Huawei H12-821 Practice Test Questions, Exam Dumps

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H12-821 Huawei Practice Test Questions and Exam Dumps

Question No 1:

To prevent inter-area routing loops, OSPF does not allow advertising routing information between two non-backbone areas and allows advertising routing information only within an area or between the backbone area and a non-backbone area.

Therefore, each ABR must be connected to the backbone area.

A. TRUE
B. FALSE

Answer: A. TRUE

Explanation:

Open Shortest Path First (OSPF) is a link-state routing protocol used in large enterprise networks. It divides the network into areas to improve scalability and reduce the size of the routing table. The OSPF protocol design incorporates a backbone area, known as Area 0, to ensure that routing information is exchanged efficiently across areas and to avoid routing loops.

OSPF follows the following rules to prevent inter-area routing loops:

Routing Information Between Non-Backbone Areas: OSPF does not allow routing information to be directly exchanged between non-backbone areas. This would lead to routing loops because there would be no clear path for routing information between these areas without going through the backbone.
Advertising Routing Information: OSPF allows routing information to be advertised within a single area or between the backbone (Area 0) and a non-backbone area. This ensures that all routing information flows through the backbone, making routing predictable and preventing loops.
ABRs (Area Border Routers): ABRs are routers that connect different OSPF areas. To ensure that routing information can flow correctly between areas, every ABR must be connected to Area 0 (the backbone area). Without this connection, routing information would not be able to flow properly between the non-backbone areas and the backbone, resulting in a disjointed OSPF network and routing issues.

In conclusion, each ABR must be connected to the backbone area (Area 0) to ensure that OSPF can function properly and prevent inter-area routing loops, making the statement TRUE.

Question No 2:

Which of the following statements regarding OSPF packets is false?

A. DD packets contain all LSA information and can be used to periodically synchronize LSDB information between neighbors.
B. Hello packets are used to discover and maintain OSPF neighbor relationships and also can be used to elect DR and BDR on broadcast and NBMA networks.
C. Two routers must send Hello packets at the same interval. Otherwise, they cannot establish an OSPF neighbor relationship.
D. DD packets carry LSA header information to describe link state summary information.

Answer: A

Explanation:

To understand why option A is false, let’s examine each statement in detail:

A. DD packets contain all LSA information and can be used to periodically synchronize LSDB information between neighbors.
This statement is false. DD (Database Description) packets in OSPF do not contain all LSA information. Instead, they only contain LSA headers, which provide a summary of the link-state information. These headers are used to initiate a conversation between OSPF neighbors about the link-state information they have. The full details of the LSAs are exchanged later using LSR (Link-State Request) and LSU (Link-State Update) packets. DD packets are used to synchronize the Link-State Database (LSDB), but they do not carry the full LSA details as suggested in option A.
B. Hello packets are used to discover and maintain OSPF neighbor relationships and also can be used to elect DR and BDR on broadcast and NBMA networks.
This statement is true. Hello packets are indeed used for establishing and maintaining OSPF neighbor relationships. Additionally, on broadcast and NBMA (Non-Broadcast Multiple Access) networks, Hello packets play a role in electing the Designated Router (DR) and Backup Designated Router (BDR).
C. Two routers must send Hello packets at the same interval. Otherwise, they cannot establish an OSPF neighbor relationship.
This statement is true. For two routers to form an OSPF neighbor relationship, they must agree on certain parameters, including the Hello interval (the frequency at which Hello packets are sent) and the Dead interval (how long to wait without receiving Hello packets before declaring the neighbor dead). If these intervals do not match, the routers will not establish a neighbor relationship.
D. DD packets carry LSA header information to describe link state summary information.
This statement is true. As mentioned earlier, DD packets carry LSA headers, which describe a summary of the link-state information. These headers are used to determine which LSAs need to be exchanged between OSPF neighbors in order to synchronize their Link-State Databases.

In summary, option A is false because DD packets do not contain all LSA information but rather only the LSA headers, making it the correct answer.

Question No 3:

Which of the following statements regarding OSPF neighbor relationship and adjacency is true?

A. Not all neighbors can establish adjacencies.
B. Neighbor relationships are selected from adjacencies to exchange routing information.
C. OSPF routers must establish an adjacency before exchanging information.
D. Adjacencies are maintained using OSPF DD packet.

Answer: A

Explanation:

OSPF (Open Shortest Path First) is a link-state routing protocol that relies on forming neighbor relationships and adjacencies between routers. Understanding the difference between neighbors and adjacencies, and knowing when and how OSPF routers exchange information, is key to interpreting the statements correctly. Let’s evaluate each option:

A. Not all neighbors can establish adjacencies:
This statement is true. In OSPF, a neighbor is a router that shares a common network segment and can potentially establish an adjacency, but not all neighbors will become full adjacencies. Adjacency is a formal relationship where two routers synchronize their link-state databases. OSPF routers may only form adjacencies with specific types of neighbors. For example:

On broadcast and non-broadcast multi-access networks (like Ethernet), routers will form full adjacencies with routers in the same area.
On point-to-point links, the routers will typically form an adjacency.
In some cases, routers on a multi-access network may form an adjacency only with the Designated Router (DR) and Backup Designated Router (BDR).

This statement acknowledges that not all neighbors will become full adjacencies, as it depends on the network type and OSPF configuration.

B. Neighbor relationships are selected from adjacencies to exchange routing information:
This statement is incorrect. It suggests the wrong relationship between neighbors and adjacencies. Neighbor relationships are the precursor to adjacencies, not the other way around. Routers exchange routing information once they form an adjacency, not by selecting neighbors from existing adjacencies. The correct process is that adjacencies are formed after establishing a neighbor relationship, and then routers exchange OSPF routing information through these adjacencies.

C. OSPF routers must establish an adjacency before exchanging information:
This statement is partially true but misleading. OSPF routers do exchange routing information as part of the neighboring process, even before fully establishing an adjacency. However, to exchange complete link-state information and fully synchronize their databases, routers must establish an adjacency. In summary, some exchange of routing information can occur before a full adjacency is formed (during the neighbor relationship phase), but full database synchronization (exchanging all link-state information) happens only once adjacencies are established.

D. Adjacencies are maintained using OSPF DD packet:
This statement is incorrect. OSPF DD (Database Description) packets are used during the initial stages of the OSPF adjacency formation process to describe and compare link-state databases between neighboring routers. While DD packets are part of the process of establishing an adjacency, they are not used to maintain an existing adjacency. Once the adjacency is established, hello packets and LSA (Link-State Advertisement) exchanges are used to maintain the relationship.

In conclusion, the correct answer is A. Not all neighbors can establish adjacencies, as it accurately reflects the OSPF behavior that not every router neighbor will necessarily become an adjacency.

Question No 4:

Which of the following statements regarding different LSA types is false?

A. LS Update packets contain complete LSA information.
B. LS Ack packets contain complete LSA information.
C. LS Request packets contain only LS Type, LS ID, and Advertising Router.
D. DD packets contain only LSA summary information, including LS Type, LS ID, Advertising Router, and LS Sequence Number.

Answer: B

Explanation:

In OSPF (Open Shortest Path First), Link State Advertisements (LSAs) are used to exchange routing information between OSPF routers. The different OSPF packet types (LSA Update, LS Acknowledgment, LS Request, and Database Description packets) are used to convey various aspects of LSA information, and it's important to understand what each type contains.

Let’s break down each option to understand why B is false:

A. LS Update packets contain complete LSA information: This statement is true. LS Update packets are used to actually send the link state advertisement (LSA) data. They contain the complete LSA information, including the details of the LSAs (like the link states, the router's topology, etc.), which other routers need to update their routing tables.
B. LS Ack packets contain complete LSA information: This statement is false. LS Acknowledgment (LS Ack) packets do not contain the complete LSA information. Instead, they are used to acknowledge the receipt of LS Update packets. The purpose of an LS Ack is simply to confirm that a router has received an LSA, ensuring reliable delivery, but it does not carry the actual routing information contained in the LSA. Thus, they do not contain the complete LSA data.
C. LS Request packets contain only LS Type, LS ID, and Advertising Router: This statement is true. LS Request packets are used by OSPF routers to request specific LSAs from other routers when they need information that they do not have in their database. These packets contain minimal information — specifically, the LS Type, LS ID, and Advertising Router — to specify which LSA is being requested.
D. DD packets contain only LSA summary information, including LS Type, LS ID, Advertising Router, and LS Sequence Number: This statement is true. Database Description (DD) packets are used during OSPF's database exchange process to summarize the LSAs that are present in the router's database. They do not carry full LSA data but instead contain a summary of the LSAs, including the LS Type, LS ID, Advertising Router, and LS Sequence Number, allowing routers to quickly compare and exchange information about their LSA databases.

LS Update packets contain the complete LSA information.
LS Ack packets are only acknowledgments and do not contain LSA information.
LS Request packets contain minimal LSA-related information (LS Type, LS ID, and Advertising Router).
DD packets contain LSA summary information.

Therefore, the false statement is B, as LS Ack packets do not contain complete LSA information.

Question No 5:

Which cost types are supported in IS-IS? (Choose 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 supports multiple types of cost metrics for calculating the best path through a network. These cost types define how the protocol evaluates the path cost to reach a destination.

Here’s a breakdown of the supported cost types:

A. Default: This is the most commonly used cost type in IS-IS. The default cost is typically used as the metric for path selection when no other special cost is specified. This is the standard metric that IS-IS uses to calculate the best path based on the available link costs.
B. Wide: The wide metric is used in IS-IS for wide metrics or extended metrics, which allow for larger metric values than the default. This is especially useful when the network requires more granularity in metric values. It was introduced to accommodate networks with higher bandwidth links and the need for larger metric ranges.
D. Narrow: The narrow metric is the traditional metric that IS-IS uses, which is limited to a smaller range (1-63). This metric type was originally used in older IS-IS implementations and networks. Narrow metrics are still supported in modern versions of IS-IS, but they are less commonly used because the wide metric is preferred for larger networks.

Why C. ToS is incorrect:

C. ToS (Type of Service) is not a cost type directly used in IS-IS routing protocol for path selection. While IS-IS does support traffic engineering and can be extended to accommodate traffic classes based on ToS, the ToS field is not typically used as a cost type in standard IS-IS operations. The Type of Service is more commonly associated with IP routing protocols and QoS (Quality of Service) features rather than being a cost metric in IS-IS.

In conclusion, default, wide, and narrow are valid cost types supported in IS-IS, while ToS is not. Therefore, the correct answers are A, B, and D.

Question No 6:

Which of the following statements about IS-IS Hello packets are true? (Choose all that apply.)

A. Level-1 LAN IIH packets do not contain the System ID field.
B. P2P IIH packets and LAN IIH packets are exactly the same.
C. P2P IIH packets do not contain the Priority field.
D. Level-1 LAN IIH packets are sent in multicast mode.

Answer: C and D

Explanation:

IS-IS (Intermediate System to Intermediate System) is a link-state routing protocol used in large networks for efficient routing. It uses Hello packets (also known as IIH or Intermediate System Hello) to establish and maintain neighbor relationships between routers. These Hello packets vary slightly depending on whether they are sent on a Point-to-Point (P2P) link or a LAN. Let’s break down each statement to determine which are true.

A. Level-1 LAN IIH packets do not contain the System ID field.

This statement is false. The System ID is part of the IIH packets for both Level-1 and Level-2 routers in IS-IS. The System ID is essential because it uniquely identifies each router within the IS-IS routing domain. In Level-1 LAN IIH packets, the System ID is included and used for neighbor discovery, so the statement that it is absent in Level-1 LAN IIH packets is incorrect.

B. P2P IIH packets and LAN IIH packets are exactly the same.

This statement is false. There are differences between P2P (Point-to-Point) and LAN (Local Area Network) IIH packets.

P2P IIH packets are designed for direct communication between two routers, so they have a simpler structure.
LAN IIH packets are used in a multi-access network and contain more fields (for example, the LAN Priority field), which allow routers to negotiate and establish relationships in a broadcast or multi-access network.

Hence, P2P and LAN IIH packets are not exactly the same and differ in how they handle certain fields, like the Priority field, and their multicast behavior.

C. P2P IIH packets do not contain the Priority field.

This statement is true. The Priority field is included in LAN IIH packets, but not in P2P IIH packets. In P2P links, there's no need for a priority field because there are only two routers exchanging Hello packets directly, whereas, in LANs, multiple routers could potentially compete to become the Designated Router (DR), so the Priority field is used to determine which router should take on that role.

D. Level-1 LAN IIH packets are sent in multicast mode.

This statement is true. Level-1 LAN IIH packets are indeed sent using multicast mode. Specifically, these packets are sent to the All IS-IS Routers multicast address 224.0.0.13. This is necessary for all routers on the network to listen for Hello packets and establish neighbor relationships. In contrast, P2P IIH packets are sent unicast, since they are exchanged between only two routers.

C. P2P IIH packets do not contain the Priority field is true because the Priority field is not needed for point-to-point communication.
D. Level-1 LAN IIH packets are sent in multicast mode is true because LAN IIH packets are multicast to allow multiple routers on the LAN to receive them.

Question No 7:

Two Level-1 routers in different areas can establish a neighbor relationship.

A. TRUE
B. FALSE

Answer: B

Explanation:

In OSPF (Open Shortest Path First) routing, Level-1 routers are used in OSPF areas for intra-area routing. For two OSPF routers to establish a neighbor relationship, they need to be in the same area. Level-1 routers are specifically designed to communicate within a single OSPF area, and they do not establish neighbor relationships across different areas.

OSPF Areas are designed to optimize routing by reducing the size of the routing table and limiting the scope of routing updates. A router in one area (Level-1 router) cannot establish a Level-1 relationship with a router in another area because OSPF neighbor relationships for Level-1 are confined to the same area.
If routers are in different areas, they would establish a Level-2 neighbor relationship (used for inter-area communication). In this case, a ABR (Area Border Router) connects the Level-1 routers in different areas and handles the communication between them by advertising inter-area routes.

Therefore, two Level-1 routers in different areas cannot establish a neighbor relationship, making Option B (FALSE) the correct answer.

Question No 8:

Which of the following attributes must be carried in an Update message?

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

Correct Answer: C

Explanation:

In BGP (Border Gateway Protocol), an Update message is used to advertise network reachability information to neighboring routers. This message includes important routing information, including various attributes that determine the best path for data transmission. Let’s review each option to understand which attributes are mandatory in an Update message.

A. local-Pref: This is not mandatory in every BGP Update message. The local-preference (local-Pref) attribute is used within an AS (Autonomous System) to prioritize outbound routes. However, it is optional and is only carried in an Update message if it is explicitly configured or necessary for route selection.
B. MED: The Multi-Exit Discriminator (MED) is used to influence route selection when multiple exit points are available from an AS. It is also optional and is not required to be carried in every BGP Update message. The MED attribute can be included if it is needed for route advertisement.
C. AS_Path: The AS_Path attribute is mandatory in BGP Update messages. This attribute lists the ASs that a route has traversed. It is crucial for preventing routing loops and helping to determine the shortest path. The AS_Path is carried in every BGP Update message to indicate the path the route has taken across multiple ASs, making it a fundamental part of BGP routing.
D. PrefVal: This is not a standard BGP attribute. It seems to be either a hypothetical or non-standard attribute. In BGP, local-preference is often used for internal path preference, but "PrefVal" does not appear to be a recognized attribute in standard BGP operation.

In summary, the AS_Path attribute (C) is required in BGP Update messages, making it the correct answer. It helps ensure loop-free routing and allows routers to make informed routing decisions based on the AS path.

Question No 9:

Which of the following statements best describes the function of OSPF's Designated Router (DR) on a broadcast network?

A) It forwards packets to external networks.
B) It reduces the number of OSPF adjacencies required.
C) It performs NAT translations for internal hosts.
D) It assigns IP addresses to connected devices.

Correct Answer: B) It reduces the number of OSPF adjacencies required.

Explanation:

In the context of Huawei’s H12-821 HCIP-Datacom-Core Technology certification, a strong understanding of OSPF (Open Shortest Path First) behavior, particularly in broadcast and multi-access networks, is crucial. The concept of the Designated Router (DR) is pivotal in reducing OSPF overhead and improving routing efficiency in environments such as Ethernet LANs. On a broadcast network, every OSPF router would ideally need to form an adjacency with every other router, which results in a large number of adjacencies. For example, with five routers, ten separate adjacencies are required. This can lead to excessive use of network and CPU resources.

To mitigate this issue, OSPF elects a Designated Router (DR) and a Backup Designated Router (BDR). The DR serves as a central point of communication for OSPF routers on the segment. Instead of each router forming a full adjacency with all others, they only form adjacencies with the DR and BDR. This reduces the number of adjacencies significantly—from a potential n(n–1)/2 to just 2n–2—thereby enhancing scalability and reducing protocol chatter.

The DR is responsible for generating LSAs (Link State Advertisements) on behalf of the network, which improves synchronization of routing tables among routers. It also simplifies the flooding process, as LSAs are sent only to the DR, which then redistributes them to all other routers. The BDR takes over if the DR fails, ensuring redundancy. This election process is determined by the OSPF router priority value and, in the case of a tie, the router ID.

Understanding this mechanism is critical in both the theoretical and practical components of the H12-821 exam. Huawei’s Datacom certification emphasizes deep comprehension of routing technologies such as OSPF, BGP, and ISIS, all of which form the foundation for configuring and optimizing modern enterprise networks. Mastery of these concepts not only helps pass the exam but also equips professionals to handle real-world scenarios in large-scale network design. Practice tests and exam dumps often include nuanced questions about the OSPF DR/BDR mechanism, router state transitions, and LSA propagation, making it essential for candidates to grasp both the high-level idea and the detailed operational behavior of these routing components.