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Question 241.

In OSPF, what is the primary role of a Type 3 Summary LSA?

1. Advertise inter-area network reachability
2. Describe the local router’s interfaces inside an area
3. Represent a broadcast network generated by the DR
4. Advertise external routes from an ASBR

Correct Answer: 1. Advertise inter-area network reachability

Explanation:

Type 3 Summary LSAs are generated by Area Border Routers to advertise network prefixes from one OSPF area into another. They allow routers to learn inter-area destinations without receiving the full detailed topology of remote areas. This separation is one of the key reasons OSPF scales effectively in multi-area designs. Type 1 LSAs describe router links within an area, Type 2 LSAs represent multi-access networks, and Type 5 LSAs carry external route information.

Question 242.

An OSPF router receives a newer instance of an existing LSA. What should it normally do?

1. Ignore it because an LSA already exists
2. Update its link-state database and flood the newer information as appropriate
3. Convert the LSA into a BGP update
4. Reset every OSPF adjacency

Correct Answer: 2. Update its link-state database and flood the newer information as appropriate

Explanation:

OSPF compares received LSAs with the information already stored in the link-state database. If the received LSA is newer, the router installs the updated information and floods it according to normal OSPF rules. This process helps routers in the same area maintain synchronized topology information. Sequence numbers, age, and other LSA fields help determine which copy is more recent. Updating the LSDB does not require converting information to BGP or resetting all adjacencies.

Question 243.

What is the main purpose of an OSPF virtual link?

1. Increase Ethernet bandwidth
2. Provide MPLS transport
3. Restore logical backbone connectivity when direct Area 0 connectivity is unavailable
4. Replace OSPF authentication

Correct Answer: 3. Restore logical backbone connectivity when direct Area 0 connectivity is unavailable

Explanation:

An OSPF virtual link can logically connect a disconnected area or backbone segment through a transit area when direct Area 0 connectivity is not available. It is generally considered a special or transitional design tool rather than the preferred long-term architecture. OSPF networks are usually easier to operate when backbone connectivity is physically straightforward. Virtual links do not increase bandwidth, provide MPLS forwarding, or replace routing-protocol authentication.

Question 244.

Which OSPF interface setting can prevent a router from participating in DR or BDR election while still allowing it to run OSPF on the segment?

1. Increase the interface cost
2. Configure a passive interface
3. Change the router ID
4. Set the OSPF interface priority to 0**

Correct Answer: 4. Set the OSPF interface priority to 0

Explanation:

An OSPF interface priority of 0 makes the router ineligible to become either the Designated Router or Backup Designated Router on that multi-access segment. The device can still exchange OSPF packets and form the appropriate neighbor relationships. This is useful when administrators want specific routers to handle DR responsibilities. A passive interface would suppress neighbor formation entirely, so it would not meet the requirement of continuing normal OSPF participation on the shared network.

Question 245.

Which BGP attribute is generally used to influence outbound traffic within an autonomous system?

1. Local Preference
2. MED
3. Cluster List
4. Originator ID

Correct Answer: 1. Local Preference

Explanation:

Local Preference is one of the primary BGP attributes used to select preferred outbound paths. Higher Local Preference values are generally favored and are propagated among iBGP peers within the local autonomous system. An organization with multiple upstream providers can therefore assign higher Local Preference to routes learned from the desired primary provider. MED is more commonly used to suggest a preferred inbound entry point to a neighboring AS.

Question 246.

Which BGP attribute is primarily associated with the path of autonomous systems a route has traversed?

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

Correct Answer: 2. AS_Path

Explanation:

The AS_Path attribute contains the sequence of autonomous system numbers through which a BGP route has passed. It is used for loop prevention and also contributes to best-path selection. If a router receives a route containing its own AS number, it normally rejects the route. When earlier path-selection factors are equal, a shorter AS_Path is generally preferred. Communities provide policy tagging, while MED and Local Preference serve different traffic-engineering purposes.

Question 247.

Why is outbound prefix filtering important on an eBGP session?

1. It increases interface bandwidth
2. It replaces route reflectors
3. It helps prevent accidental advertisement of unauthorized prefixes
4. It automatically creates backup paths

Correct Answer: 3. It helps prevent accidental advertisement of unauthorized prefixes

Explanation:

Outbound prefix filtering ensures that only approved network prefixes are advertised to an external BGP neighbor. Without such filtering, redistribution or configuration errors could cause route leaks that affect the local organization or other networks. Prefix lists and routing policies are commonly used to implement these controls. Good BGP boundary design includes both inbound and outbound validation rather than relying only on the protocol’s inherent loop-prevention mechanisms.

Question 248.

What is the main purpose of a BGP route reflector?

1. Replace eBGP between organizations
2. Provide DHCP services
3. Perform MPLS label switching
4. Reduce the requirement for a full mesh of iBGP sessions**

Correct Answer: 4. Reduce the requirement for a full mesh of iBGP sessions

Explanation:

In traditional iBGP, every BGP speaker would need a session with every other speaker to ensure complete route distribution. This becomes difficult to scale as the network grows. A route reflector can advertise selected iBGP routes between clients, dramatically reducing the number of required peerings. Redundant route reflectors are commonly deployed for resilience. Underlying IP reachability is still required, so route reflection does not eliminate the need for an IGP.

Question 249.

In IS-IS, what is the primary function of a Link State PDU?

1. Advertise topology and reachability information
2. Assign IPv6 addresses to hosts
3. Establish BGP peering
4. Elect a VRRP master

Correct Answer: 1. Advertise topology and reachability information

Explanation:

IS-IS routers originate Link State PDUs containing information about their links, neighbors, prefixes, metrics, and other attributes. These LSPs are flooded through the appropriate routing level so routers can build synchronized link-state databases. The routers then run the SPF algorithm to calculate shortest paths. LSPs are therefore fundamental to IS-IS topology distribution and route calculation. They are unrelated to host address assignment or first-hop gateway redundancy.

Question 250.

What does the IS-IS overload bit indicate?

1. The router has the highest priority on the LAN
2. The router should generally not be used as a transit node while the bit is set
3. The router has exceeded its interface bandwidth
4. The router has become the DIS

Correct Answer: 2. The router should generally not be used as a transit node while the bit is set

Explanation:

The overload bit tells other IS-IS routers that the advertising router should generally be avoided for transit traffic. It is useful during startup, maintenance, or temporary conditions where the router is participating in the routing protocol but is not ready to carry normal transit load. Directly connected reachability may remain available. This mechanism can improve stability by reducing the chance that traffic is forwarded through a router whose forwarding or control-plane state has not fully converged.

Question 251.

What is the primary role of LDP in an MPLS network?

1. Distribute label bindings between MPLS-capable routers
2. Configure VRRP priorities
3. Provide Layer 2 loop prevention
4. Replace the routing table

Correct Answer: 1. Distribute label bindings between MPLS-capable routers

Explanation:

Label Distribution Protocol allows MPLS routers to exchange mappings between forwarding equivalence classes and MPLS labels. These label bindings are used to build label forwarding tables and support label-switched paths. An IGP such as OSPF or IS-IS normally supplies the underlying IP reachability, while LDP adds label information. LDP therefore complements routing protocols rather than replacing them. It does not provide first-hop redundancy or Layer 2 loop prevention.

Question 252.

What is the purpose of an outer transport label in a typical MPLS Layer 3 VPN packet?

1. Identify the customer’s application port
2. Transport the packet across the provider network toward the correct egress PE
3. Replace the customer IP address
4. Encrypt the packet payload

Correct Answer: 2. Transport the packet across the provider network toward the correct egress PE

Explanation:

In an MPLS Layer 3 VPN, the outer label commonly represents the transport path through the provider core toward the destination PE router. An inner service or VPN label can then identify the appropriate customer forwarding context at the egress PE. Core P routers can forward based on the outer label without maintaining detailed customer VPN routes. MPLS labels support forwarding and service separation but do not provide payload encryption by themselves.

Question 253.

Which MPLS VPN value is used to make otherwise identical customer prefixes unique in MP-BGP?

1. Route Target
2. VRRP priority
3. Route Distinguisher
4. OSPF area ID

Correct Answer: 3. Route Distinguisher

Explanation:

A Route Distinguisher is combined with an IPv4 prefix to create a unique VPN route in MP-BGP. This is necessary because different customers may use identical private addressing. The Route Distinguisher ensures that those overlapping prefixes can coexist in the provider control plane. It does not determine which VPNs should import the route. Route Targets perform the separate import and export policy function.

Question 254.

Which mechanism determines VPN route membership in an MPLS Layer 3 VPN?

1. Router ID
2. Interface cost
3. VLAN priority
4. Route Target**

Correct Answer: 4. Route Target

Explanation:

Route Targets are extended BGP communities that control which VPN routes are imported and exported by specific VPN instances. This allows an operator to build full-mesh, hub-and-spoke, and shared-services VPN topologies without changing the underlying physical infrastructure. Route Distinguishers provide route uniqueness, whereas Route Targets define route membership and distribution policy. Correct import and export configuration is therefore essential for expected VPN connectivity.

Question 255.

What is the primary purpose of VRRP tracking?

1. Adjust gateway priority when an important interface or route changes state
2. Increase MPLS label depth
3. Select an OSPF DR
4. Create BGP route policies

Correct Answer: 1. Adjust gateway priority when an important interface or route changes state

Explanation:

VRRP tracking allows the effective priority of a participating router to change based on the status of important resources. For example, if the current master loses an upstream WAN interface, its VRRP priority can be reduced so a backup router with healthy connectivity becomes master. This improves first-hop resilience because gateway selection reflects more than just the state of the local LAN interface. Tracking is especially useful when redundant gateways have different upstream paths.

Question 256.

Why might a VRRP preemption delay be configured?

1. To stop the backup router from ever becoming master
2. To give a recovering preferred router time to stabilize before reclaiming mastership
3. To increase OSPF route preference
4. To disable the virtual IP address

Correct Answer: 2. To give a recovering preferred router time to stabilize before reclaiming mastership

Explanation:

A router may recover its local interface before routing protocols, upstream connectivity, or dependent services have fully converged. If it immediately preempts the current VRRP master, traffic could be forwarded through a device that is not yet ready. A preemption delay gives the recovering router time to stabilize before it takes back the master role. This reduces unnecessary disruption during recovery and makes gateway failover behavior more predictable.

Question 257.

What is the primary purpose of LACP within an Eth-Trunk?

1. Negotiate and monitor member links in the aggregation
2. Advertise OSPF routes
3. Provide MPLS VPN separation
4. Assign DHCP addresses

Correct Answer: 1. Negotiate and monitor member links in the aggregation

Explanation:

LACP provides dynamic negotiation and status monitoring for interfaces participating in an Ethernet link aggregation. Devices at both ends exchange information so they can determine which links are suitable to become active members. This helps detect configuration mismatches or failed links and improves the operational reliability of the Eth-Trunk. LACP does not perform Layer 3 routing or MPLS VPN functions.

Question 258.

Which QoS mechanism is designed to enforce a rate by dropping or remarking packets that exceed a configured profile?

1. Traffic shaping
2. Traffic policing
3. BFD
4. Route summarization

Correct Answer: 2. Traffic policing

Explanation:

Traffic policing compares traffic against a defined rate profile and applies an immediate action to packets that exceed the permitted rate. Excess packets may be dropped or remarked according to the policy. This differs from shaping, which normally buffers excess traffic and sends it later. Policing is useful for enforcing bandwidth limits at trust boundaries or service edges. Classification is commonly used first so different traffic classes can receive different policing treatment.

Question 259.

Which technology can accelerate failure detection for OSPF, IS-IS, and BGP without relying only on their normal Hello or keepalive timers?

1. BFD
2. DHCP relay
3. Route Target
4. MSTP

Correct Answer: 1. BFD

Explanation:

Bidirectional Forwarding Detection provides rapid detection of forwarding-path failures and can be associated with several dynamic routing protocols. When BFD declares a path down, the routing protocol can react sooner than it might using normal protocol timers alone. BFD does not calculate routes or choose alternate paths; it simply provides fast liveness information. This makes it valuable in networks where convergence time is an important service requirement.

Question 260.

Which design BEST supports scalability and resilience in a large Huawei routed network?

1. Use uncontrolled redistribution among all routing protocols
2. Disable redundant links
3. Put all services in one large Layer 2 domain
4. Use hierarchical topology, structured addressing, summarization, route filtering, redundancy, fast failure detection, and consistent monitoring**

Correct Answer: 4. Use hierarchical topology, structured addressing, summarization, route filtering, redundancy, fast failure detection, and consistent monitoring

Explanation:

A scalable network depends on clear architectural boundaries and predictable protocol behavior. Hierarchical topology limits failure domains, while structured addressing enables route summarization. Route filtering and policy prevent unintended advertisements, and redundant links and devices improve availability. BFD can accelerate failure detection where required, while monitoring provides operational visibility. OSPF, IS-IS, BGP, MPLS, VRRP, Eth-Trunk, and QoS should be assigned well-defined roles so the overall network remains stable, understandable, and easier to troubleshoot.