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

Understanding User Authentication Points in a Network

Authentication points can be deployed at different network layers based on security and scalability needs:

✅ Access Layer Authentication:

Ensures high security & granular control (user-level authentication).

Preferred in high-security enterprise networks.

✅ Aggregation or Core Layer Authentication:

Reduces authentication overhead but provides less granular control.

Suitable for large-scale networks where authentication load needs to be balanced.

Analysis of the Answer Choices:

✅ A. Deploying user authentication points at the access layer achieves granular permission management and high network security.

Correct: Provides fine-grained control per user and prevents unauthorized access.

✅ B. Moving user authentication points from the access layer to the aggregation or core layer greatly reduces the number of user authentication points, thereby effectively mitigating the pressure on the AAA server.

Correct: Fewer authentication points mean less load on the AAA server.

✅ C. Deploying user authentication points at the access layer has both advantages and disadvantages when compared to doing so at the aggregation or core layer. Policy association can be applied if user authentication points are deployed at the access layer.

Correct: Policy-based authentication is best applied at the access layer for granular control.

❌ D. When user authentication points are moved from the access layer to the aggregation layer, MAC address authentication for users may fail.

Incorrect: MAC authentication works at both layers, but policy adjustments may be needed.

✅ Reference: Huawei HCIE-Datacom Guide – User Authentication Strategies in Enterprise Networks

Huawei iMaster NCE-Campus Wi-Fi Location-Based Services (LBS) use HTTP/HTTPS to send location data (such as AP association, signal strength, timestamp, etc.) to an external LBS platform.

The standard format for such data exchange is JSON (JavaScript Object Notation).

JSON is lightweight, readable, and widely supported by modern web APIs and platforms.

Other options:

XML: Used in legacy systems, heavier format.

HTML: Used for page rendering, not data transfer.

YAML: Used mainly in configurations, not standard for HTTP APIs.

Correct answer: C. JSON

The default port for iMaster NCE-Campus northbound RESTful APIs is 18006. This port is used by external platforms and applications to interact with iMaster NCE via its open API interface.

Exact Extract - Huawei iMaster NCE-Campus API Integration Guide:

“Northbound interfaces of iMaster NCE-Campus are accessible via port 18006 by default. This allows external systems to use open APIs for automation and integration.”

BGP EVPN Type 2 Route (MAC/IP Advertisement Route)

This route carries MAC and IP address bindings to inform remote VTEPs about locally learned endpoints.

Why Use arp collect host enable?

Collects ARP entries of locally connected hosts.

Enables BGP EVPN Type 2 route generation to distribute the learned ARP information.

Incorrect Answer Explanations:❌ A. mac-address xxxx-xxxx-xxxx – Manually configures a MAC address but does not enable ARP collection for EVPN Type 2 routes.❌ B. arp-proxy enable – Enables ARP Proxy but does not advertise ARP information using BGP EVPN.❌ D. arp distribute-gateway enable – Used in Distributed Anycast Gateway (DAG) mode but not for collecting host ARP data.

Reference from Huawei HCIE-Datacom Documentation:

Huawei VXLAN EVPN Configuration Guide – ARP Handling and EVPN Type 2 Routes

HCIE-Datacom Training Material – VTEP ARP Advertisement in VXLAN Networks

IS-IS (Intermediate System to Intermediate System) protocol has a limit on the size of Link-State PDUs (LSPs).

Why Fragmentation?

LSPs contain routing and topology information.

If the LSP exceeds the maximum size, fragmentation allows the device to store and forward more routes by breaking them into smaller LSPs.

Key Point: IS-IS fragmentation is essential in large-scale networks where routing tables grow beyond the default LSP size limit.

✅ Reference: Huawei HCIE-Datacom Guide - IS-IS Protocol and Route Scaling

Understanding MPLS Label Retention Modes

In MPLS (Multiprotocol Label Switching), a Label Switching Router (LSR) can operate in one of two label retention modes:

1️⃣ Liberal Label Retention Mode (LLRM)

Stores all labels received from neighbors, even if they are not immediately used.

Advantage: Fast convergence during link failures.

Disadvantage: Consumes more memory & label space.

2️⃣ Conservative Label Retention Mode (CLRM)

Only keeps labels for the best next-hop path.

Advantage: Saves memory & label space.

Disadvantage: Slower convergence when topology changes.

Why are C and D Correct?

✅ C. An LSR reserves all labels distributed by its neighbor.

Correct: In Liberal Mode, the router accepts and stores all labels received, even for non-best paths.

✅ D. The liberal mode requires more memory and label space.

Correct: Since the router keeps all labels, it requires higher memory & storage.

Why are A and B Incorrect?

❌ A. An LSR retains labels from a neighboring LSR only when the neighbor is its next hop.

Incorrect: This describes Conservative Mode, not Liberal Mode.

❌ B. This label retention mode saves memory and label space.

Incorrect: Liberal Mode consumes more memory, not less.

Real-World Application

Liberal Mode is used in large-scale MPLS networks where fast failover is critical.

Conservative Mode is preferred in memory-constrained environments.

✅ Reference: Huawei HCIE-Datacom Study Guide – MPLS Label Retention Modes

Let’s break this down step-by-step based on Huawei IS-IS VPN and multi-process behavior.

???? Configuration Summary:

Process 1: IS-IS for the global routing table

Process 2: IS-IS for VPN instance tt

Process 3: IS-IS for VPN instance rr

✅ Option C: Correct

Process 1 contains only global routing information.

The configuration of isis 1 does not include any vpn-instance keyword, meaning it is bound to the global routing table.

It does not interact with VPN routing tables unless explicitly configured with import/export mechanisms or route leaking (which is not shown here).

Huawei Datacom Reference:

“When an IS-IS process is not associated with a VPN instance, it belongs to the global routing table and only maintains global routes.”

(Source: HCIE-Datacom Study Guide v3.0 – Chapter: IS-IS for IPv4 and IPv6, Section: Multi-Instance Routing)

✅ Option D: Correct

Routing information of process 2 is isolated from that of process 3.

isis 2 is bound to VPN instance tt

isis 3 is bound to VPN instance rr

Each IS-IS process in Huawei VRF context maintains independent LSDBs and routing tables, and by default, they do not share routing information unless route leaking or redistribution is configured (which is not shown in the config).

Huawei Datacom Reference:

“IS-IS processes bound to different VPN instances operate independently and do not share routing information.”

(Source: HCIE-Datacom Study Guide v3.0 – Chapter: MPLS L3VPN with IS-IS)

Understanding User Isolation in the Same VLAN

In a traditional VLAN, all devices within the same VLAN can communicate unless additional security policies are applied. To isolate users within the same VLAN, the following technologies can be used:

✅ B. Port Isolation (Private VLAN or Layer 2 Isolation)

Prevents communication between ports within the same VLAN.

Common in enterprise and campus networks to improve security.

Example: Isolating guest users from employees within the same VLAN.

✅ C. IPSG (IP Source Guard)

Blocks IP address spoofing within the same VLAN.

Uses DHCP snooping binding table to verify whether a device is using an authorized IP address.

✅ D. Ethernet Port Security

Limits the number of MAC addresses allowed per port.

Prevents unauthorized devices from communicating within the VLAN.

❌ A. Super VLAN (Incorrect Choice)

Super VLAN groups multiple VLANs under a single Layer 3 gateway, but it does not provide isolation within the same VLAN.

Real-World Application:

Public Wi-Fi Networks: Ensures that users within the same VLAN cannot communicate with each other.

Enterprise Security: Prevents unauthorized access or attacks within shared VLANs.

✅ Reference: Huawei HCIE-Datacom Guide – VLAN Security and User Isolation Technologies

Comprehensive and Detailed In-Depth Explanation:

The diagram shows a WAN network where Segment Routing (SR) is used in conjunction with the iMaster NCE controller. The network consists of Data Centers (DCs), Branches, Provider Edge (PE) routers, and Route Reflectors (RR) within AS 65600. Let ' s analyze each network technology and its placement in the scenario.

1. BGP-LS (Border Gateway Protocol - Link State):

Application Location: 1 (PE to RR)

Explanation:

BGP-LS is used to collect and distribute network topology information from the IGP (Interior Gateway Protocol) domain.

It enables the iMaster NCE (controller) to learn about the network topology and SR information from PE routers.

The PE routers send their link-state information to the RR using BGP-LS.

Why Location 1:

The RR collects topology data from PEs and forwards it to the controller for path computation.

2. BGP (Border Gateway Protocol):

Application Location: 2 (RR to iMaster NCE)

Explanation:

Standard BGP is used for route distribution and network connectivity.

The RR uses BGP to exchange route information with the controller (iMaster NCE).

Why Location 2:

The RR aggregates routes and exchanges them with the iMaster NCE for centralized management.

3. MP-IBGP (Multiprotocol Internal BGP):

Application Location: 3 (PE to PE)

Explanation:

MP-IBGP is used to exchange VPNv4 and VPNv6 routes between PE routers within the same AS.

It allows PEs to advertise VPN routes across the backbone network.

Why Location 3:

PEs need to communicate VPN-related information within the AS, ensuring end-to-end connectivity between DCs and branches.

4. BGP SR-Policy/PCEP (Path Computation Element Protocol):

Application Location: 4 (iMaster NCE to PE)

Explanation:

BGP SR-Policy and PCEP are used by the controller to distribute SR policies to the PE routers.

The iMaster NCE calculates optimal paths and sends the SR policies to PEs via BGP SR-Policy or PCEP.

Why Location 4:

The controller programs the Segment Routing paths directly to the PEs for optimal traffic engineering.

Why This Mapping Is Correct:

The mapping is based on the roles and functions of each protocol within the SR-based WAN architecture. The controller uses BGP-LS to learn topology, BGP for route reflection, MP-IBGP for VPN route exchange, and BGP SR-Policy/PCEP for path computation and distribution.

Understanding MPLS LDP and PHP (Penultimate Hop Popping):

✔ Label Distribution in MPLS LDP:

LDP assigns labels to FECs so that routers can forward packets based on labels rather than IP lookup.

Labels are advertised downstream (from R4 to R3, R3 to R2, and so on).

✔ Penultimate Hop Popping (PHP) Concept:

The egress LSR (R4) does not require an incoming label for 4.4.4.0/24.

Instead, R3 (Penultimate LSR) removes the label before forwarding the packet to R4.

R3 forwards the packet as an IP packet, not an MPLS packet, to avoid an unnecessary label lookup at R4.

In MPLS LDP, the label " 0 " is used to indicate an implicit NULL label (PHP operation).

Why the Answer is " 0 " (Implicit NULL Label)?

✅ Since R4 is the egress LSR, it does not need a label for 4.4.4.0/24.

✅ R3 assigns the outgoing label as " 0 " (Implicit NULL Label) to indicate that the label should be removed before sending to R4.

✅ R4 receives the packet as a pure IP packet (no MPLS label).

Why Other Answers Are Incorrect?

❌ Any value other than " 0 "

If R3 assigns a label (e.g., 100), R4 would need to perform an unnecessary MPLS lookup, which is inefficient.

Using " 0 " ensures PHP occurs, optimizing the forwarding process.

Final Answer: 0

???? Reference: Huawei HCIE Datacom – MPLS LDP and Penultimate Hop Popping (PHP)