Free Huawei H12-831_V1.0 Practice Exam with Questions & Answers | Set: 7

Comprehensive and Detailed In-Depth Explanation:

To determine which statement is false, we need to analyze the IS-IS topology, the role of multi-topology, the IPv6 summary configuration, and the level-1-2 behavior of IS-IS routers. Let’s break it down step by step:

Understanding the IS-IS Topology and Levels:

IS-IS supports multiple levels: Level-1 (L1) for intra-area routing, Level-2 (L2) for inter-area routing, and Level-1-2 (L1-2) routers that can operate in both levels and connect L1 and L2 areas.

In the figure, R1 and R2 are configured as Level-1-2 routers, R3 is a Level-1-2 router, R4 is a Level-1 router, and R5 is a Level-1 router. The area borders are indicated by the system IDs (49.0001 for R4’s area and 49.0002 for R3 and R5’s area).

R4’s Loopback0 has the IPv6 address 2000::/128, which is a host route (a /128 prefix, representing a single address).

Multi-Topology IS-IS for IPv6:

Multi-topology IS-IS allows separate topologies for IPv4 and IPv6, ensuring that IPv6 routes are handled independently. Since multi-topology is enabled on all routers, IPv6 routes (like 2000::/128 on R4) are advertised and processed within the IPv6 topology.

This means that IPv6 routes, including the Loopback0 address of R4 (2000::/128), can be advertised across the IS-IS domain, subject to the level and summary configurations.

IPv6 Summary Configuration (2000::/64 level-1-2):

The command ipv6 summary 2000::/64 level-1-2 is configured in the IS-IS processes of R1 and R2. This command instructs R1 and R2 (as Level-1-2 routers) to summarize the IPv6 prefix 2000::/64 and advertise it to both Level-1 and Level-2 areas.

Summarization means that instead of advertising the more specific route (e.g., 2000::/128 from R4), R1 and R2 advertise the less specific summary route 2000::/64. This summary route covers the 2000::/128 address of R4’s Loopback0.

Since R1 and R2 are Level-1-2 routers, they can advertise this summary to both their Level-1 neighbors (like R4 and R3) and Level-2 neighbors (across areas).

Analyzing Each Statement:

A. The routing table of R1 contains the route 2000::/64.

True. R1 is a Level-1-2 router with the ipv6 summary 2000::/64 level-1-2 command configured. It advertises and installs the summary route 2000::/64 in its routing table, covering the more specific 2000::/128 from R4. Additionally, as a Level-1-2 router, R1 can learn and retain this route from its IS-IS neighbors.

B. The routing table of R2 contains the route 2000::/64.

True. Similar to R1, R2 is also a Level-1-2 router with the same summary command. It advertises and installs the 2000::/64 summary route in its routing table, covering R4’s 2000::/128.

C. The routing table of R3 contains the route 2000::/128.

False. R3 is a Level-1-2 router in area 49.0002, but it receives routes from R2 (a Level-1-2 router in area 49.0001). Because R1 and R2 are configured with the ipv6 summary 2000::/64 level-1-2 command, they advertise the summary route 2000::/64 to their neighbors, including R3. IS-IS prefers the most specific route, but the summary configuration ensures that the more specific 2000::/128 from R4 is not advertised beyond R1 and R2 unless explicitly allowed. Since R3 is in a different area and receives the summary 2000::/64 from R2, it does not have the more specific 2000::/128 route in its routing table. Therefore, this statement is false.

D. The routing table of R2 contains the route 2000::/128.

True. R2, as a Level-1-2 router, is directly connected to R4 (a Level-1 router) via the IS-IS topology. R4 advertises its Loopback0 address 2000::/128 to R2. Even though R2 is configured to summarize 2000::/64, it can still retain the more specific 2000::/128 route in its routing table because IS-IS allows routers to keep both summary and more specific routes, with the more specific route taking precedence for routing decisions.

Conclusion:

The false statement is C, as R3 does not contain the route 2000::/128 in its routing table. Instead, R3 receives the summary route 2000::/64 from R2 due to the summary configuration on R1 and R2.

References to HCIP-Datacom-Advanced Routing & Switching Technology Documents:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0, Section on IS-IS: Multi-Topology IS-IS for IPv6, Level-1 and Level-2 Operations, and Route Summarization.

HCIP-Datacom-Advanced Routing & Switching Technology V1.0, Chapter on IPv6 Routing Protocols: IS-IS Configuration and Behavior, Including Summary Address Commands and L1/L2 Interactions.

Comprehensive and Detailed In-Depth Explanation:

To determine the correct answer, we need to analyze how each command impacts OSPF neighbor relationships.

1. Understanding OSPF Neighbor Formation

OSPF routers form neighbor relationships when they meet the following conditions:

They are in the same subnet (IP addresses and subnet masks must match).

They are in the same OSPF area.

They use the same network type (e.g., Broadcast, Point-to-Point).

Authentication (if configured) must match.

Hello and Dead timers must match.

2. Analyzing Each Answer Option

❌ A. " undo ip address 10.0.12.2 24 " → Affects OSPF Neighbor Status

Removing the IP address will prevent the interface from sending and receiving OSPF Hello packets.

Without an IP address, OSPF cannot establish neighbor relationships.

Effect: Breaks OSPF neighbor status.

✅ B. " undo description " → Does NOT Affect OSPF Neighbor Status

The interface description is just a label for administrators and has no impact on OSPF functionality.

It does not affect neighbor relationships, routing, or communication.

Effect: No impact on OSPF neighbors.

❌ C. " undo ospf cost " → Affects OSPF Neighbor Status Indirectly

OSPF cost determines the path selection but does NOT break the neighbor relationship.

However, if the cost change leads to routing table recalculations, it might cause temporary convergence issues.

Effect: Does not directly break neighbor status, but affects route selection.

❌ D. " undo ospf dr-priority " → Affects OSPF Neighbor Status (Possibly Causes DR Re-Election)

OSPF DR/BDR election uses priority values.

If changed, a new election might occur, leading to a temporary loss of neighbor relationships.

Effect: Might cause OSPF neighbor reset (temporary impact on adjacency).

✅ Explanation:

???? Network Summary:

IS-IS (IPv6) runs on: R2 ⇄ R3 ⇄ R6

R6 owns Loopback0 = 2000::6/128

OSPFv3 runs on: R1, R2, R3, R4, R5

Area 1 = Stub (R4), Area 2 = NSSA (R5)

Redistribution: IS-IS → OSPFv3 happens on R2 and R3

???? Option A: R5 contains 2000::6/128

✅ True

Area 2 is NSSA, and by default:

External routes (like IS-IS) imported via import-route isis on R3 become Type-7 LSAs

Then translated to Type-5 LSAs by R3 (ABR) for other areas.

R5 will receive the translated route.

???? Option B: R1 contains 2000::6/128

✅ True

R2 and R3 redistribute the IS-IS IPv6 route into OSPFv3.

R1 is in Area 0, directly connected to both R2 and R3.

It receives the route as a normal OSPFv3 inter-area (Type-3) or external (Type-5) route.

???? Option C: R6 contains ::/0 (default route)

❌ False

R6 runs IS-IS Level-1 only.

IS-IS Level-1 routers do not automatically get a default route.

To get a default route in Level-1, the ABR must explicitly advertise it using:

pgsql

CopyEdit

isis default-route advertise always level-1

No such configuration is mentioned → R6 does not receive ::/0 by default.

???? Option D: R4 contains 2000::6/128

✅ True

R4 is in Area 1 (Stub).

Stub areas block Type-5 LSAs but allow Type-3 (inter-area) LSAs.

Since IS-IS → OSPF redistribution occurs into backbone (Area 0), and R4 connects to it via R2 (ABR), R4 will receive the route via a Type-3 LSA.

✅ Final Answer: A, B, D

Official Huawei Extract:

" In OSPFv3, NSSA areas allow Type-7 LSAs, which are converted to Type-5 LSAs by the ABR. Stub areas block external LSAs but allow inter-area (Type-3) LSAs. IS-IS Level-1 routers require explicit default-route injection to receive ::/0. "

— [Huawei HCIA-Datacom Guide – IS-IS and OSPFv3 Redistribution and Area Behaviors]

Comprehensive and Detailed In-Depth Explanation:

Understanding the BGP and IS-IS Network Topology in the Question:

IS-IS Areas:

Area 49.0001 (Level-1 IS-IS): R1, R2, R4, R5.

Area 49.0002 (Level-2 IS-IS): R3, R6.

R2 acts as an ABR (Area Border Router) and redistributes routes between Level-1 and Level-2 using import-route isis level-2 into level-1.

BGP Route Reflection & Peering:

R2 and R5 are Route Reflectors (RRs).

iBGP peering is established among all routers (R1, R2, R3, R4, R5, R6).

R1 and R4 import 192.168.1.0/24 into BGP, meaning this prefix will be advertised to all iBGP peers.

R3 and R6 import 192.168.2.0/24 into BGP, meaning this prefix will also be advertised to all iBGP peers.

Route Distribution Analysis:

Route to 192.168.1.0/24 (Imported by R1 & R4):

R1 and R4 advertise 192.168.1.0/24 into iBGP.

Since R2 and R5 are Route Reflectors (RRs), they will reflect these routes to all their iBGP clients (R1, R3, R4, R6).

R2 learns two valid routes to 192.168.1.0/24 (from R1 and R4).

R5, as another RR, learns both routes and advertises them as well.

R2 ultimately has three valid paths (direct from R1 and R4, plus a reflected route from R5).✅ Statement C is correct: The BGP routing table of R2 contains three valid routes to 192.168.1.0/24.

R5 also learns 192.168.1.0/24 from both R1 and R4.✅ Statement B is correct: The BGP routing table of R5 contains two valid routes to 192.168.1.0/24 (from R1 and R4).

Route to 192.168.2.0/24 (Imported by R3 & R6):

R3 and R6 import 192.168.2.0/24 into BGP.

R2 and R5 (Route Reflectors) learn this route and reflect it to their clients (R1, R3, R4, R6).

R4 receives three valid paths (directly from R3 and R6 via BGP, and one additional reflected path via R5).✅ Statement D is correct: The BGP routing table of R4 contains three valid routes to 192.168.2.0/24.

Checking Statement A:

R3 originally imports 192.168.2.0/24 and advertises it.

Since it is a Route Reflector Client of R5 and R2, it should have multiple routes via iBGP, not just one.❌ Statement A is incorrect because R3 should have multiple valid routes, not just one.

Final Conclusion:

✅ B. The BGP routing table of R5 contains two valid routes to 192.168.1.0/24.

✅ C. The BGP routing table of R2 contains three valid routes to 192.168.1.0/24.

✅ D. The BGP routing table of R4 contains three valid routes to 192.168.2.0/24.

❌ A. The BGP routing table of R3 does NOT contain only one valid route to 192.168.2.0/24 (it has multiple routes).

Thus, the correct answers are: B, C, D.

Although network maintenance includes routine maintenance and troubleshooting, experience does not exempt maintenance personnel from following standardized operating guidelines.

Huawei requires maintenance personnel to comply strictly with operating and safety regulations. Maintenance work should include impact assessment, authorization, information collection, configuration or data backup, operation recording, fault verification, and preparation of recovery measures. These requirements apply even to highly skilled engineers because an undocumented or unauthorized operation can interrupt services or make recovery more difficult.

Therefore, the first part of the statement is acceptable, but the claim that experienced personnel may disregard operation guidelines makes the complete statement false. Huawei troubleshooting principles and maintenance precautions.

Comprehensive and Detailed In-Depth Explanation:

Understanding the BGP Network Topology in the Question:

BGP Peering & Route Distribution

Each router forms EBGP peer relationships with directly connected neighbors.

R1 and R4 import the static route 192.168.1.0/24 into BGP and advertise it to their peers.

Community attributes are attached to routes to influence routing policies.

Effect of Community Attribute 1:1

R1 marks 192.168.1.0/24 with community 1:1 before advertising it.

R3 has a policy that rejects any routes with community attribute 1:1.

Since R1’s advertisement contains 1:1, R3 will not accept 192.168.1.0/24 from R2.

Route Selection and Traffic Flow Analysis:

R1 advertises 192.168.1.0/24 with community 1:1 to R2.

R3 rejects this route from R2 because of the configured routing policy.

R4 also advertises 192.168.1.0/24 to its EBGP neighbors without community 1:1.

R5 learns the route from R4 and advertises it to R3.

Since R5’s advertisement does not include community 1:1, R3 accepts the route from R5.

Thus, the best available path for R3 to reach 192.168.1.0/24 is R3 → R5 → R1.

✅ Correct Path: R3 → R5 → R1

Checking Each Option:

❌ Option A: R3 → R2 → R4 (Incorrect)

R3 does not learn the route from R2 because it rejects community 1:1.

Since R1 added 1:1, and R2 propagated the same community, R3 will not accept this path.

❌ Option B: R3 does not have a route to 192.168.1.0/24 (Incorrect)

R3 does have a route, but it learns it from R5 instead of R2.

❌ Option C: R3 → R2 → R1 (Incorrect)

R1 marked the route with 1:1, and R2 advertised it with the same community.

Since R3 rejects 1:1 routes, it will not use this path.

✅ Option D: R3 → R5 → R1 (Correct)

R5 learns the route from R4, which does not have community 1:1, and advertises it to R3.

R3 accepts this route and forwards traffic to R5, which sends it to R1.

Final Conclusion:

✅ D. The correct path for traffic from R3 to 192.168.1.0/24 is R3 → R5 → R1.

Thus, the correct answer is: D.

The statement contains two material technical errors. The LSP Number field is one byte, or 8 bits, not 4 bits. An 8-bit field provides values from 0 through 255, allowing an IS-IS process to generate a maximum of 256 original LSP fragments for a system ID. Four bits would allow only 16 values and could not identify 256 fragments.

The statement also incorrectly says “a minimum of 256 LSP fragments.” The correct term is maximum: the process can generate up to 256 fragments under its normal system ID; it is not required to generate at least 256.

The final concept is correct: IS-IS LSP fragment extension permits additional system IDs to be configured. Each additional system ID provides space for another 256 extended LSP fragments, enabling the originating IS-IS process to advertise more link-state information.

Because a true/false statement must be correct in its entirety, the incorrect field length and “minimum” wording make the supplied statement false. The corrected version would state: “The LSP Number field is one byte long, allowing a maximum of 256 LSP fragments per system ID.” Huawei IS-IS LSP Fragment Extension