Pass the Huawei HCIE-Datacom H12-891_V1.0 Questions and answers with ExamsMirror

Let’s analyze the scenario and each statement carefully based on OSPF path selection and BGP behavior in Huawei routers.

✅ Option A: The preferred path is R1–R3–R4.

According to the OSPF cost values:

R1–R3–R4: Cost = 1 + 1 = 2

R1–R2–R4: Cost = 2 + 2 = 4

OSPF chooses the lowest-cost path to reach a destination. Therefore, R1 will prefer the R1–R3–R4 path to reach 172.20.1.4/32.

Huawei Datacom Reference:

" OSPF selects routes based on the shortest path calculated using link costs. The router always selects the path with the lowest cost. "

(Source: HCIE-Datacom Study Guide v3.0 – OSPF Path Selection, Chapter 5)

✅ Option B: If the stub router on-startup command is run on R3, packet loss occurs during the power-off process of R3 but no packet loss occurs during the startup process of R3.

When R3 is powered off, OSPF needs to reconverge, which causes temporary packet loss.

When R3 starts up, it will advertise itself as a stub router using the stub-router on-startup command. This tells OSPF not to use R3 as a transit path during the startup period, thus preventing traffic blackholing.

Huawei Datacom Reference:

" stub-router on-startup command prevents a newly started router from being used as a transit node by OSPF, allowing routing to remain stable during convergence. "

(Source: HCIE-Datacom Study Guide v3.0 – OSPF Stub Router Functionality, Chapter 6.2)

❌ Option C: The preferred path is R1–R2–R4.

This is incorrect because the OSPF path cost via R2 is higher (4) than the cost via R3 (2).

❌ Option D: Packet loss occurs during both the power-off and startup processes of R3.

Incorrect. As explained above, when the stub-router on-startup command is used, packet loss is avoided during startup, but still occurs during power-off since the alternate path requires convergence.

Comprehensive and Detailed In-Depth Explanation:

In BGP EVPN, Type 2 routes (MAC/IP Advertisement routes) are used to advertise:

MAC addresses of endpoints.

ARP entries (MAC-to-IP bindings).

IRB (Integrated Routing and Bridging) routes, allowing the advertisement of both Layer 2 and Layer 3 reachability.

These routes are essential for enabling dynamic VXLAN tunnel establishment and seamless host mobility.

Type 1 (Ethernet Auto-Discovery): Used for multi-homing information.

Type 3 (Inclusive Multicast Ethernet Tag): Used for BUM (Broadcast, Unknown unicast, and Multicast) traffic.

Type 4 (Ethernet Segment): Used for identifying Ethernet segments in multi-homing scenarios.

Understanding the Command Components:

This is a Huawei CLI command used for diagnosing connectivity within a VPN instance in an MPLS network.

ping -aX → Specifies the source IP address (X) of the ping packets.

-cY → Specifies the number of ICMP Echo Request packets to send (Y).

-sZ → Defines the size (in bytes) of each ICMP Echo Request packet (Z).

-vpn-instance M → Specifies the VPN instance (VRF) M to which the ping packets belong.

Why are all options correct?

✅ A. The source IP address of the ping packets is X.

The -aX option forces the ping to originate from IP X instead of the default interface IP.

✅ B. The ping packets belong to VPN instance M.

The -vpn-instance M option ensures the ping is sent within VPN instance M, allowing verification of MPLS L3VPN routing.

✅ C. During the ping operation, the quantity of ICMP Request packets is Y.

The -cY parameter sets the number of ICMP Echo Requests to be sent, making Y the total count.

✅ D. The size of each ICMP Request packet for the ping operation is Z bytes.

The -sZ parameter defines packet size, helping to test MTU (Maximum Transmission Unit) issues.

Real-World Application:

Verifying MPLS VPN connectivity: Ensure customer networks are reachable within separate VRFs.

Testing MTU & fragmentation: Using -sZ, operators can check if packet fragmentation occurs.

Debugging asymmetric routing issues: By forcing -aX, engineers can trace return paths.

✅ Reference: Huawei HCIE-Datacom Official Guide – MPLS VPN Troubleshooting & Ping Options

Comprehensive and Detailed In-Depth Explanation:

In large- and medium-sized campus networks, Multi-mode authentication is commonly used for PCs connected to IP phones. This is because multi-mode authentication allows:

Multiple authentication methods on the same interface, such as MAC address authentication for the IP phone and 802.1X authentication for the PC.

This setup is ideal for scenarios where both devices share a single network port but require different authentication mechanisms.

MAC address authentication (A) and 802.1X authentication (B) individually cannot accommodate both devices efficiently.

Portal authentication (D) is mainly used for guest access and is not practical for IP phone and PC connections.

The Differentiated Services (DiffServ) model for Quality of Service (QoS) enables traffic management based on predefined priorities. This involves classifying, policing, queuing, and scheduling traffic to ensure efficient network resource utilization.

Breakdown of Each QoS Processing Step:

✅ Step 1: Traffic Classification and Marking

Purpose: Identifies and marks packets based on QoS attributes such as DSCP (Differentiated Services Code Point) or 802.1p priority bits.

Function: Assigns a QoS label to packets for further processing.

Example: Packets carrying voice traffic (EF - Expedited Forwarding) are marked for high-priority treatment.

✅ Step 2: Traffic Policing (CAR - Committed Access Rate)

Purpose: Enforces bandwidth limits on specific traffic flows to prevent excessive usage.

Function: Drops or re-marks packets exceeding the assigned bandwidth threshold.

Example: If a video stream exceeds 10 Mbps, excess packets may be dropped or re-marked.

✅ Step 3: Congestion Management (Queuing and Scheduling)

Purpose: Manages traffic flow through queues based on assigned QoS levels.

Function: Places packets in appropriate priority queues (e.g., Strict Priority, Weighted Fair Queuing - WFQ, CBWFQ).

Example: Voice packets are assigned to high-priority queues for low-latency forwarding.

✅ Step 4: Congestion Avoidance

Purpose: Prevents network buffer overflows and excessive packet drops.

Function: Uses mechanisms like WRED (Weighted Random Early Detection) to drop lower-priority packets before congestion occurs.

Example: If a queue reaches 80% capacity, WRED may drop low-priority packets to maintain QoS.

✅ Step 5: Traffic Shaping

Purpose: Smooths out traffic bursts to maintain a consistent transmission rate.

Function: Buffers and delays packets to prevent excessive packet drops.

Example: If outgoing traffic exceeds 50 Mbps, shaping ensures it does not exceed this limit while maintaining steady flow.

Comprehensive and Detailed In-Depth Explanation:

MACsec (Media Access Control Security) is a security protocol that provides secure communication over Ethernet links. It operates at the MAC layer (Layer 2) and offers the following key security services:

Integrity Check (B): Ensures that data has not been tampered with during transmission.

User Data Encryption (C): Protects data confidentiality by encrypting the payload.

Data Source Authenticity Verification (D): Confirms that the data originates from a legitimate source by using security associations.

Controllability Check (A) is not a service provided by MACsec. The term " controllability " typically relates to network management and configuration control rather than data security. MACsec primarily focuses on protecting data integrity, confidentiality, and authenticity, rather than controlling network elements or configurations.

In Huawei ' s SD-WAN architecture, the following channels are defined:

Management Channel (Callout 1)

Between iMaster NCE and Edge devices.

Used for device registration, configuration, and monitoring.

Encrypted with HTTPS.

Control Channel (Callout 2)

Between Edge devices and RR (Route Reflector).

Used for route exchange and control signaling, typically over MPLS or Internet.

Data Channel (Callout 3)

Between Edge to Edge (e.g., HQ to branch).

Used for actual service traffic transmission, carried over MPLS, Internet, or both.

Correct Mapping:

Management channel → Callout 1 (from iMaster NCE to Edge)

Control channel → Callout 2 (Edge to RR)

Data channel → Callout 3 (Edge to Edge, over MPLS/Internet)

Comprehensive and Detailed In-Depth Explanation:

When invoking RESTful APIs in iMaster NCE-Campus, the client must include the ACCESS-TOKEN in the request header to authenticate the request.

The ACCESS-TOKEN is obtained through authentication and is required for API access control.

The correct format in the HTTP header is:

Authorization: Bearer ACCESS-TOKEN

Other formats like ACCEPT-TOKEN, X-ACCEPT-TOKEN, and X ACCESS TOKEN are not recognized or valid for iMaster NCE-Campus API requests.

Therefore, the correct answer is A.

Comprehensive and Detailed In-Depth Explanation:

In the Huawei iMaster NCE-Campus solution, when using a third-party Portal authentication application, the following process occurs:

After the Wi-Fi user connects to the network, any attempt to access a website for the first time triggers HTTP redirection.

The user is redirected to the login page provided by the third-party authentication application.

This mechanism ensures that the user authenticates before accessing external resources.

The redirection behavior is consistent with captive portal functionality, which is standard for user authentication on Wi-Fi networks.

Therefore, the statement is TRUE.

Portal Authentication vs. MAC Authentication

✅ Portal Authentication

Used in high-mobility environments (e.g., shopping malls, hotels, and public Wi-Fi hotspots).

Users authenticate via a web portal before gaining network access.

Supports multiple device types (smartphones, laptops, tablets, etc.).

✅ MAC Address Authentication

Used for dumb devices that cannot perform interactive authentication (e.g., printers, IP phones, cameras).

The network authenticates devices based on their MAC addresses automatically.

Often used in enterprise LANs to ensure unattended devices get network access securely.

Reference from Huawei HCIE-Datacom Documentation:

Huawei CloudCampus Authentication Guide – Portal and MAC Authentication

HCIE-Datacom Training Material – Access Control Mechanisms