Huawei Updated H12-821_V1.0 Exam Questions and Answers by klay

Let’s analyze the process step-by-step:

R1redistributes thedirect route 10.1.1.0/24intoOSPF.

This OSPF route reachesR2andR3.

R2 and R3 are in an environment that usesIS-IStowardsR4.

BothR2 and R3 re-advertisethis OSPF route into IS-IS toward R4 (bidirectional route redistribution).

OnR3, aroute-policy named hcipis applied to controlASE (Autonomous System External) route preference.

The ACL matches the route10.1.1.0/24.

The route-policy sets thepreferenceof this ASE route to14.

InHuawei VRP, if a route-policy applied via preference ase route-policy matches a route, itmodifies the preferencevalue of the redistributed route when it is advertised.

By default:

OSPF ASE routeshave apreference of 150.

But in this case, due to the policy applied, the preference is explicitly changed to14on R3 before re-advertising to R4.

So,R4will install the route10.1.1.0/24from R3 withpreference 14, assuming R2 doesn’t provide a better preference.

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

“You can control the preference of OSPF ASE routes by using a route-policy and applying it with the command preference ase route-policy. When the policy matches, the specified preference is used instead of the default (150).”

(Chapter: OSPF Advanced Features – Section: Route Control and Inter-AS Route Redistribution)

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).

Comprehensive and Detailed in-depth Step-by-Step Explanation:

AnArea Border Router (ABR)is an OSPF router that connects multiple areas, including the backbone area (Area 0). It plays a critical role in summarizing and propagating routing information between areas. The types of LSAs that an ABR can generate include:

Network Summary LSA (Type 3):

ABRs generate Type 3 LSAs to summarize and propagate routes from one area into another.

For example, an ABR generates a Type 3 LSA to inform other areas about the networks in the area it is connected to.

ASBR Summary LSA (Type 4):

If an ASBR exists in one of the OSPF areas connected to the ABR, the ABR generates Type 4 LSAs.

These LSAs provide information about how to reach the ASBR.

NSSA LSA (Type 7):

If the ABR is connected to a Not-So-Stubby Area (NSSA), it can generate Type 7 LSAs.

These LSAs are used to describe external routes imported into the NSSA.

AS External LSA (Type 5):

These LSAs are not typically generated by an ABR unless the ABR is also functioning as an ASBR. Type 5 LSAs are used to describe external routes imported into OSPF from other autonomous systems.

Therefore,NSSA LSA (A),Network Summary LSA (C), andASBR Summary LSA (D)are valid answers.AS External LSA (B)would only be correct if the ABR were also functioning as an ASBR, but that is not explicitly stated in the question.

Comprehensive and Detailed In-Depth Explanation:

Router LSAs (Type 1 LSAs)are generated byevery OSPF routerto describe itsdirectly connected linksand their states.

TheE (External) bitin theOptions fieldof a Type 1 LSA indicates whether the router is acting as anAutonomous System Boundary Router (ASBR).

IfE = 1, it means that the router is anASBR, which means it is redistributing external routes (e.g., BGP, static routes) into OSPF.

IR (Internal Router),ABR (Area Border Router), andDR (Designated Router)do not set theE-bitin their Router LSA unless they are also ASBRs.

????Reference:Huawei HCIA-Datacom Study Guide, OSPF Router Types and LSA Options.