Free Huawei H12-831_V1.0 Practice Exam with Questions & Answers | Set: 2

Comprehensive and Detailed In-Depth Explanation:To determine whether the statement is true or false, we need to analyze the OSPF network, the cost values of the links, the primary and backup paths, and the role of OSPF IP Fast Reroute (FRR) enabled on R1. Let’s break it down step by step:

Understanding the Network Topology and Costs:

The network consists of four routers: R1, R2, R3, and R4.

The destination network is 10.0.3.3/32, located at R3.

The link costs are as follows:

R1 to R2: Cost = 10

R1 to R4: Cost = 10

R4 to R2: Cost = 20

R2 to R3: Cost = 5

The total cost of a path is the sum of the costs of all links in that path.

Calculating the Primary Path Cost (R1 -> R2 -> R3):

Path: R1 -> R2 (cost = 10) -> R3 (cost = 5)

Total cost = 10 + 5 = 15

This is the shortest path (lowest cost) from R1 to R3, as stated in the question. OSPF uses the Dijkstra algorithm to calculate the shortest path based on link costs, so R1 will naturally select R1 -> R2 -> R3 as the primary path to reach 10.0.3.3/32.

Calculating the Backup Path Cost (R1 -> R4 -> R2 -> R3):

Path: R1 -> R4 (cost = 10) -> R2 (cost = 20) -> R3 (cost = 5)

Total cost = 10 + 20 + 5 = 35

This path has a higher cost (35) compared to the primary path (15), which is expected for a backup path. The backup path is not used under normal conditions but is precomputed for fast failover in case the primary path fails.

Role of OSPF IP Fast Reroute (FRR):

OSPF IP FRR is a mechanism designed to provide fast convergence in case of link or node failures by precomputing backup paths. When enabled on R1, FRR ensures that R1 has a precomputed backup path to quickly switch traffic to an alternate route (e.g., R1 -> R4 -> R2 -> R3) if the primary path (R1 -> R2 -> R3) fails.

FRR typically uses Loop-Free Alternates (LFA) or other techniques to ensure the backup path does not create loops and is immediately available. In this case, the backup path R1 -> R4 -> R2 -> R3 is valid because:

It does not loop back to R1.

It reaches R3, the destination.

The cost (35) is higher than the primary path (15), but this is acceptable for a backup path.

The question states that OSPF IP FRR is enabled on R1, and the backup path is explicitly given as R1 -> R4 -> R2 -> R3. This aligns with FRR’s purpose of maintaining a precomputed backup path.

Verifying the Statement:

The statement claims: “The primary path from R1 to 10.0.3.3/32 is R1 -> R2 -> R3, and the backup path is R1 -> R4 -> R2 -> R3.”

We calculated that the primary path (R1 -> R2 -> R3) has a cost of 15, which is the shortest path and correct for OSPF’s behavior.

The backup path (R1 -> R4 -> R2 -> R3) has a cost of 35, which is higher but valid as a backup path, especially with OSPF IP FRR enabled on R1 to ensure fast failover.

Both paths are correctly identified in the question, and OSPF IP FRR’s presence on R1 supports the existence of a precomputed backup path. Therefore, the statement is accurate.

Conclusion:

The primary path (R1 -> R2 -> R3) and backup path (R1 -> R4 -> R2 -> R3) are correctly described, and OSPF IP FRR on R1 ensures the backup path is precomputed and ready for use. Thus, the statement is true.

References (Based on HCIP-Datacom-Advanced Routing & Switching Technology Concepts):

OSPF Path Calculation: HCIP-Datacom documentation on OSPF’s Dijkstra algorithm and cost-based path selection (e.g., Section on OSPF Routing Metrics).

OSPF IP Fast Reroute (FRR): HCIP-Datacom coverage of FRR mechanisms, including Loop-Free Alternates and backup path computation (e.g., Chapter on OSPF Advanced Features and High Availability).

Link Cost and Path Optimization: HCIP-Datacom explanation of link cost configuration and OSPF path selection (e.g., Section on OSPF Network Design and Optimization).

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1. Understanding VLAN Aggregation in Huawei Switches

VLAN aggregation is a technique that groups multiple VLANs (sub-VLANs) under a single Super-VLAN.

Super-VLANs do not have member interfaces but include multiple Sub-VLANs that share a common gateway (VLANIF interface).

2. Inter-Sub-VLAN Communication Requirement

By default, hosts in different sub-VLANs cannot communicate directly.

To enable communication between different sub-VLANs within the same Super-VLAN, an inter-sub-VLAN proxy must be enabled.

This is done using the inter-sub-vlan-proxy enable command in the VLANIF interface of the Super-VLAN.

3. Correct Command Usage

The command format is:

shell

CopyEdit

supervlan inter-sub-vlan-proxy enable

This command must be executed under VLANIF 10, corresponding to the Super-VLAN.

4. Why is the Answer "supervlan"?

The missing parameter in the command should be supervlan, because it is used to enable communication between Sub-VLANs under a Super-VLAN.

This is a specific Huawei command used in HCIP-Datacom-Advanced Routing & Switching Technology certification.

Comprehensive and Detailed In-Depth Explanation:

1. Understanding DHCP Snooping

DHCP Snooping is a security feature that filters untrusted DHCP messages to prevent attacks such as:

Rogue DHCP servers distributing incorrect IP addresses.

DHCP starvation attacks.

In DHCP Snooping, switch ports are classified as:

Trusted Interfaces: Allow both DHCP requests and DHCP responses to pass through.

Untrusted Interfaces: Allow only DHCP requests but drop DHCP responses (to prevent rogue DHCP servers).

2. Analyzing Each Answer Option

Option A: "When receiving a DHCP response packet on GE0/0/2, the switch forwards the packet through GE0/0/1."

Correct.

GE0/0/2 is a trusted interface (connected to the DHCP server).

DHCP responses (ACK, NAK, OFFER) come from the DHCP Server.

Since DHCP responses are allowed on trusted interfaces, the switch forwards them to the client (PC1) via GE0/0/1.

Option B: "When receiving a DHCP request packet on GE0/0/2, the switch forwards the packet through GE0/0/3."

Incorrect.

DHCP requests originate from clients (PC1, attackers, etc.), not from the DHCP server.

The DHCP request should be forwarded to the DHCP server via a trusted interface (not GE0/0/3, which is untrusted).

Option C: "When receiving a DHCP response packet on GE0/0/3, the switch forwards the packet through GE0/0/1."

Incorrect.

GE0/0/3 is an untrusted interface (connected to the attacker).

DHCP responses (ACK, OFFER) from untrusted interfaces are dropped to prevent rogue DHCP attacks.

The switch will not forward the packet.

Option D: "When receiving a DHCP request packet on GE0/0/3, the switch forwards the packet through GE0/0/2."

Correct.

DHCP requests originate from clients (PC1 or attacker).

Since DHCP requests are allowed on untrusted interfaces, the switch forwards them to the DHCP server via the trusted interface (GE0/0/2).

Final Answer:

✅ A and D are correct.

HCIP-Datacom-Advanced Routing & Switching Technology References:

DHCP Snooping and Port Trust Classification

How Trusted and Untrusted Ports Handle DHCP Packets

Preventing Rogue DHCP Servers Using DHCP Snooping

Comprehensive and Detailed In-Depth Explanation:

In MPLS (Multiprotocol Label Switching), label 0 is a special label known as the Implicit Null Label.

If an LSR (Label Switching Router) finds that the label to be swapped is 0, it performs PHP (Penultimate Hop Popping), meaning:✅ The label is removed (popped) from the MPLS packet.✅ The IP packet is forwarded to the next hop without an MPLS label.✅ This optimization reduces label processing overhead at the egress router.

???? Reference: HCIP-Datacom Advanced Routing & Switching Technology – MPLS Label Processing & PHP Mechanism

Comprehensive and Detailed In-Depth Explanation:

OSPFv3 (for IPv6) packets are directly encapsulated in IPv6 without using UDP or TCP.

The Next Header field in IPv6 is similar to the Protocol field in IPv4, indicating the protocol type of the payload.

IANA (Internet Assigned Numbers Authority) has assigned protocol number 89 to OSPF.

OSPFv3 packets always use Next Header value = 89 inside IPv6 headers.

???? Reference: HCIP-Datacom Advanced Routing & Switching Technology – OSPFv3 Packet Encapsulation

1. Understanding Router-LSAs in OSPFv3

Router-LSA (Type 1 LSA) is generated by every OSPFv3 router to describe its own links and connected networks within the same area.

Each router in an OSPF area generates exactly one Router-LSA to advertise its own topology information.

Router-LSAs are flooded throughout the area but do not cross area boundaries.

2. Analyzing the Given OSPFv3 Network

The topology consists of three routers: R1, R2, and R3, all connected in OSPFv3 Area 0.

Since all three routers participate in OSPFv3, each router generates its own Router-LSA (Type 1 LSA).

R2, as an OSPF router, will have its own Router-LSA and also receive the Router-LSAs from R1 and R3.

3. Counting the Number of Router-LSAs in R2’s LSDB

R1 generates 1 Router-LSA (for itself).

R2 generates 1 Router-LSA (for itself).

R3 generates 1 Router-LSA (for itself).

Total Router-LSAs in R2’s LSDB = 3 (one from each router).

Final Answer:

Answer: 3

HCIP-Datacom-Advanced Routing & Switching Technology References:

OSPFv3 LSA Types and Their Roles

Understanding Router-LSA (Type 1) and Its Function in LSDB

Comprehensive and Detailed In-Depth Explanation:

Understanding the IS-IS Levels and Default Route Advertisement:

R1 is a Level-1 router

R2 is a Level-1-2 router (meaning it connects both Level-1 and Level-2 areas)

R3 is a Level-2-only router

Step 1: What Does "default-route-advertise always level-1" Do?

This command forces R1 to advertise a default route (0.0.0.0/0) to all its Level-1 IS-IS neighbors, regardless of whether R1 has a default route in its routing table.

Since R1 is a Level-1 router, it does not participate in Level-2 routing, meaning it relies on R2 (a Level-1-2 router) for external connectivity.

Step 2: Checking the Routing Tables

R1: Since it is only a Level-1 router and does not receive a default route from any higher-level router, it does not have a default route in its own routing table. ✅ (D is correct)

R2: Since R1 advertises the default route at Level-1, R2 (a Level-1-2 router) receives this default route in its Level-1 database. ✅ (B is correct)

R3: R3 is a Level-2-only router, and default routes are not automatically leaked between Level-1 and Level-2 unless explicitly configured.

Since no explicit route leaking configuration is mentioned, R3 will not have the default route ❌ (C is incorrect).

A is incorrect because the command successfully advertises a default route from R1 to Level-1 neighbors like R2.

Final Answer: ✅ B, D

References:

HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – IS-IS Default Route Advertisement

IS-IS Routing Level-1 and Level-2 Behavior

IS-IS Route Leaking and Default Route Propagation