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

 

Question 21.

In OSPF, which area must exist as the backbone area and provide inter-area connectivity?

1. Area 0
2. Area 1
3. Area 10
4. Any NSSA

Correct Answer: 1. Area 0

Explanation:

OSPF uses Area 0 as the backbone area. Other standard areas normally connect to the backbone through Area Border Routers so routing information can be exchanged between areas in a structured hierarchy. This design improves scalability by reducing the amount of link-state information every router must maintain. If a non-backbone area cannot connect physically to Area 0, special design mechanisms may sometimes be used, but the fundamental OSPF architecture still treats Area 0 as the backbone. Area numbering other than 0 does not automatically give an area backbone status.

Question 22.

Which OSPF packet type is used to discover neighbors and maintain neighbor relationships?

1. Link State Request
2. Hello packet
3. Link State Update
4. Database Description

Correct Answer: 2. Hello packet

Explanation:

OSPF routers send Hello packets to discover neighboring OSPF devices and verify that existing neighbors remain reachable. Hello packets also carry important parameters that must be compatible for an adjacency to form, such as the area ID and certain timer values. On broadcast networks, Hello packets also participate in DR and BDR election. Other OSPF packet types are used later during database synchronization and LSA exchange. Without successful Hello communication, neighboring routers cannot progress through the normal adjacency states.

Question 23.

What is the main purpose of OSPF cost?

1. Determine the VLAN ID
2. Encrypt routing updates
3. Influence path selection toward a destination
4. Identify the BGP autonomous system

Correct Answer: 3. Influence path selection toward a destination

Explanation:

OSPF uses cost as its routing metric. The total cost of a path is calculated from the costs of the outgoing interfaces along that route, and OSPF generally selects the path with the lowest accumulated cost. Interface cost is commonly associated with bandwidth, although administrators can configure it manually to influence routing decisions. Cost allows network designers to prefer higher-quality or desired paths. It does not identify VLANs, encrypt routing messages, or define BGP autonomous system numbers.

Question 24.

What is the purpose of an OSPF virtual link?

1. Replace BGP route reflectors
2. Provide Layer 2 loop prevention
3. Aggregate Ethernet links
4. Logically connect a disconnected area to the OSPF backbone through another area**

Correct Answer: 4. Logically connect a disconnected area to the OSPF backbone through another area

Explanation:

An OSPF virtual link can provide a logical connection to Area 0 when a non-backbone area does not have a direct physical connection to the backbone. It is configured through a transit area and is generally considered a special design mechanism rather than the preferred long-term architecture. A well-designed OSPF network normally maintains direct backbone connectivity where practical. Virtual links do not provide Ethernet aggregation, spanning-tree functionality, or BGP route reflection.

Question 25.

In BGP, which attribute is normally preferred when it has the smallest value and is used to influence inbound traffic from neighboring autonomous systems?

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

Correct Answer: 1. MED

Explanation:

The Multi-Exit Discriminator, or MED, is a BGP attribute used to suggest which entry point an external neighboring autonomous system should prefer when multiple links exist between the two networks. A lower MED is normally preferred. MED is often useful when one organization advertises the same destination through multiple connections to the same neighboring AS. Local Preference primarily influences outbound path selection inside an autonomous system and typically prefers higher values. Administrators should understand the complete BGP selection process because other attributes may be evaluated before MED.

Question 26.

What is the primary difference between eBGP and iBGP?

1. eBGP works only with IPv6
2. eBGP operates between different autonomous systems, while iBGP operates within the same autonomous system
3. iBGP does not exchange routes
4. eBGP is a Layer 2 protocol

Correct Answer: 2. eBGP operates between different autonomous systems, while iBGP operates within the same autonomous system

Explanation:

External BGP is used to exchange routing information between routers in different autonomous systems, while internal BGP is used to distribute BGP routing information among routers within the same autonomous system. The two forms of BGP share the same basic protocol but have different operational rules and design considerations. Large iBGP deployments often use route reflectors or confederations to reduce full-mesh requirements. Both eBGP and iBGP can carry multiple address families and are Layer 3 routing functions.

Question 27.

Why are route policies commonly used with BGP?

1. To elect the spanning-tree root bridge
2. To create VLAN trunks
3. To control which routes are accepted, advertised, or modified
4. To assign DHCP addresses

Correct Answer: 3. To control which routes are accepted, advertised, or modified

Explanation:

BGP is highly policy driven. Route policies allow administrators to match routes using attributes or prefix information and then permit, deny, or modify those routes. For example, a policy can change Local Preference, MED, communities, or other attributes to influence traffic engineering. Policies can also prevent unwanted prefixes from entering or leaving an autonomous system. This control is essential for both security and predictable routing behavior. VLAN, DHCP, and spanning-tree functions are unrelated to BGP route policy processing.

Question 28.

What is the purpose of BGP communities?

1. Encrypt routing updates
2. Assign interface IP addresses
3. Replace AS numbers
4. Tag routes so routing policies can treat groups of routes consistently**

Correct Answer: 4. Tag routes so routing policies can treat groups of routes consistently

Explanation:

BGP communities provide a flexible way to attach labels or tags to routes. Routers can match these community values in routing policies and apply actions to groups of routes without matching every individual prefix separately. Communities are commonly used for traffic engineering, route filtering, administrative classification, and signaling routing intentions between networks. They do not replace autonomous system numbers or provide encryption. Their main value is simplifying scalable routing policy design and operation.

Question 29.

In IS-IS, which PDU is used to advertise link-state information about the topology?

1. Link State PDU
2. DHCP Discover
3. BGP Update
4. ARP Reply

Correct Answer: 1. Link State PDU

Explanation:

IS-IS routers use Link State PDUs, commonly called LSPs, to advertise topology and routing information throughout an IS-IS level. These LSPs contain information about neighbors, prefixes, metrics, and other attributes represented through TLVs. Routers build a link-state database from the received LSPs and run the SPF algorithm to calculate best paths. The concept is similar to OSPF’s use of LSAs, although the protocol formats and terminology differ. DHCP, BGP, and ARP messages serve unrelated functions.

Question 30.

What is the main purpose of the DIS in an IS-IS broadcast network?

1. Assign IP addresses to routers
2. Simplify adjacency and link-state representation on the multi-access segment
3. Encrypt IS-IS PDUs
4. Replace Level-2 routing

Correct Answer: 2. Simplify adjacency and link-state representation on the multi-access segment

Explanation:

On an IS-IS broadcast network, a Designated Intermediate System is elected to help represent the multi-access segment in the link-state database and coordinate certain protocol functions. This reduces complexity compared with treating every possible router-to-router relationship independently. The DIS concept differs in behavior from the OSPF DR/BDR model, so administrators should not assume the election and failover rules are identical. The DIS does not assign IP addresses or replace Level-2 routing functionality.

Question 31.

What is the primary purpose of an MPLS Label Switched Path?

1. Provide a logical forwarding path through an MPLS network
2. Assign VLAN numbers dynamically
3. Authenticate wireless clients
4. Replace IP addressing on customer devices

Correct Answer: 1. Provide a logical forwarding path through an MPLS network

Explanation:

A Label Switched Path, or LSP, defines the sequence of MPLS forwarding actions used to carry labeled traffic across an MPLS domain. Label-switching routers use labels rather than performing a full IP lookup at every hop for that forwarding context. LSPs can support services such as MPLS VPNs and traffic-engineering designs. The customer traffic still uses normal network-layer addressing where appropriate. MPLS labels and LSPs do not provide wireless authentication or VLAN assignment.

Question 32.

What is the role of a Provider Edge router in an MPLS Layer 3 VPN?

1. It operates only as a Layer 2 access switch
2. It connects customer sites to the provider MPLS network and maintains customer VPN routing information
3. It replaces all customer routers
4. It performs only DNS resolution

Correct Answer: 2. It connects customer sites to the provider MPLS network and maintains customer VPN routing information

Explanation:

A Provider Edge, or PE, router sits at the edge of the service provider network and connects to customer edge devices. In an MPLS Layer 3 VPN, the PE maintains separate customer routing contexts and participates in mechanisms that distribute VPN routes across the provider backbone. This separation allows multiple customers, even those using overlapping address spaces, to share the same provider infrastructure securely at the routing level. Core provider routers generally do not need to maintain all individual customer routes.

Question 33.

In an MPLS Layer 3 VPN, what is the purpose of a VPN instance or VRF?

1. Replace Ethernet switching
2. Create a spanning-tree instance
3. Maintain a separate routing and forwarding table for a customer or VPN
4. Encrypt all MPLS labels

Correct Answer: 3. Maintain a separate routing and forwarding table for a customer or VPN

Explanation:

A VPN routing and forwarding context, commonly referred to as a VRF or VPN instance, keeps routes for one customer or logical VPN separate from routes belonging to other customers. This isolation allows overlapping address spaces to coexist on the same provider edge router without route conflicts. Interfaces and routes are associated with the appropriate VPN context. MPLS VPN designs then use additional identifiers and route-distribution mechanisms to carry this information through the provider network.

Question 34.

What is the primary purpose of a Route Distinguisher in an MPLS Layer 3 VPN?

1. Encrypt VPN routes
2. Determine Ethernet duplex settings
3. Replace route policies
4. Make otherwise identical customer IPv4 prefixes unique in the provider control plane**

Correct Answer: 4. Make otherwise identical customer IPv4 prefixes unique in the provider control plane

Explanation:

Different VPN customers may use the same IPv4 prefixes, such as private address ranges. A Route Distinguisher is combined with the IPv4 prefix to create a unique VPN route in the provider control plane. This prevents overlapping customer prefixes from becoming indistinguishable when they are distributed using MP-BGP. The Route Distinguisher itself does not determine which VPN imports or exports a route; route-target mechanisms are used for that policy function. It also does not provide encryption.

Question 35.

What is the primary purpose of a Route Target in an MPLS Layer 3 VPN?

1. Control the import and export of VPN routes between VPN instances
2. Identify the physical interface speed
3. Elect the OSPF DR
4. Provide label encryption

Correct Answer: 1. Control the import and export of VPN routes between VPN instances

Explanation:

Route Targets are extended BGP communities used to control which VPN routes are imported into or exported from particular VPN routing instances. This allows flexible VPN topologies such as full-mesh, hub-and-spoke, or shared-services designs. Route Distinguishers make overlapping prefixes unique, while Route Targets determine route membership and distribution policy. Administrators should understand this distinction because the two values serve different purposes in MPLS Layer 3 VPN architecture.

Question 36.

Which technology allows multiple customer VPN routes to be carried between provider edge routers using BGP extensions?

1. STP
2. MP-BGP
3. DHCP relay
4. LACP

Correct Answer: 2. MP-BGP

Explanation:

Multiprotocol BGP extends BGP so it can carry multiple address families, including VPN route information used in MPLS Layer 3 VPN environments. Provider edge routers can exchange VPN-specific routes while preserving customer separation through VPN route identifiers and policy attributes. MP-BGP provides the control-plane distribution mechanism, while MPLS labels are used in the forwarding plane. STP, DHCP relay, and LACP perform entirely different functions and do not distribute VPN routing information.

Question 37.

What is the purpose of route redistribution between routing protocols?

1. Allow routes learned by one routing protocol to be introduced into another routing domain
2. Encrypt routing tables
3. Replace route summarization
4. Create Layer 2 trunks

Correct Answer: 1. Allow routes learned by one routing protocol to be introduced into another routing domain

Explanation:

Route redistribution allows routes learned from one source, such as OSPF, IS-IS, BGP, or static configuration, to be advertised into another routing protocol. It is useful during migrations, mergers, or networks that intentionally use multiple routing domains. Redistribution must be designed carefully because incorrect policy can create routing loops, suboptimal paths, or excessive route propagation. Administrators often use filtering, route tagging, and metric control to make redistribution predictable and safe.

Question 38.

What is the main risk of poorly designed bidirectional route redistribution?

1. It automatically disables IP routing
2. Routes may be reintroduced into their original protocol, creating loops or incorrect path selection
3. It prevents VLAN creation
4. It disables Ethernet interfaces

Correct Answer: 2. Routes may be reintroduced into their original protocol, creating loops or incorrect path selection

Explanation:

When two routing protocols redistribute routes into each other, a route can potentially leave its original domain and later be redistributed back into that same protocol. Without careful filtering or tagging, routers may interpret the returned route as a different path, which can create loops, instability, or unexpected routing choices. Route policies and tagging mechanisms are commonly used to identify redistributed routes and prevent them from being reintroduced improperly. Bidirectional redistribution should therefore be implemented only with a clear routing policy.

Question 39.

What is the main purpose of BFD in an IP network?

1. Assign IP addresses
2. Create VPN routing tables
3. Detect forwarding-path failures rapidly
4. Replace all routing protocols

Correct Answer: 3. Detect forwarding-path failures rapidly

Explanation:

Bidirectional Forwarding Detection provides rapid detection of failures between forwarding devices. Routing protocols may have their own Hello or keepalive mechanisms, but their default failure-detection timers may be too slow for applications requiring fast convergence. BFD can operate with routing protocols so a detected forwarding-path failure is communicated quickly, allowing routing to react sooner. BFD does not calculate routes itself; it complements protocols such as OSPF, IS-IS, and BGP by providing faster liveness detection.

Question 40.

Which combination BEST supports a resilient large-scale enterprise or service-provider network?

1. One flat broadcast domain and no dynamic routing
2. Hierarchical routing, redundancy, route policies, fast failure detection, and controlled summarization
3. Static addressing with all redundant paths disabled
4. Unfiltered redistribution between every routing protocol

Correct Answer: 2. Hierarchical routing, redundancy, route policies, fast failure detection, and controlled summarization

Explanation:

Large networks benefit from structured design rather than a single flat topology. Hierarchical routing improves scalability, while summarization reduces routing-table size and limits instability. Redundant links and devices improve availability, and mechanisms such as BFD can accelerate failure detection. Route policies provide control over advertisements and path selection, particularly when BGP or redistribution is involved. Uncontrolled route redistribution and oversized Layer 2 domains increase complexity and can make failures harder to contain. A disciplined layered design provides better scalability, resilience, and operational predictability.