Huawei H12-821 Exam Dumps & Practice Test Questions

Question 1:

In OSPF, to avoid routing loops between areas, routing information cannot be exchanged directly between two non-backbone areas. Instead, it can only be shared within an area or between the backbone (Area 0) and a non-backbone area. 

Because of this, every Area Border Router (ABR) must have a connection to the backbone area. Is this statement true or false?

A. TRUE
B. FALSE

Answer: A

Explanation:

Open Shortest Path First (OSPF) is a widely used interior gateway protocol that uses a link-state routing method. One of its key design principles is to divide large networks into smaller, more manageable segments called areas. This segmentation helps reduce routing overhead and improves scalability by limiting how much routing information each router must handle.

A critical aspect of OSPF’s design is the backbone area, designated as Area 0. The backbone serves as the central hub through which all inter-area routing information must pass. This design prevents routing loops and ensures consistent routing paths across the network.

The rule that OSPF does not allow direct routing information exchange between two non-backbone areas (also called stub or standard areas) is essential for loop prevention. Instead, routing updates from one non-backbone area must pass through the backbone area before reaching another non-backbone area.

This routing constraint means that every Area Border Router (ABR), which connects multiple areas, must have at least one interface in the backbone area. Without a direct connection to Area 0, an ABR cannot properly route packets between areas, leading to routing issues and possible network segmentation.

In summary, this architecture ensures that all inter-area routing updates funnel through the backbone area, maintaining a loop-free topology. Therefore, the statement that each ABR must connect to Area 0 to prevent inter-area loops is accurate, making the correct answer TRUE.

Question 2:

Which of the following statements about OSPF packet types is incorrect?

A. Database Description (DD) packets include all Link-State Advertisement (LSA) information and can be used to synchronize the entire Link-State Database (LSDB) periodically between neighbors.
B. Hello packets are utilized to discover neighbors, maintain OSPF relationships, and elect the Designated Router (DR) and Backup Designated Router (BDR) on broadcast and NBMA networks.
C. For two routers to establish an OSPF neighbor relationship, they must send Hello packets at the same interval.
D. DD packets contain only LSA headers that summarize link-state information.

Answer: A

Explanation:

Understanding the role of different OSPF packet types is fundamental to grasping how OSPF neighbors establish and maintain their routing tables.

Option A incorrectly states that Database Description (DD) packets carry all LSA information and are used to periodically synchronize the entire Link-State Database (LSDB) between neighbors. This is false. DD packets actually contain only LSA headers, which are summaries of link-state information, not the full LSA contents. These headers help routers compare their databases to identify missing or outdated LSAs. Once differences are identified, routers request the full LSAs through Link-State Request (LSR) packets, and the updates are delivered via Link-State Update (LSU) packets. Thus, DD packets initiate synchronization but don’t carry the full detailed LSAs.

Option B accurately describes the function of Hello packets. Hello packets are essential for discovering and maintaining neighbor relationships and are also involved in the election of the Designated Router (DR) and Backup Designated Router (BDR) on broadcast and NBMA networks, where router coordination is necessary.

Option C is correct as well. For two routers to form an OSPF neighbor relationship, they must agree on parameters like the Hello interval. If the Hello intervals don’t match, neighbors will not form because these intervals govern how routers detect each other’s presence and failure.

Option D is true because DD packets only carry LSA headers that summarize the state of links in the network, facilitating efficient database comparison.

In conclusion, option A is false due to its incorrect assertion about DD packet contents, making it the correct answer.

Question 3:

Which statement accurately describes the relationship between OSPF neighbors and adjacencies?

A. Not every neighbor establishes an adjacency.
B. Neighbor relationships are chosen from existing adjacencies to share routing info.
C. OSPF routers must form an adjacency before exchanging any routing information.
D. OSPF adjacencies are maintained using Database Description (DD) packets.

Answer: A

Explanation:

In OSPF (Open Shortest Path First), understanding the difference between neighbors and adjacencies is crucial to grasp how routers communicate and share routing information. A neighbor is any router that shares a common network segment, but not all neighbors form a full adjacency, which is a more advanced, synchronized relationship required for exchanging complete routing information.

Option A is correct because not all neighbors form adjacencies. On broadcast and non-broadcast multi-access networks, routers typically form full adjacencies only with the Designated Router (DR) and Backup Designated Router (BDR), while other neighbors remain in a lesser state. On point-to-point links, routers generally form adjacencies with their single neighbor. This selective adjacency formation helps reduce overhead and improves efficiency.

Option B incorrectly suggests that neighbor relationships are selected from adjacencies, but it’s actually the other way around: neighbors are identified first, and then some neighbors develop adjacencies.

Option C is misleading because although routers exchange some basic information when becoming neighbors, full synchronization of routing databases (the complete exchange of link-state data) only happens after establishing an adjacency. Routers do not need a full adjacency to exchange some initial data, but for complete routing info synchronization, adjacency is necessary.

Option D is incorrect because Database Description (DD) packets are only used during the initial adjacency formation to describe link-state databases. They are not used to maintain adjacencies over time; instead, periodic hello packets and Link State Advertisements (LSAs) maintain the relationship.

In summary, not all neighbors become adjacencies in OSPF, depending on network type and roles, making A the correct and most accurate statement.

Question 4:

Which of the following statements about OSPF LSA packet types is incorrect?

A. LS Update packets carry complete LSA information.
B. LS Acknowledgment packets carry complete LSA information.
C. LS Request packets include only LS Type, LS ID, and Advertising Router fields.
D. Database Description packets contain LSA summary info, including LS Type, LS ID, Advertising Router, and Sequence Number.

Answer: B

Explanation:

OSPF uses different packet types to manage and exchange Link State Advertisements (LSAs), which are the fundamental data units routers use to share routing information. It’s important to understand the contents and roles of each packet type to grasp how OSPF synchronizes routing data.

Option A is true because LS Update packets contain the full details of LSAs. These packets are responsible for delivering the actual link-state information that routers need to update their routing tables and maintain an accurate view of the network topology.

Option B is false and thus the correct answer to this question. LS Acknowledgment (LS Ack) packets do not carry full LSA data. Their sole purpose is to acknowledge the receipt of LS Update packets, ensuring reliable delivery. They do not contain routing information but rather act as confirmations.

Option C is accurate. LS Request packets are sent by routers that need specific LSAs they don’t yet have. These requests include only the minimal identifying information: LS Type, LS ID, and Advertising Router, which tells the neighboring router exactly which LSA to send.

Option D is also true. Database Description (DD) packets are exchanged during adjacency formation and contain summary information about LSAs, such as LS Type, LS ID, Advertising Router, and Sequence Number. They allow routers to compare databases quickly without transferring full LSA contents initially.

To summarize, LS Update packets carry complete LSA information, LS Ack packets merely acknowledge receipt without including LSA data, LS Request packets specify which LSA is needed using minimal info, and DD packets provide LSA summaries. Therefore, the incorrect statement is B.

Question 5:

Which cost metrics are recognized and used by the IS-IS routing protocol? (Select all that apply.)

A. default
B. wide
C. ToS
D. narrow

Answer: A, B, D

Explanation:

IS-IS (Intermediate System to Intermediate System) is a link-state routing protocol that calculates the best path to a destination by using cost metrics assigned to network links. The protocol supports several cost types that influence how routes are selected and optimized.

Default cost is the standard metric used by IS-IS and represents the basic link cost value when no other metric type is specified. It’s the most common cost type in practice and is typically a numeric value reflecting link bandwidth or other criteria.

The wide metric was introduced to accommodate larger metric ranges than the default, allowing IS-IS to support more granular path selection in complex or high-capacity networks. This is important in modern environments where links may have very high bandwidths, requiring more flexible metric scales.

The narrow metric is the original metric system used by older versions of IS-IS. It has a smaller range (1-63) and was suitable for simpler or legacy networks. Though less common now, narrow metrics are still supported for backward compatibility with older systems.

The option ToS (Type of Service) is not directly a cost type in IS-IS. While ToS fields relate to Quality of Service (QoS) and can influence routing decisions in other protocols, IS-IS does not use ToS as a cost metric. ToS is more relevant to IP-layer routing rather than link-state protocol metrics.

In summary, IS-IS supports default, wide, and narrow metrics to calculate the best route, each serving different network requirements and scales. The ToS cost type is not applicable in IS-IS routing decisions, so it is excluded.

Question 6:

Which of the following statements about IS-IS Hello (IIH) packets are accurate? (Select all that apply.)

A. Level-1 LAN IIH packets do not include the System ID field.
B. Point-to-Point IIH packets and LAN IIH packets are identical in structure.
C. Point-to-Point IIH packets do not contain a Priority field.
D. Level-1 LAN IIH packets are transmitted using multicast.

Answer: C, D

Explanation:

IS-IS is a link-state protocol that uses Hello packets, known as Intermediate System Hello (IIH) packets, to establish and maintain neighbor relationships. These IIH packets differ slightly depending on the type of link—whether it's a point-to-point (P2P) link or a LAN.

Firstly, the System ID field is a critical identifier in IS-IS Hello packets. It uniquely identifies each router within the routing domain and is included in both Level-1 and Level-2 IIH packets, whether on LAN or point-to-point links. Therefore, the claim that Level-1 LAN IIH packets lack the System ID field is false.

Secondly, P2P IIH packets and LAN IIH packets differ structurally. P2P packets have a simpler design since they involve direct communication between two routers, while LAN IIH packets include additional fields like the Priority field to manage multi-access networks. This Priority field helps elect a Designated Router (DR) in LAN environments where multiple routers share the same medium.

Thirdly, the Priority field is not present in P2P IIH packets. Since there are only two routers on a point-to-point link, there's no need for priority-based election, unlike on LANs where multiple routers might compete for the DR role.

Finally, Level-1 LAN IIH packets are sent using multicast. This allows all routers on the LAN segment to receive these Hello packets, facilitating neighbor discovery and adjacency formation. In contrast, P2P IIH packets are unicast between the two connected routers.

To summarize, statements C and D are correct: P2P IIH packets omit the Priority field, and Level-1 LAN IIH packets are sent via multicast. Statements A and B are incorrect due to misunderstandings about the System ID field and differences between P2P and LAN IIH packets.

Question 7:

Can two Level-1 OSPF routers in different areas form a neighbor adjacency?

A. TRUE
B. FALSE

Answer: B

Explanation:

In the OSPF routing protocol, routers are classified based on their roles and the areas they serve. Level-1 routers operate strictly within a single OSPF area and manage intra-area routing. For two OSPF routers to form a neighbor relationship, they must be in the same area because OSPF adjacency establishment depends on sharing the same area identifier.

Level-1 routers are designed to exchange routing information only inside their specific area. They do not communicate directly with routers outside their area. Instead, when communication across different areas is necessary, it is handled by Level-2 routers, which facilitate inter-area routing.

If two routers are located in separate areas, they cannot form a Level-1 adjacency. Instead, Area Border Routers (ABRs) act as intermediaries, connecting these areas. The ABRs maintain Level-1 adjacency with routers inside their areas and Level-2 adjacency with other ABRs or routers in different areas, effectively managing routing information exchange between areas.

This hierarchical design optimizes OSPF’s scalability and efficiency by limiting routing update propagation within areas and reducing routing table sizes.

Therefore, the statement that two Level-1 routers in different areas can establish a neighbor relationship is false. They are restricted to intra-area communication, and inter-area communication requires a Level-2 router or ABR. Option B is correct because Level-1 routers cannot form neighbor relationships across distinct areas in OSPF.

Question 8:

Which attribute is mandatory and must always be included in a BGP Update message?

A. local-Pref
B. MED
C. AS_Path
D. PrefVal

Answer: C

Explanation:

In BGP (Border Gateway Protocol), Update messages are fundamental for sharing routing information between routers. These messages contain several attributes that influence route selection and ensure loop-free routing. However, not all attributes are mandatory in every Update message.

The AS_Path attribute is critical and must always be included in BGP Update messages. It contains a list of Autonomous Systems (ASes) that the routing information has passed through. This list allows routers to detect routing loops by checking if their own AS number appears in the path, thus preventing routing loops which can cause network instability.

On the other hand, attributes like local-Pref (local preference) and MED (Multi-Exit Discriminator) are optional and serve specific purposes. Local preference is used internally within an AS to influence outbound routing decisions but is not required in all Update messages. MED is also optional and influences inbound traffic routing when multiple exit points from an AS exist.

PrefVal is not a recognized standard BGP attribute. It appears to be a hypothetical or misnamed attribute and is not part of the BGP specification.

Thus, the only attribute that is mandatory and consistently carried in every BGP Update message is the AS_Path. It is essential for routing decisions and loop prevention, making option C the correct answer.

Question 9:

What is the primary role of the Designated Router (DR) in an OSPF broadcast network environment?

A. Routes packets to external networks
B. Minimizes the number of OSPF adjacencies required among routers
C. Handles NAT translation for devices inside the network
D. Assigns IP addresses to devices on the network

Correct Answer: B

Explanation:

In OSPF (Open Shortest Path First), especially in broadcast or multi-access networks like Ethernet LANs, the concept of a Designated Router (DR) plays a crucial role in optimizing network efficiency. Without a DR, each OSPF router on a broadcast network would have to establish a full adjacency with every other router. This results in a large number of adjacencies growing exponentially with the number of routers (n routers require n(n-1)/2 adjacencies). For example, in a network with five routers, ten separate adjacencies would be needed, creating significant overhead in terms of CPU processing and bandwidth usage.

To reduce this complexity, OSPF elects a Designated Router (DR) and a Backup Designated Router (BDR). The DR acts as a central point for exchanging routing information, meaning that other routers on the segment form adjacencies only with the DR and BDR instead of with every other router. This design dramatically reduces the number of adjacencies to about 2n-2, which is far more scalable.

The DR also handles the responsibility of generating Link State Advertisements (LSAs) for the network segment, ensuring that routing information is efficiently disseminated to all OSPF routers. It effectively simplifies the flooding of LSAs by acting as a relay point, improving synchronization of the routing tables. The BDR remains on standby to take over if the DR fails, thus maintaining network stability.

This DR/BDR election process is determined first by the OSPF router priority, and in the case of ties, the router with the highest router ID is elected. Understanding this mechanism is essential for those preparing for Huawei’s HCIP-Datacom-Core certification (H12-821) as it underpins how OSPF functions in real-world large-scale enterprise networks. Mastery of these details not only aids in passing the exam but also provides a solid foundation for designing and troubleshooting complex OSPF networks.

Question 10:

In OSPF, what is the role of the Backup Designated Router (BDR) on a broadcast network segment?

A. It serves as a secondary router that takes over the DR responsibilities if the DR fails
B. It balances the routing load between multiple routers on the segment
C. It assigns IP addresses to devices on the broadcast network
D. It initiates external routing updates to non-OSPF networks

Correct Answer: A

Explanation:

Understanding the roles of the Designated Router (DR) and Backup Designated Router (BDR) is vital for mastering OSPF behavior in broadcast networks, a key topic in Huawei’s H12-821 HCIP-Datacom-Core certification. In broadcast environments, such as Ethernet LANs, multiple routers may exist on the same network segment, and they need to exchange routing information efficiently.

The Designated Router (DR) is elected to serve as the central communication point for all OSPF routers on that segment, minimizing the number of adjacencies and simplifying LSA (Link State Advertisement) flooding. However, to maintain network stability and avoid disruption, a Backup Designated Router (BDR) is also elected.

The primary role of the BDR is to act as a standby or secondary DR. It continuously synchronizes its link-state database with the DR, staying updated on all network topology changes. If the DR becomes unavailable due to a failure or maintenance, the BDR automatically assumes the role of the DR without needing a fresh election process. This failover mechanism ensures continuous OSPF operation and prevents routing interruptions in the broadcast network.

Option A correctly describes this function. The BDR does not handle load balancing (which eliminates B), nor does it assign IP addresses (which removes C). IP addressing is handled by DHCP or static configuration, not by OSPF roles. Similarly, D is incorrect because external routing updates to non-OSPF networks are typically managed by Autonomous System Boundary Routers (ASBRs), not the BDR.

For the H12-821 exam, understanding this failover behavior and the election process between DR and BDR is fundamental. Candidates should be familiar with the election criteria, such as OSPF priority and router ID, and how these roles influence network scalability and stability. Mastery of these concepts will help ensure success on exam questions related to OSPF operation and network design principles.