View Full Huawei H12-831 Exam Dumps and Practice Test Dumps

 

Question 201.

In OSPF, which router maintains separate link-state databases for each area to which it belongs?

1. Area Border Router
2. Designated Router
3. Backup Designated Router
4. Internal router only

Correct Answer: 1. Area Border Router

Explanation:

An Area Border Router participates in more than one OSPF area and therefore maintains a separate link-state database for each connected area. It exchanges inter-area routing information and can summarize routes between areas where the design permits. This separation helps OSPF scale because detailed topology information does not need to be flooded unchanged throughout the entire routing domain. A Designated Router serves a different purpose on multi-access networks, while an internal router normally has all OSPF interfaces in the same area.

Question 202.

Which OSPF feature is most useful when a remote branch area should receive minimal external routing detail?

1. Route reflection
2. Stub-area design
3. MPLS penultimate hop popping
4. BGP communities

Correct Answer: 2. Stub-area design

Explanation:

A stub-area design limits certain external routing information from entering the area and commonly allows routers to rely on a default route toward the ABR for destinations outside the OSPF domain. This reduces the amount of link-state and routing information that branch routers must maintain. Stub areas are useful when the remote site has a simple topology and does not need detailed knowledge of external routes. The exact area type must match the site’s redistribution requirements because ordinary stub areas have restrictions on external route introduction.

Question 203.

What is the main purpose of the OSPF sequence number carried in LSAs?

1. Assign interface bandwidth
2. Select the DR
3. Help routers distinguish newer link-state information from older information
4. Create a BGP route policy

Correct Answer: 3. Help routers distinguish newer link-state information from older information

Explanation:

OSPF uses LSA sequence numbers to identify newer instances of link-state information. When routers receive multiple versions of an LSA, the sequence information helps them determine which version is more recent and should be retained in the link-state database. This is essential for maintaining consistent topology information throughout an area. LSA aging and sequence numbers work together to prevent stale topology information from remaining indefinitely. The sequence number is unrelated to interface bandwidth or BGP policy.

Question 204.

Why does OSPF use a Backup Designated Router on broadcast networks?

1. To assign DHCP addresses
2. To provide a second default gateway for hosts
3. To replace the ABR
4. To provide a standby for the DR role if the DR fails**

Correct Answer: 4. To provide a standby for the DR role if the DR fails

Explanation:

On broadcast multi-access networks, OSPF elects both a DR and a BDR. The BDR monitors the shared segment and is prepared to take over the DR role if the existing DR becomes unavailable. This reduces the disruption that would otherwise occur if the network had to begin the role-selection process from scratch after every DR failure. The DR and BDR functions relate to OSPF adjacency and LSA exchange on shared media, not host gateway redundancy or DHCP service.

Question 205.

Which BGP attribute is normally used to prevent inter-AS routing loops?

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

Correct Answer: 1. AS_Path

Explanation:

The AS_Path attribute records the autonomous systems through which a BGP route has passed. When a BGP router receives a route containing its own AS number in the path, it normally rejects that route. This provides a fundamental inter-AS loop-prevention mechanism. AS_Path length is also used in BGP best-path selection. Local Preference, MED, and communities are useful for policy and traffic engineering, but they do not provide the same direct loop-prevention function.

Question 206.

An enterprise has two internet links and wants internal routers to prefer Provider A for outbound traffic. Which configuration is MOST appropriate?

1. Increase MED on Provider A routes
2. Assign a higher Local Preference to routes learned from Provider A
3. Prepend the local AS to Provider A advertisements
4. Reduce VRRP priority on Provider A

Correct Answer: 2. Assign a higher Local Preference to routes learned from Provider A

Explanation:

Local Preference is specifically suited to selecting preferred outbound exits within an autonomous system. Routes learned from Provider A can be assigned a higher Local Preference so iBGP routers generally favor that provider over alternatives. MED is more commonly used to influence how an external neighboring AS enters the local network. AS_Path prepending is often used to make an advertised path less attractive to external networks. VRRP priority controls first-hop gateway mastership and is unrelated to BGP path preference.

Question 207.

What is the purpose of BGP AS_Path prepending?

1. Make a route appear shorter
2. Encrypt the BGP advertisement
3. Make a selected advertised path appear less attractive to external peers
4. Create a new autonomous system

Correct Answer: 3. Make a selected advertised path appear less attractive to external peers

Explanation:

AS_Path prepending adds repeated copies of the local AS number to a route advertisement. Because BGP commonly prefers shorter AS paths when earlier decision factors are equal, the prepended route may become less attractive to external networks. This is frequently used to influence inbound traffic across multiple external links. However, remote networks may apply routing policies that override AS_Path length, so prepending influences path selection but does not guarantee the result.

Question 208.

What is the role of a route reflector client in an iBGP design?

1. It must peer with every BGP router in the AS
2. It becomes an eBGP router automatically
3. It replaces the IGP
4. It can receive and advertise iBGP routes through a route reflector without maintaining a full iBGP mesh**

Correct Answer: 4. It can receive and advertise iBGP routes through a route reflector without maintaining a full iBGP mesh

Explanation:

Route reflector clients establish iBGP sessions with one or more route reflectors rather than requiring sessions with every iBGP speaker in the autonomous system. The route reflector can advertise selected routes between clients and other peers, reducing the number of sessions required in large networks. This improves control-plane scalability. Redundant reflectors are commonly used to avoid a single point of failure. The IGP is still required to provide underlying reachability between BGP devices.

Question 209.

In IS-IS, what is the main purpose of LSP flooding?

1. Distribute topology information so routers can build a consistent link-state database
2. Assign DHCP addresses
3. Create VRRP groups
4. Replace SPF calculation

Correct Answer: 1. Distribute topology information so routers can build a consistent link-state database

Explanation:

IS-IS routers originate Link State PDUs that describe their topology and reachability information. These LSPs are flooded throughout the appropriate routing level so routers can build consistent link-state databases. Each router then runs SPF to calculate the best paths based on that topology. Reliable flooding is therefore fundamental to correct IS-IS operation. It does not replace SPF; instead, flooding provides the information that SPF uses for route calculation.

Question 210.

Which IS-IS mechanism can help prevent a newly restarted router from immediately carrying transit traffic before its control plane is fully stable?

1. Route Target filtering
2. Overload bit
3. VRRP preemption
4. Ethernet flow control

Correct Answer: 2. Overload bit

Explanation:

The IS-IS overload bit can advertise that a router should generally not be used as a transit node while the condition is active. A restarted router can participate in the routing protocol and advertise its directly connected reachability while other routers avoid using it for transit paths. Once the router’s control and forwarding planes are stable, the overload bit can be cleared. This helps reduce temporary blackholing during startup or maintenance and improves overall routing stability.

Question 211.

What is the main purpose of MPLS LDP?

1. Create Layer 2 loops
2. Assign public addresses to hosts
3. Exchange label bindings used for MPLS forwarding
4. Elect BGP route reflectors

Correct Answer: 3. Exchange label bindings used for MPLS forwarding

Explanation:

Label Distribution Protocol allows MPLS routers to exchange mappings between forwarding equivalence classes and labels. These bindings help routers create label forwarding entries and establish label-switched paths through the MPLS network. The underlying IGP typically supplies IP reachability, while LDP distributes labels corresponding to that reachability. LDP therefore works alongside OSPF or IS-IS rather than replacing them. It is unrelated to public address assignment or route-reflector election.

Question 212.

What does an MPLS egress router commonly do when a labeled packet reaches the end of its label-switched path?

1. Add unlimited new labels
2. Convert the packet into a Layer 2 broadcast
3. Increase the BGP AS_Path
4. Remove or process the remaining MPLS label and forward the packet appropriately**

Correct Answer: 4. Remove or process the remaining MPLS label and forward the packet appropriately

Explanation:

At the end of an MPLS label-switched path, the egress router processes the remaining label information and forwards the packet according to the service or destination context. In some cases, the outer transport label has already been removed by the penultimate router. For an MPLS VPN, the egress PE may still use an inner service label to identify the proper VRF. MPLS label handling therefore changes as the packet moves from ingress through transit to egress.

Question 213.

Which MPLS Layer 3 VPN component directly connects to a customer edge router?

1. Provider Edge router
2. Provider core P router only
3. Route reflector only
4. LDP-only router

Correct Answer: 1. Provider Edge router

Explanation:

A Provider Edge router connects directly to customer edge devices and maintains the VPN routing context required for those customer sites. It can exchange customer routes using static routing, OSPF, BGP, or another supported PE-CE routing mechanism. The PE then uses MP-BGP and MPLS mechanisms to transport VPN routing information and traffic across the provider network. Core P routers generally forward labeled traffic without directly connecting to customer sites or maintaining customer VRFs.

Question 214.

What is the role of Route Targets in a shared-services MPLS VPN design?

1. Increase MPLS label size
2. Control which VPNs import and export routes to the shared service
3. Assign customer IP addresses
4. Determine OSPF DR priority

Correct Answer: 2. Control which VPNs import and export routes to the shared service

Explanation:

Route Targets provide flexible VPN route membership policy. In a shared-services design, customer VRFs can import routes for common services while the shared-services VRF imports only the customer routes required for return connectivity. By carefully selecting import and export Route Targets, administrators can control which VPNs communicate with the shared service without necessarily allowing direct communication between all customers. This is one of the key advantages of policy-driven MPLS Layer 3 VPN architecture.

Question 215.

What is the primary purpose of VRRP preemption?

1. Allow a higher-priority router to reclaim the master role after recovery
2. Prevent any router from becoming master
3. Disable gateway redundancy
4. Increase OSPF route cost

Correct Answer: 1. Allow a higher-priority router to reclaim the master role after recovery

Explanation:

When preemption is enabled, a VRRP router with a higher effective priority can take over the master role from a lower-priority router after it becomes available again. This is useful when one router is intentionally preferred for normal gateway forwarding. A preemption delay may be configured so the recovering router has time to restore upstream routing and other dependent services before taking over. Preemption affects first-hop gateway selection rather than dynamic routing metrics.

Question 216.

Why might VRRP preemption be delayed after a router restarts?

1. To permanently disable the router
2. To allow routing and upstream connectivity to stabilize before it becomes master
3. To increase the virtual IP address
4. To create an MPLS VPN

Correct Answer: 2. To allow routing and upstream connectivity to stabilize before it becomes master

Explanation:

A router can become operational on its LAN before all upstream routes and services are fully restored. If it immediately preempts the current VRRP master, hosts may start using a gateway that is not yet ready for complete forwarding. A preemption delay gives routing protocols and other dependencies time to converge. Once the router is stable, it can safely reclaim the master role. This improves first-hop redundancy behavior during device recovery.

Question 217.

What is the main purpose of the hash algorithm used by an Eth-Trunk?

1. Select which active member link carries a particular traffic flow
2. Encrypt Ethernet frames
3. Create OSPF LSAs
4. Assign BGP communities

Correct Answer: 1. Select which active member link carries a particular traffic flow

Explanation:

An Eth-Trunk typically uses a hash based on selected packet fields to determine which active member link should carry a traffic flow. This distributes multiple flows across the available links while helping maintain packet ordering within individual flows. The exact fields used can depend on configuration and platform capabilities. Because a single flow may hash to one member, one large flow does not necessarily use the combined bandwidth of every link, even though aggregate capacity increases across many flows.

Question 218.

Which QoS mechanism is most appropriate for enforcing a strict traffic-rate limit without buffering excess packets for later transmission?

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

Correct Answer: 2. Traffic policing

Explanation:

Traffic policing measures traffic against a defined rate and generally takes immediate action on packets that exceed the allowed profile. Excess packets can be dropped or remarked depending on policy. This differs from shaping, which buffers excess traffic and transmits it later to smooth bursts. Policing is useful for enforcing contractual or administrative bandwidth limits where buffering is not desired. It is often combined with classification and marking so different traffic types can receive different rate limits.

Question 219.

A routed network requires very fast failure detection without significantly shortening every routing-protocol timer. Which technology is MOST suitable?

1. BFD
2. DHCP snooping
3. MSTP
4. Route Target filtering

Correct Answer: 1. BFD

Explanation:

Bidirectional Forwarding Detection provides rapid liveness detection independently of the normal Hello or keepalive mechanisms used by routing protocols. OSPF, IS-IS, or BGP can react to a BFD failure notification and converge more quickly without requiring aggressively short native timers throughout the network. BFD does not calculate routes itself; it provides fast path-status information to the routing protocol. This makes it especially useful in networks with strict convergence objectives.

Question 220.

Which design BEST supports stable operation in a large Huawei network using OSPF, IS-IS, BGP, MPLS, VRRP, Eth-Trunk, and QoS?

1. Use unrestricted redistribution between all protocols
2. Disable route filtering to simplify configuration
3. Build one flat broadcast domain
4. Use hierarchical design, clear protocol roles, route policy, summarization, redundancy, fast failure detection, and consistent operational monitoring**

Correct Answer: 4. Use hierarchical design, clear protocol roles, route policy, summarization, redundancy, fast failure detection, and consistent operational monitoring

Explanation:

Large networks remain manageable when routing, transport, redundancy, and QoS technologies are given clearly defined roles. Hierarchical design and structured addressing support summarization, while route policies control advertisement and redistribution. Redundant paths, VRRP, Eth-Trunk, and BFD improve availability and convergence. MPLS can provide scalable service separation, and QoS can deliver predictable treatment during congestion. Continuous monitoring and tested failover behavior help operators identify problems early and reduce the risk of complex protocol interactions causing widespread outages.