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Question 301

Which IS-IS packet is used to establish and maintain an adjacency between neighboring routers?

1. CSNP
2. IIH
3. PSNP
4. LSP

Correct Answer: 2

Explanation

IS-IS Intermediate System-to-Intermediate System Hello (IIH) packets are used to establish and maintain adjacencies between neighboring IS-IS routers. They allow routers to discover each other and exchange information required to form an adjacency. CSNP packets provide a summary of the link-state database, while PSNP packets acknowledge or request specific LSP information. LSPs carry the actual link-state information used to build the IS-IS topology database. Therefore, IIH is the correct packet type for establishing and maintaining IS-IS neighbor relationships.

Question 302

Which IS-IS packet provides a summary of the LSPs known by a router on a broadcast network?

1. IIH
2. PSNP
3. CSNP
4. BGP UPDATE

Correct Answer: 3

Explanation

A Complete Sequence Number PDU (CSNP) provides a summary of the LSPs known by an IS-IS router. On broadcast networks, the Designated Intermediate System can use CSNPs to help synchronize the link-state databases of participating routers. Routers compare the information in CSNPs with their own databases and can request missing or newer LSPs. IIH packets establish and maintain adjacencies, while PSNPs acknowledge or request specific LSPs. BGP UPDATE is unrelated to IS-IS database synchronization. Therefore, CSNP is correct.

Question 303

Which IS-IS packet can be used to request a missing or newer LSP from a neighboring router?

1. PSNP
2. IIH
3. CSNP
4. TCP SYN

Correct Answer: 1

Explanation

Partial Sequence Number PDUs (PSNPs) can be used by IS-IS routers to request missing or newer LSPs from neighboring routers. PSNPs also provide acknowledgment functionality for received LSP information. This helps maintain synchronization of the IS-IS link-state database. CSNPs provide a broader summary of LSP information, particularly on broadcast networks, while IIH packets are used for neighbor discovery and adjacency maintenance. TCP SYN is part of TCP connection establishment and is unrelated to IS-IS. Therefore, PSNP is the correct answer.

Question 304

Which IS-IS mechanism can indicate that a router should not be used as a transit router for normal traffic?

1. Overload bit
2. Route Target
3. MED
4. DSCP

Correct Answer: 1

Explanation

The IS-IS overload bit can indicate that a router should not be used as a transit router for normal traffic. A router may set the overload condition during startup, resource exhaustion, or other circumstances where it does not want to attract transit traffic. Other routers can take this information into account when calculating paths through the IS-IS topology. Route Targets are used with VPN route import and export, MED is a BGP path attribute, and DSCP is used for IP QoS classification. Therefore, the overload bit is correct.

Question 305

Which IS-IS metric type is commonly associated with the traditional narrow metric range?

1. Narrow metric
2. Extended metric
3. BGP metric
4. MPLS metric

Correct Answer: 1

Explanation

Traditional IS-IS implementations use narrow metrics, which have a limited metric range. Modern IS-IS deployments can use extended metrics to support much larger values and more flexible metric handling. Metric values influence shortest-path calculations and therefore affect the paths selected through the IS-IS topology. BGP and MPLS have their own path-selection and forwarding mechanisms and do not define the IS-IS metric format. Therefore, the traditional limited metric format is referred to as the narrow metric.

Question 306

Which OSPF router is elected on a broadcast multiaccess network to represent the segment in the OSPF topology?

1. ASBR
2. ABR
3. DR
4. Route Reflector

Correct Answer: 3

Explanation

The Designated Router (DR) is elected on OSPF broadcast multiaccess networks to reduce the number of OSPF adjacencies and simplify link-state flooding. Instead of every router forming full adjacencies with every other router on the segment, routers establish their primary adjacency relationships through the DR and Backup Designated Router. An ABR connects OSPF areas, while an ASBR connects OSPF to external routing domains. A Route Reflector is a BGP scalability mechanism. Therefore, DR is the correct answer.

Question 307

What is the primary purpose of an OSPF Backup Designated Router?

1. Replace the DR if it fails
2. Redistribute BGP routes
3. Allocate MPLS labels
4. Perform NAT translation

Correct Answer: 1

Explanation

The Backup Designated Router (BDR) provides redundancy for the OSPF Designated Router on a multiaccess network. It maintains the necessary relationships and is prepared to assume the DR role if the current DR fails. This reduces the time and control-plane disruption associated with electing a completely new DR. The BDR does not perform BGP route redistribution, MPLS label allocation, or NAT translation as part of its OSPF role. Therefore, replacing the DR after a failure is the primary purpose of the BDR.

Question 308

Which OSPF LSA type is originated by an ASBR to advertise external routes into an OSPF autonomous system?

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

Correct Answer: 3

Explanation

OSPF Type 5 LSAs are originated by an Autonomous System Boundary Router (ASBR) to advertise external routes into the OSPF domain. These routes may originate from another routing protocol or another autonomous system. Type 1 LSAs describe router information within an area, Type 2 describes broadcast network information from the DR, and Type 3 summarizes inter-area networks through ABRs. Therefore, Type 5 is the correct LSA type for normal external route advertisements.

Question 309

Which OSPF LSA type is used to describe a broadcast or NBMA network segment and is originated by the DR?

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

Correct Answer: 1

Explanation

OSPF Type 2 LSAs, known as Network LSAs, are originated by the Designated Router on broadcast and certain multiaccess network types. They describe the routers connected to the multiaccess segment and help represent that segment in the OSPF link-state topology. Type 3 LSAs are Summary LSAs generated by ABRs, Type 4 LSAs provide reachability information for ASBRs, and Type 7 LSAs are associated with NSSA external routes. Therefore, Type 2 is correct.

Question 310

Which OSPF area type allows an area to contain an ASBR while using Type 7 LSAs for external routes?

1. Stub area
2. Totally stubby area
3. NSSA
4. Backbone area

Correct Answer: 3

Explanation

A Not-So-Stubby Area (NSSA) allows external routes to be introduced into the area while maintaining stub-area characteristics. An ASBR inside an NSSA can originate Type 7 LSAs for external routes. An ABR can translate appropriate Type 7 information into Type 5 LSAs when advertising the routes outside the NSSA. Traditional stub areas restrict external LSAs and therefore are not designed for an internal ASBR to introduce external routes in the same way. Therefore, NSSA is the correct answer.

Question 311

Which OSPF area is responsible for connecting other OSPF areas in the standard hierarchical design?

1. Area 1
2. Area 0
3. NSSA
4. Stub area

Correct Answer: 2

Explanation

OSPF Area 0 is the backbone area and provides the central connectivity between other OSPF areas in the standard hierarchical architecture. Inter-area traffic normally passes through the backbone, and ABRs connect non-backbone areas to Area 0. Designing OSPF around a backbone improves scalability and helps control the scope of link-state information. Area 1 is simply an example of a non-backbone area, while NSSA and stub describe area behaviors rather than replacing the backbone’s architectural role. Therefore, Area 0 is correct.

Question 312

Which OSPF feature can reduce the number of routing entries advertised between areas by combining multiple contiguous prefixes?

1. Summarization
2. Route Refresh
3. Add-Path
4. Label Swapping

Correct Answer: 1

Explanation

OSPF route summarization allows multiple contiguous prefixes to be represented by a broader summary prefix. This can reduce the amount of routing information exchanged between areas and can help limit the impact of topology changes. Summarization is typically configured at appropriate OSPF boundary points, such as ABRs for inter-area routes. Route Refresh and Add-Path are BGP mechanisms, while label swapping belongs to MPLS forwarding. Therefore, summarization is the correct feature for reducing the number of advertised routes through aggregation.

Question 313

Which BGP attribute is considered a transitive path attribute and can carry policy information between autonomous systems?

1. BGP Community
2. Router ID
3. NEXT_HOP only
4. Weight

Correct Answer: 1

Explanation

BGP Communities can carry policy information with routes and, depending on the community type and configuration, can be propagated across autonomous-system boundaries. Communities allow operators to classify routes and apply consistent policies such as modifying local preference, controlling advertisements, or identifying customer traffic. Router ID identifies the BGP speaker, Weight is a Cisco-specific local attribute, and NEXT_HOP identifies the route’s next-hop address. Therefore, BGP Community is the appropriate attribute for carrying policy-related tags between BGP speakers.

Question 314

Which BGP community type provides a larger value space than traditional standard communities?

1. Large Community
2. VLAN Community
3. OSPF Community
4. MPLS Community

Correct Answer: 1

Explanation

BGP Large Communities were introduced to provide a larger and more flexible community format than traditional standard BGP communities. A Large Community consists of three 32-bit values, making it suitable for modern service-provider policy designs where operators need to encode autonomous system, function, region, customer, or other policy information. Standard communities use a smaller two-part representation. Large Communities can be particularly useful for organizations operating complex routing policies across multiple autonomous systems. Therefore, Large Community is the correct answer.

Question 315

Which BGP feature can advertise multiple valid paths to improve path diversity and reduce dependence on a single selected route?

1. Add-Path
2. MED
3. Local Preference
4. Route Dampening

Correct Answer: 1

Explanation

BGP Add-Path allows a BGP speaker to advertise more than one path for the same destination prefix. Normally, BGP advertises only its selected best path to a neighbor, which can hide alternative paths. Add-Path improves path visibility and can support better redundancy, traffic engineering, and convergence in suitable network designs. MED and Local Preference influence path selection, while Route Dampening suppresses unstable routes. Therefore, Add-Path is the correct BGP feature for advertising multiple paths.

Question 316

Which BGP behavior changes the next-hop attribute of routes advertised to an iBGP neighbor so that the advertising router becomes the next hop?

1. AS Override
2. Next-Hop-Self
3. Route Refresh
4. Allowas-in

Correct Answer: 2

Explanation

The BGP Next-Hop-Self function changes the NEXT_HOP attribute of an advertised route so that the advertising router identifies itself as the next hop. This is particularly useful when an iBGP router receives an external route and needs other internal routers to use it as the reachable next hop. Without appropriate next-hop handling, internal routers may not have a route to the original external next-hop address. AS Override modifies AS_PATH information, Route Refresh requests route updates, and allowas-in affects AS loop checking. Therefore, Next-Hop-Self is correct.

Question 317

Which BGP mechanism can provide faster convergence by maintaining multiple paths in the forwarding plane for rapid failure recovery?

1. BGP PIC
2. Route Dampening
3. MED
4. Community

Correct Answer: 1

Explanation

BGP Prefix Independent Convergence (PIC) is designed to improve convergence by allowing backup paths to be prepared in the forwarding infrastructure before a primary path fails. When a failure occurs, traffic can be switched to an already-installed backup path without waiting for the entire BGP process to recalculate and install a new forwarding path. This can significantly reduce convergence time in large service-provider networks. Route Dampening addresses unstable routes, MED influences path selection, and communities carry policy information. Therefore, BGP PIC is correct.

Question 318

Which security mechanism validates whether the origin AS is authorized to advertise a particular IP prefix?

1. RPKI
2. SNMP
3. NTP
4. LACP

Correct Answer: 1

Explanation

Resource Public Key Infrastructure (RPKI) can be used to validate BGP route-origin information. Network operators publish Route Origin Authorizations specifying which autonomous system is authorized to originate a particular prefix and the maximum prefix length allowed. A receiving network can validate BGP announcements against this information and classify them according to the validation result. SNMP is used for network management, NTP synchronizes clocks, and LACP manages aggregated Ethernet links. Therefore, RPKI is the correct technology for validating route origin authorization.

Question 319

Which mechanism can limit the number of routes accepted from a BGP neighbor to protect router resources?

1. Maximum-prefix
2. Route Target
3. OSPF Cost
4. MPLS BoS

Correct Answer: 1

Explanation

The BGP maximum-prefix feature allows an administrator to specify how many prefixes a router should accept from a particular neighbor. This provides an important protection mechanism against accidental route leaks, configuration mistakes, or unexpectedly large routing tables. When the configured threshold is exceeded, the router can take a configured action depending on platform and policy. Route Targets control MPLS VPN route import and export, OSPF cost influences IGP path selection, and MPLS BoS identifies the bottom of a label stack. Therefore, maximum-prefix is correct.

Question 320

Which BGP feature allows a router to request updated route advertisements after an inbound policy has been changed without resetting the BGP session?

1. Graceful Restart
2. Route Refresh
3. AS Override
4. BGP Confederation

Correct Answer: 2

Explanation

BGP Route Refresh allows a router to request that a neighbor resend its routing information without tearing down the existing BGP session. This is particularly useful when inbound route policies are modified because the router can obtain fresh advertisements and apply the updated policy without performing a disruptive session reset. Graceful Restart addresses temporary control-plane restart conditions, AS Override modifies AS_PATH information in specific VPN designs, and BGP Confederations provide an architectural scalability mechanism. Therefore, Route Refresh is the correct feature for refreshing routes after an inbound policy change.