Type 4 is therefore specifically associated with locating an ASBR across an OSPF area boundary.

Question 343

Which OSPF network type normally elects a DR and BDR?

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

Correct Answer: 2

Explanation

OSPF broadcast network types, such as Ethernet, normally use a Designated Router (DR) and Backup Designated Router (BDR). The election reduces the number of full OSPF adjacencies required on a multiaccess segment and makes link-state flooding more efficient. Point-to-point networks do not require a DR or BDR because only two routers participate in the link. Loopback interfaces have different OSPF behavior, while point-to-multipoint networks generally do not use a DR election. Therefore, broadcast is the correct network type.

Question 344

Which OSPF configuration can prevent an interface from forming OSPF neighbor relationships while still allowing its connected network to be advertised?

1. Passive interface
2. Stub area
3. Route summarization
4. LSA filtering

Correct Answer: 1

Explanation

A passive OSPF interface does not send OSPF Hello packets and therefore does not form OSPF neighbor adjacencies through that interface. However, the connected network can still be advertised through OSPF, depending on the configuration. This is particularly useful for user-facing or infrastructure interfaces where routing advertisements are required but no OSPF neighbor should exist. Stub areas affect LSA behavior across an area, while summarization aggregates routes and LSA filtering controls information exchange. Therefore, passive interface is correct.

Question 345

Which IS-IS level is primarily responsible for routing within a single IS-IS area?

1. Level-2
2. Level-1
3. Level-3
4. Level-0

Correct Answer: 2

Explanation

IS-IS Level-1 routing is primarily responsible for routing within a single IS-IS area. Level-1 routers maintain information about destinations inside their local area and use Level-2 connectivity to reach destinations outside the area when necessary. Level-2 routing provides inter-area connectivity between Level-2 routers. IS-IS does not define standard Level-0 or Level-3 routing levels. This hierarchical model allows service-provider networks to scale while separating intra-area and inter-area topology information. Therefore, Level-1 is the correct answer.

Question 346

Which IS-IS level is responsible for providing connectivity between different IS-IS areas?

1. Level-2
2. Level-1
3. Level-0
4. Level-3

Correct Answer: 1

Explanation

IS-IS Level-2 routing provides connectivity between different IS-IS areas. Level-2 routers maintain the inter-area topology and form the backbone of the IS-IS routing domain. Level-1 routers focus on routing within their local areas and normally rely on Level-2 routers to reach destinations outside the local area. This hierarchical separation helps control the amount of topology information required by individual routers. Level-0 and Level-3 are not standard IS-IS routing levels. Therefore, Level-2 is correct.

Question 347

Which IS-IS role is commonly elected on a broadcast network to perform database synchronization functions?

1. Route Reflector
2. Designated Intermediate System
3. Area Border Router
4. Autonomous System Boundary Router

Correct Answer: 2

Explanation

The Designated Intermediate System (DIS) is elected on IS-IS broadcast networks. The DIS performs important functions for representing the multiaccess segment in the IS-IS link-state database and helps with database synchronization. Unlike OSPF, IS-IS does not elect a Backup DIS in the same way OSPF elects a BDR. A DIS can be replaced through a new election if required. Route Reflectors belong to BGP, while ABR and ASBR are OSPF terminology. Therefore, Designated Intermediate System is correct.

Question 348

Which BGP attribute is normally preferred when selecting between routes learned from different external BGP peers, assuming other higher-priority criteria are equal?

1. Highest MED
2. Lowest Local Preference
3. Shortest AS_PATH
4. Highest Router ID

Correct Answer: 3

Explanation

The AS_PATH length is an important BGP best-path criterion. When comparing otherwise suitable routes, BGP generally prefers the path with the shorter AS_PATH because it represents fewer autonomous-system hops. Local Preference is considered earlier and a higher value is normally preferred within an AS. MED can influence path selection but is considered later than several other attributes, and Router ID is used in later tie-breaking rather than as a primary path metric. Therefore, among the choices, the shortest AS_PATH is the correct answer.

Question 349

Which BGP attribute is normally preferred when comparing routes within the same autonomous system?

1. Lowest Local Preference
2. Highest Local Preference
3. Highest MED
4. Longest AS_PATH

Correct Answer: 2

Explanation

BGP normally prefers the route with the highest Local Preference value when comparing routes within an autonomous system. Local Preference communicates the preferred exit point for traffic leaving the AS and is propagated through iBGP. Because it is an important internal policy attribute, service providers frequently use it to influence outbound traffic paths. MED and AS_PATH are considered at different stages of BGP path selection, and a longer AS_PATH is generally less preferred. Therefore, the highest Local Preference is correct.

Question 350

Which BGP attribute is commonly used by one autonomous system to suggest a preferred entry point to another autonomous system?

1. MED
2. Weight
3. Router ID
4. Cluster List

Correct Answer: 1

Explanation

The Multi-Exit Discriminator (MED) is commonly used to communicate a preference for one entry point into an autonomous system when multiple links exist between neighboring autonomous systems. A lower MED is generally preferred when comparing routes from the same neighboring AS, subject to implementation and policy considerations. MED is not a mandatory global routing policy and operators may modify or ignore it. Weight is locally significant on some Cisco platforms, while Cluster List is associated with BGP route reflection. Therefore, MED is correct.

Question 351

Which BGP attribute is locally significant and is not normally propagated to other BGP routers?

1. Local Preference
2. Weight
3. MED
4. Community

Correct Answer: 2

Explanation

BGP Weight is a Cisco-specific attribute that is locally significant to a router. It can influence which path that particular router selects, with higher values generally preferred. Unlike Local Preference, Weight is not propagated through BGP to other routers. Local Preference is commonly shared within an autonomous system through iBGP, MED can be advertised between autonomous systems, and Communities can carry policy information across BGP domains. Therefore, Weight is the correct answer for an attribute that remains local to the router.

Question 352

Which BGP feature prevents an iBGP-learned route from normally being advertised to another iBGP neighbor?

1. iBGP split horizon
2. BGP Add-Path
3. Route Refresh
4. MED

Correct Answer: 1

Explanation

BGP follows an iBGP split-horizon rule: a route learned from one iBGP neighbor is normally not advertised to another iBGP neighbor. This behavior prevents routing loops inside an autonomous system. Because of this rule, service-provider networks traditionally require a full iBGP mesh or scalability mechanisms such as Route Reflectors or Confederations. Add-Path allows multiple paths to be advertised but does not remove the basic iBGP advertisement rule by itself. Route Refresh requests updated routes, while MED influences path selection. Therefore, iBGP split horizon is correct.

Question 353

Which BGP mechanism is designed to reduce the requirement for a full iBGP mesh?

1. Route Reflector
2. MED
3. BFD
4. MPLS LDP

Correct Answer: 1

Explanation

A BGP Route Reflector reduces the need for a full iBGP mesh by allowing selected clients to exchange routes through a central route-reflection mechanism. Instead of every iBGP router maintaining a session with every other iBGP router, clients establish sessions with one or more Route Reflectors. This greatly reduces the number of BGP sessions in large networks. MED and BFD serve different purposes, while LDP distributes MPLS labels. Route Reflectors are therefore an important scalability mechanism for large service-provider BGP deployments.

Question 354

Which BGP attribute helps a Route Reflector identify the route’s original advertising client?

1. Originator ID
2. MED
3. Local Preference
4. Weight

Correct Answer: 1

Explanation

The BGP Originator ID is used by Route Reflectors to identify the original router that originated a reflected route. It helps prevent routing loops in route-reflector environments. The Cluster List provides additional loop-prevention information by recording Route Reflector cluster IDs through which the route has passed. MED influences path selection between autonomous systems, Local Preference controls internal path preference, and Weight is locally significant. Therefore, Originator ID is the correct attribute for identifying the original advertising router in a route-reflection environment.

Question 355

Which BGP attribute is used by Route Reflectors to help prevent a reflected route from looping through the same cluster?

1. AS_PATH
2. Cluster List
3. MED
4. NEXT_HOP

Correct Answer: 2

Explanation

The BGP Cluster List helps prevent routing loops in a Route Reflector environment. When a Route Reflector reflects a route, it can add its cluster ID to the Cluster List attribute. If a Route Reflector later receives a route containing its own cluster ID, it can reject the route to prevent a reflection loop. Originator ID identifies the original route originator, while AS_PATH provides autonomous-system loop detection in eBGP scenarios. MED and NEXT_HOP have different functions. Therefore, Cluster List is correct.

Question 356

Which MPLS OAM tool can verify MPLS label-switched path connectivity and help identify failures along the LSP?

1. MPLS LSP Ping
2. BGP Route Refresh
3. SNMP Walk
4. DHCP Discover

Correct Answer: 1

Explanation

MPLS LSP Ping is an OAM mechanism used to verify connectivity through an MPLS Label Switched Path. It can help determine whether an LSP is operational and can provide information about where a forwarding problem may exist. This is particularly useful because ordinary IP ping may not fully validate MPLS label forwarding behavior. BGP Route Refresh is used for route updates, SNMP Walk retrieves management information, and DHCP Discover is part of IP address assignment. Therefore, MPLS LSP Ping is the correct OAM tool.

Question 357

Which MPLS mechanism allows the penultimate router to remove the top label before forwarding traffic to the egress router?

1. Explicit Null
2. Penultimate Hop Popping
3. Label Push
4. PHP Disable

Correct Answer: 2

Explanation

Penultimate Hop Popping (PHP) allows the router immediately before the egress LSR to remove the top MPLS label. This reduces the label-processing work required at the egress router and allows it to perform the necessary IP or VPN lookup with fewer label operations. PHP is commonly associated with an implicit-null label advertisement. Explicit Null is different because it instructs the upstream router to retain an MPLS label, often to preserve QoS-related information. Therefore, Penultimate Hop Popping is correct.

Question 358

Which MPLS label is commonly used to request that the penultimate router retain an MPLS label instead of performing PHP?

1. Implicit Null
2. Explicit Null
3. Label 0 only for IPv4
4. VPN Label

Correct Answer: 2

Explanation

An Explicit Null label can be used to request that the upstream router retain an MPLS label rather than performing normal penultimate hop popping. This can be useful when preserving the MPLS header through the penultimate hop is important, including scenarios involving QoS EXP/Traffic Class handling. An implicit-null label, in contrast, signals that the penultimate router should remove the top label. A VPN label serves a different purpose by identifying a VPN forwarding context. Therefore, Explicit Null is correct.

Question 359

Which service-provider technology is designed to measure packet loss, delay, and delay variation across an Ethernet service?

1. Y.1731
2. RPKI
3. NETCONF
4. LACP

Correct Answer: 1

Explanation

ITU-T Y.1731 defines Ethernet performance monitoring and fault-management capabilities. It can be used to measure service characteristics such as frame loss, delay, and delay variation across Ethernet services. These measurements are valuable for service providers that need to verify service-level objectives and troubleshoot performance problems. RPKI is used for BGP route-origin validation, NETCONF is a network configuration protocol, and LACP manages link aggregation. Therefore, Y.1731 is the correct technology for Ethernet service performance monitoring.

Question 360

Which Ethernet OAM technology uses Maintenance End Points and Maintenance Intermediate Points to monitor Ethernet connectivity domains?

1. BGP
2. CFM
3. RSVP-TE
4. DHCPv6

Correct Answer: 2

Explanation

Connectivity Fault Management (CFM), defined by IEEE 802.1ag, uses Maintenance End Points (MEPs) and Maintenance Intermediate Points (MIPs) to monitor Ethernet connectivity and detect faults within defined maintenance domains. CFM provides mechanisms such as continuity checks and loopback testing that help service providers identify failures in Ethernet-based services. BGP handles routing, RSVP-TE can signal traffic-engineered MPLS tunnels, and DHCPv6 provides IPv6 configuration functions. Therefore, CFM is the correct Ethernet OAM technology.