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Question 261.

In OSPF, what is the main purpose of the Link State Database?

1. Store topology information used for SPF path calculation
2. Maintain DHCP address leases
3. Store BGP communities
4. Record Ethernet MAC addresses only

Correct Answer: 1. Store topology information used for SPF path calculation

Explanation:

The OSPF Link State Database contains topology information learned through LSAs within an area. Routers in the same OSPF area attempt to maintain consistent topology databases so they can run the Shortest Path First algorithm and calculate routes independently. The LSDB represents routers, links, networks, metrics, and other OSPF topology details. It is separate from the routing table, which contains the selected routes used for forwarding. DHCP leases, BGP communities, and ordinary Layer 2 MAC forwarding information are maintained by different systems.

Question 262.

Which OSPF packet type requests specific LSAs that a router needs during database synchronization?

1. Hello
2. Link State Request
3. Database Description
4. Link State Acknowledgment

Correct Answer: 2. Link State Request

Explanation:

After OSPF neighbors compare Database Description packets, a router may determine that its local database is missing certain LSAs or contains older versions. It sends Link State Request packets to ask its neighbor for those specific LSAs. The neighbor responds with Link State Update packets containing the requested information. Hello packets discover and maintain neighbors, while acknowledgments confirm successful LSA receipt. Understanding the packet roles is useful when troubleshooting OSPF neighbors that do not progress to the Full state.

Question 263.

What is the main function of an OSPF Link State Acknowledgment packet?

1. Elect the DR
2. Assign a router ID
3. Confirm successful receipt of link-state information
4. Advertise BGP routes

Correct Answer: 3. Confirm successful receipt of link-state information

Explanation:

OSPF relies on reliable flooding of link-state information. Link State Acknowledgment packets confirm that LSAs have been successfully received. This allows the sending router to stop retransmitting acknowledged information and helps maintain consistent link-state databases. Reliable flooding is important because routers calculate paths independently based on their local LSDBs. If topology information is not reliably synchronized, routing inconsistencies can result. Acknowledgment packets do not elect the DR or carry BGP route information.

Question 264.

What is the primary purpose of the OSPF Loading state?

1. Assign interface costs
2. Elect an ABR
3. Create external routes
4. Request and receive missing or newer LSAs before reaching Full state**

Correct Answer: 4. Request and receive missing or newer LSAs before reaching Full state

Explanation:

During the Loading state, OSPF neighbors have already compared database summaries and know which LSAs are missing or outdated. They use Link State Request and Link State Update packets to obtain the required information. Once the necessary databases are synchronized, the adjacency can reach the Full state. A router remaining in Loading may indicate problems with LSA exchange, packet loss, or other adjacency issues. Loading is therefore an important final synchronization stage before a fully established OSPF adjacency.

Question 265.

Which BGP feature allows an administrator to attach policy information to routes without changing the advertised prefix itself?

1. BGP community
2. OSPF cost
3. VRRP priority
4. Ethernet MTU

Correct Answer: 1. BGP community

Explanation:

BGP communities are tags attached to routes so routing policies can classify and process groups of prefixes consistently. A community can indicate that a route should receive a certain Local Preference, be advertised to selected peers, or receive another policy action. This allows scalable routing policy without modifying the underlying destination prefix. Communities are especially useful in large enterprise and service-provider networks where many routes require the same policy treatment. They do not determine interface MTU or first-hop redundancy.

Question 266.

A BGP administrator wants routes learned from one peer to be preferred by routers inside the local AS. Which action is MOST appropriate?

1. Increase their MED
2. Increase their Local Preference
3. Add more AS numbers to their AS_Path
4. Lower VRRP priority

Correct Answer: 2. Increase their Local Preference

Explanation:

Local Preference is propagated among iBGP peers and is designed to influence outbound path selection within an autonomous system. A higher Local Preference generally makes a route more attractive. Therefore, routes learned from a preferred upstream peer can be assigned a higher value than routes learned from secondary peers. Increasing AS_Path length would usually make a route less attractive, while MED is normally used to influence inbound routing decisions in a neighboring AS.

Question 267.

What is the primary purpose of the BGP Originator_ID attribute in a route-reflector environment?

1. Define the MPLS VPN
2. Determine OSPF area membership
3. Help prevent routing loops when routes are reflected
4. Configure Ethernet link aggregation

Correct Answer: 3. Help prevent routing loops when routes are reflected

Explanation:

The Originator_ID attribute is used in BGP route-reflector environments to identify the router that originally advertised a reflected route inside the autonomous system. Route reflectors can examine this information and avoid sending a route back to its originator in a way that could contribute to a loop. Together with the Cluster_List attribute, Originator_ID provides important loop-prevention support for scalable iBGP route reflection. It is unrelated to MPLS VPN identification or OSPF area assignment.

Question 268.

Which BGP attribute records the route-reflector clusters through which a reflected route has passed?

1. MED
2. Local Preference
3. Next_Hop
4. Cluster_List**

Correct Answer: 4. Cluster_List

Explanation:

Cluster_List is used in route-reflector environments to record the reflector clusters through which a BGP route has passed. A route reflector can inspect this list to determine whether the route has already traversed its own cluster and reject the route if necessary. This helps prevent routing loops created by route reflection. Originator_ID provides complementary information about the original iBGP source of the route. These attributes allow iBGP to scale beyond a full mesh without sacrificing loop prevention.

Question 269.

In IS-IS, what is the main purpose of the Complete Sequence Number PDU on a broadcast network?

1. Summarize the LSPs present in the link-state database to assist synchronization
2. Assign an IPv6 prefix
3. Establish a BGP session
4. Configure VRRP mastership

Correct Answer: 1. Summarize the LSPs present in the link-state database to assist synchronization

Explanation:

A Complete Sequence Number PDU, or CSNP, contains summary information about LSPs known in the IS-IS database. On broadcast networks, the DIS periodically sends CSNPs to help other routers verify that their databases are synchronized. A router can compare the CSNP information with its own database and request missing or newer LSPs. This mechanism supports reliable link-state flooding and database consistency. It is unrelated to IP address assignment or first-hop redundancy.

Question 270.

What is the purpose of an IS-IS Partial Sequence Number PDU?

1. Replace the SPF algorithm
2. Request or acknowledge specific LSP information during synchronization
3. Elect the DIS
4. Carry MPLS VPN routes

Correct Answer: 2. Request or acknowledge specific LSP information during synchronization

Explanation:

Partial Sequence Number PDUs, or PSNPs, are used to reference specific LSPs rather than summarize the entire database. Depending on the network type and situation, they can request missing link-state information or acknowledge received LSPs. Together with CSNPs and LSP flooding, PSNPs help IS-IS maintain consistent link-state databases. They do not replace the SPF calculation, which uses the synchronized topology database to calculate routes.

Question 271.

In MPLS, which device is generally responsible for removing the final service label and forwarding traffic into the destination VPN?

1. Egress PE router
2. Customer host
3. Core P router only
4. OSPF DR

Correct Answer: 1. Egress PE router

Explanation:

In an MPLS Layer 3 VPN, the egress PE receives the labeled packet from the provider core and uses the remaining service label to identify the correct customer VPN context or forwarding action. The transport label may already have been removed through penultimate hop popping. After interpreting the service label, the PE forwards the packet toward the appropriate customer edge device. Core P routers generally do not maintain the detailed customer VPN routing information needed for this final service decision.

Question 272.

What is the main benefit of keeping customer VPN routes off core P routers in an MPLS Layer 3 VPN?

1. It eliminates the need for MPLS labels
2. It improves provider-core scalability
3. It prevents PE routers from using BGP
4. It disables customer routing

Correct Answer: 2. It improves provider-core scalability

Explanation:

In a scalable MPLS Layer 3 VPN architecture, core P routers primarily maintain provider infrastructure routes and MPLS forwarding information rather than the full set of customer VPN routes. Customer-specific routing is concentrated on PE routers. This reduces the amount of routing information core devices must process and allows the provider network to grow without requiring every core router to understand every customer prefix. MPLS labels enable customer traffic to cross the core while preserving this separation.

Question 273.

What is the primary purpose of MPLS VPN Route Targets?

1. Make overlapping addresses unique
2. Select the OSPF DR
3. Control VPN route import and export policy
4. Choose the LACP active link

Correct Answer: 3. Control VPN route import and export policy

Explanation:

Route Targets are extended BGP communities used to determine which VPN routes are imported into and exported from VPN instances. They make it possible to create flexible connectivity models such as full-mesh, hub-and-spoke, and shared-service VPNs. Route Distinguishers serve a different purpose by making overlapping prefixes unique in the control plane. The separation between uniqueness and membership policy is a fundamental MPLS Layer 3 VPN concept.

Question 274.

What is the purpose of VRRP advertisement messages?

1. Carry BGP routes
2. Advertise MPLS labels
3. Synchronize OSPF databases
4. Allow VRRP routers to monitor master availability and maintain the virtual gateway role**

Correct Answer: 4. Allow VRRP routers to monitor master availability and maintain the virtual gateway role

Explanation:

The VRRP master sends advertisement messages so backup routers know that it is still operating. If the advertisements stop for the expected interval, a backup can assume that the master is unavailable and begin the election or failover process. This allows hosts to continue using the same virtual default gateway address even when the active physical router changes. VRRP advertisements are therefore central to first-hop gateway redundancy and are independent of dynamic routing updates.

Question 275.

Which condition can cause a VRRP backup to become master?

1. Failure or loss of advertisements from the current master
2. Receipt of an OSPF Type 3 LSA
3. An MPLS label swap
4. Creation of a BGP community

Correct Answer: 1. Failure or loss of advertisements from the current master

Explanation:

Backup routers monitor VRRP advertisements from the master. If the master fails or advertisements are no longer received within the expected timing window, an eligible backup can assume the master role. Tracking mechanisms can also influence effective priority so a router with failed upstream connectivity relinquishes mastership. This allows the virtual gateway to remain available to hosts even when one physical router becomes unavailable.

Question 276.

What is the main purpose of LACP system and port priorities?

1. Select BGP routes
2. Influence which links participate when more aggregation candidates exist than can be active
3. Configure MPLS VPNs
4. Set OSPF area type

Correct Answer: 2. Influence which links participate when more aggregation candidates exist than can be active

Explanation:

LACP uses system and port information to determine how candidate member links participate in an aggregation. When more eligible interfaces exist than can be active simultaneously, priority values can influence which links become active and which remain standby. This provides administrators with more control over link aggregation behavior. These priorities are specific to LACP and should not be confused with VRRP priority, OSPF DR priority, or routing-protocol metrics.

Question 277.

Which QoS action changes a packet’s classification marking so downstream devices can treat it differently?

1. Remarking
2. Route summarization
3. BFD
4. VRRP tracking

Correct Answer: 1. Remarking

Explanation:

Remarking changes a QoS-related packet marking such as DSCP or another supported class indication. Downstream devices can then use the new marking to classify the packet and apply different queuing, policing, shaping, or drop behavior. Remarking is commonly used at trust boundaries where incoming markings should be normalized according to organizational policy. It does not change routing topology or provide failure detection.

Question 278.

What is the primary purpose of QoS queue scheduling?

1. Discover routing neighbors
2. Decide which queued packets are transmitted when bandwidth is congested
3. Assign VPN labels
4. Create Ethernet trunks

Correct Answer: 2. Decide which queued packets are transmitted when bandwidth is congested

Explanation:

When an interface becomes congested, packets may need to wait in queues before transmission. Queue scheduling determines how bandwidth is shared among those queues and which traffic is sent first. Different algorithms can prioritize delay-sensitive traffic, guarantee bandwidth to selected classes, or provide fair service among competing flows. Effective scheduling depends on earlier classification and marking decisions. It manages congestion but does not create additional physical bandwidth.

Question 279.

Why is BFD commonly used with dynamic routing protocols in high-availability networks?

1. It can detect forwarding-path failures rapidly and notify the routing protocol
2. It replaces all routing tables
3. It provides MPLS VPN route separation
4. It configures gateway virtual IP addresses

Correct Answer: 1. It can detect forwarding-path failures rapidly and notify the routing protocol

Explanation:

BFD provides rapid liveness detection between network devices, often much faster than default routing-protocol Hello or keepalive mechanisms. When BFD detects a forwarding-path failure, the associated routing protocol can react and converge to an alternate route. BFD does not calculate routes itself; it supplies failure status to protocols such as OSPF, IS-IS, or BGP. This separation makes it useful when fast convergence is required without aggressively shortening every routing-protocol timer.

Question 280.

Which approach BEST supports reliable operation in a large Huawei network with OSPF, BGP, IS-IS, MPLS, VRRP, LACP, and QoS?

1. Redistribute every route into every protocol without filtering
2. Use a single large Layer 2 failure domain
3. Disable redundant paths to simplify management
4. Use hierarchical architecture, controlled route policy, redundancy, structured addressing, fast failure detection, and consistent operational monitoring**

Correct Answer: 4. Use hierarchical architecture, controlled route policy, redundancy, structured addressing, fast failure detection, and consistent operational monitoring

Explanation:

Large networks remain predictable when protocols and services have clearly defined responsibilities. Hierarchical routing and structured addressing support summarization, while route filtering and policy reduce accidental route propagation. Redundant links, VRRP, LACP, and BFD improve availability and convergence. MPLS provides scalable service transport, and QoS provides controlled treatment during congestion. Monitoring, testing, and change management are equally important because even a technically correct design can become unstable if protocol interactions and failure scenarios are not understood.