Free Huawei H12-821_V1.0 Practice Exam with Questions & Answers | Set: 2

BFD operates at the network layer, providing rapid fault detection for forwarding paths, such as IP routing and MPLS tunnels. It interacts closely with network protocols (e.g., OSPF, BGP) to ensure high reliability and quick response to faults. BFD does not belong to the application, data link, or physical layers but functions as a network layer diagnostic tool as confirmed in Huawei's network protocol training ​.

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Explanation of Root Port Election in STP:

In a Spanning Tree Protocol (STP) network, theRoot Portis selected on each switch (except the Root Bridge). The Root Port is the port with thelowest path costto the Root Bridge. If there is a tie in path cost, the following criteria are used in sequence to break the tie:

Steps for Root Port Election in Sequence:

RPC Comparison (Root Path Cost):

The port with thelowest Root Path Costis preferred.

Root Path Cost is the cumulative cost of the path to the Root Bridge.

Peer BID (Bridge ID) Comparison:

If the Root Path Costs are equal, theBridge IDof the connected switch (peer) is compared.

The port connecting to the switch with thelower Bridge IDis preferred.

Peer PID (Port ID) Comparison:

If the Bridge IDs are equal, thePort IDof the peer's sending port is compared.

The port connecting to thelower Port IDis preferred.

Local PID (Port ID) Comparison:

If all else is equal, theLocal Port IDof the switch is used.

The port with thelower Local Port IDis selected.

After Layer 3 roaming, the STA’s traffic is forwarded from the Foreign AP (FAP) to the Foreign AC (FAC), and then to the Home AC (HAC) before reaching the upper-layer network. This ensures that the STA remains on the same subnet without breaking existing sessions ​.

Comprehensive and Detailed Step-by-Step Explanation:

Analysis of the OSPF Neighbor State:

Router ID 10.0.5.5:

On interface 10.0.235.2 (GigabitEthernet0/0/1), the neighbor state is Full, indicating that adjacency is established.

The Designated Router (DR) is 10.0.235.5, which is the same as the neighbor's address.

Router ID 10.0.4.4:

On interface 10.0.24.2 (Serial1/0/1), the neighbor state is also Full, meaning adjacency is established.

The DR/BDR election status shows None, indicating that the interface is on a point-to-point link where DR/BDR election does not apply.

Validation of Each Option:

Option A: Correct. The DR IP address is explicitly shown as 10.0.235.5.

Option B: Correct. The neighbor state for both 10.0.5.5 and 10.0.4.4 is Full, confirming adjacency is established.

Option C: Incorrect. DR/BDR elections are irrelevant on point-to-point links like Serial1/0/1.

Option D: Correct. The Router IDs of R2's neighbors are explicitly listed as 10.0.5.5 and 10.0.4.4.

The output shows that the router with the IP10.0.12.2is the Backup Designated Router (BDR), as indicated in theState: BDRfield. The router ID is10.0.2.2, the interface cost is 1, and the IP address of the interface is10.0.12.2. Hence, C is the correct answer ​.

Understanding DIS Election in IS-IS:

On an IS-IS broadcast network, aDesignated Intermediate System (DIS)is elected to create and update pseudonodes for efficient communication.

The election is based on the following criteria:

DIS Priority:The router with the highest priority is elected as the DIS.

Router ID (tie-breaker):If priorities are equal, the router with the highest Router ID is elected.

Analyzing the DIS Priorities and Router IDs:

R1: Priority = 64, Router ID = 1.1.1.1

R2: Priority = 1, Router ID = 2.2.2.2

R3: Priority = 127, Router ID = 3.3.3.3

R4: Priority = 10, Router ID = 4.4.4.4

Among the routers,R3 has the highest DIS priority (127), making it the DIS.

Correct Option:

Option B (R3):Correct, as R3 has the highest priority.

Option A (R1):Incorrect, as its priority is lower (64).

Option C (R4):Incorrect, as its priority is lower (10).

Option D (R2):Incorrect, as its priority is the lowest (1).

In BGP and other TCP-based protocols like OSPF and IS-IS, when devices havedifferent Hold Times, thesmaller value is chosenafter negotiation. This ensuresfaster detectionof communication loss.

The Keepalive and Hold Timers are negotiated during the establishment of a BGP session.

The smaller Hold Timeis used to maintain symmetry and prevent timeouts.

Reference from Huawei HCIP-Datacom-Core Technology Study Guide:

“When negotiating Hold Time, both ends agree to use the smaller of the two values. This value is used to detect failures faster.”

(Chapter: BGP Fundamentals – Section: BGP Session Establishment)

An OSPF AS-external LSA is used to describe routes to networks that are external to the OSPF Autonomous System (AS). This external route information is typically imported into OSPF by anAutonomous System Boundary Router (ASBR).

If theForwarding Addressfield in the AS-external LSA is set to 0.0.0.0, this indicates that traffic destined for the external network should be forwarded directly to the ASBR that advertised the external route.

The specific context mentioned here relates to theNot-So-Stubby Area (NSSA), a type of OSPF area designed to handle AS-external routes in a more controlled way. In NSSAs:

Type 7 LSAs are used to describe AS-external routes.

The ASBR within the NSSA converts the Type 7 LSA to a Type 5 LSA before advertising it to the backbone area.

Hence, the correct acronym for the described functionality isNSSA.

Comprehensive and Detailed In-Depth Explanation:

NET (Network Entity Title)is a special form ofNSAP (Network Service Access Point)used inIS-IS routing.

NET consists of three fields:

AFI (Authority and Format Identifier) + IDI (Initial Domain Identifier) + Area Address→ Identifies thearea.

System ID→ Uniquely identifies arouter within an area(similar to an OSPF Router ID).

SEL (NSEL - N-selector)→ Always0in a NET, as IS-IS operates at Layer 3.

SinceSystem IDuniquely identifies ahost/router within an area, the correct answer isA.

????Reference:Huawei HCIA-Datacom Study Guide, IS-IS Addressing and NET Structure.

Understanding the LSDB and Level-2 DIS Election in IS-IS:

In IS-IS, theDesignated Intermediate System (DIS)is elected for both Level-1 and Level-2 on broadcast networks to manage the link-state database (LSDB) and reduce the number of LSAs exchanged.

The election of the DIS is based on thehighest priority. If the priority is the same, the router with thehighest System IDbecomes the DIS.

HCIP-Datacom-Core Technology Training Material (IS-IS DIS Election)​​.

Analyzing the LSDB:

From the LSDB ofR1, the Level-2 link-state database includes the following entries:

LSPID 0100.0000.3003.00-00: This is R3, and it is present in the Level-2 LSDB with the sequence number and checksum details.

Other routers (R1, R2, R4) are present but do not have the characteristics of the Level-2 DIS in this topology.

Based on the System IDs,R3 (0100.0000.3003)has the highest System ID, making it theLevel-2 DIS.

Conclusion:

The Level-2 DIS on the network isR3, based on the election rules and the LSDB information shown in the figure.