Huawei H12-891_V1.0 - HCIE-Datacom V1.0

For OSPF neighbors to reach Full state, they must exchange LSAs (Link State Advertisements) properly and synchronize their databases.

Possible Causes Preventing OSPF from Entering Full State:

✅ A. A link works abnormally

If the physical or Layer 2 link is unstable, OSPF Hello packets may be lost, preventing the Full state.

✅ B. The OSPF network types on both ends of the link are inconsistent

OSPF network types (Broadcast, P2P, NBMA, etc.) must match on both ends.

Example: If one router is P2P and the other is Broadcast, adjacency issues occur.

✅ C. The router IDs of neighbors are the same

Router ID conflicts prevent OSPF adjacencies from forming.

Each router must have a unique Router ID.

✅ D. The OSPF MTU values of interfaces on both ends of the link are different

If MTU settings do not match, OSPF Database Description (DD) packets may be dropped, preventing Full state.

Reference from Huawei HCIE-Datacom Documentation:

Huawei OSPF Configuration Guide – Troubleshooting OSPF Neighbor Issues

HCIE-Datacom Study Material – OSPF Adjacency and Route Synchronization

Comprehensive and Detailed Explanation:

R2 is an Area Border Router (ABR), meaning it connects multiple OSPF areas (Area 0 and Area 1).

ABRs generate Router-LSAs for each area they belong to.

Since R2 is part of both Area 0 and Area 1, it must generate Router-LSAs (Type 1) for both areas.

R2 does not forward Router-LSAs between areas; instead, it generates Summary LSAs (Type 3) to exchange routing information between areas.

Thus, the correct answer is D.

📖 Reference: Huawei HCIE Datacom – OSPF LSA Types and ABR Behavior

Comprehensive and Detailed Explanation:

Inter-AS MPLS L3VPN Option B requires ASBRs to exchange VPNv4 routes using eBGP with label information.

Analysis of Inter-AS VPN Solutions:

Option B uses eBGP to exchange labeled VPNv4 routes between ASBRs but does not require MPLS between ASBRs.

Option A does not exchange VPNv4 routes over ASBRs (uses IP routing instead).

Option C uses MP-BGP and requires full MPLS between ASBRs.

Since Option B requires ASBRs to exchange VPNv4 routes, the correct answer is B.

📖 Reference: Huawei HCIE Datacom – MPLS Inter-AS VPNs

Understanding the Network Scenario:

R2 is the boundary router between OSPF and IS-IS.

OSPF and IS-IS do not automatically redistribute routes between each other.

R4 ' s loopback (10.1.4.4/32) exists in the IS-IS domain.

To allow R1 (OSPF) to reach R4’s loopback, R2 must redistribute IS-IS routes into OSPF.

Why Option C Is Correct (✅)

✔ default-route-advertise in OSPF on R2:

This advertises a default route into the OSPF domain, allowing OSPF routers (R1, R3) to forward unknown traffic to R2.

Since IS-IS routes are not automatically injected into OSPF, this ensures R1 can reach R4.

✔ IS-IS Already Has Routes to OSPF

IS-IS routers (R3, R4) already learn routes from OSPF via R2 (assuming route redistribution is properly configured).

No need to run default-route-advertise in IS-IS.

Why Other Options Are Incorrect (❌)

❌ A. Run default-route-advertise in both OSPF and IS-IS views on R2

Unnecessary in IS-IS. The IS-IS domain already learns OSPF routes from R2 via redistribution.

Only OSPF needs a default route to forward unknown traffic to R2.

❌ B. No configuration is required

Incorrect, because OSPF does not automatically learn IS-IS routes.

A default route or redistribution is needed for R1 to reach R4.

❌ D. Run default-route-advertise only in the IS-IS view on R2

Incorrect, because IS-IS already has routing information from OSPF.

The issue is with OSPF not learning IS-IS routes, so the command needs to be in OSPF view.

📖 Reference: Huawei HCIE Datacom – OSPF and IS-IS Route Redistribution and Interoperability

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

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.

Understanding Inter-AS MPLS VPN Option C (Solution 2)

In MPLS L3VPN Inter-AS Option C, the Route Reflectors (RRs) are used for VPN route distribution but do not participate in data forwarding. The traffic forwarding path is based on MPLS labels assigned at different routers.

Each data packet carries two MPLS labels:

Transport Label (T1) – Used for forwarding within the backbone.

VPN Label (V1) – Used for VPN route identification.

Breaking Down the Labels:

✔ VPN Label (V1) – Allocated by PE1 (Answer: C ✅)

V1 (Inner Label) is the VPN label assigned by the egress PE router (PE1).

This label ensures that when the packet reaches PE1, it knows how to forward the traffic to CE1 (192.168.1.1).

✔ Transport Label (T1) – Allocated by P2 (Answer: B ✅)

T1 (Outer Label) is the transport label assigned by P2 to forward the packet across the AS core.

This label ensures the packet reaches the next-hop router (ASBR-PE1 in AS100).

Why Are the Other Options Incorrect?

❌ A. " T1 is allocated by RR2 " (Incorrect)

RR2 is used only for route reflection; it does not participate in label allocation or forwarding.

❌ D. " V1 is allocated by P2 " (Incorrect)

P2 is an intermediate router and does not allocate VPN labels.

VPN labels are always assigned by the egress PE router (PE1 in AS100).

📖 Reference: Huawei HCIE Datacom – MPLS L3VPN Inter-AS Option C

Comprehensive and Detailed In-Depth Explanation:

1. Understanding VXLAN Asymmetric IRB Forwarding:

In VXLAN (Virtual Extensible LAN) networks, there are two types of IRB forwarding: Symmetric IRB and Asymmetric IRB.

In Asymmetric IRB, routing occurs only at the ingress VTEP (Virtual Tunnel Endpoint).

The ingress VTEP (VTEP1) encapsulates the original data frame and sends it to the egress VTEP (VTEP2) over the VXLAN tunnel.

The destination MAC address of the original Ethernet frame is the MAC address of the Layer 3 gateway (VBDIF) at the egress VTEP.

2. Analyzing the Topology:

PC1 (172.16.2.1/24) with MAC A is sending traffic to PC2 (172.16.1.2/24) with MAC D.

Both PCs are in different subnets, so inter-subnet routing is required.

VTEP1 (1.1.1.1) on SW1 is the ingress VTEP.

VTEP2 (2.2.2.2) on SW2 is the egress VTEP.

The VXLAN Network Identifier (VNI) for the traffic is 100.

SW1 has two VBDIF interfaces:

VBDIF10 (MAC B) - Interface for BD10 (172.16.2.254).

VBDIF20 (MAC C) - Interface for BD20 (172.16.1.254).

3. Packet Flow in Asymmetric IRB:

Step 1: PC1 sends a packet destined for PC2. The packet is routed at the ingress VTEP (SW1) using the VBDIF interface (VBDIF10 with MAC B).

Step 2: The ingress VTEP (SW1) encapsulates the packet in a VXLAN header (VNI 100) and sends it to VTEP2.

Step 3: The original data frame inside the VXLAN packet must have a destination MAC address that matches the gateway MAC address (VBDIF20 - MAC C) at the egress VTEP (SW2).

Step 4: On reaching VTEP2, the encapsulation is removed, and the original frame with destination MAC C is forwarded.

Step 5: VTEP2 performs Layer 3 routing to forward the packet to PC2.

4. Why MAC C is Correct:

In asymmetric IRB forwarding, the routing decision at the ingress VTEP ensures that the destination MAC in the original frame is set to the VBDIF (gateway) MAC of the egress VTEP.

Since the egress VTEP (SW2) has VBDIF20 (MAC C) for the destination subnet (172.16.1.0/24), the destination MAC address of the original frame is MAC C.

From the output:

Tunnel destination IP address: Clearly shown as destination 10.0.1.1 → ✅

Tunnel interface MTU: Shown as The Maximum Transmit Unit is 1500 → ✅

Tunnel interface IP: Shown as Internet Address is 20.1.1.2/24 → ✅

Tunnel source: Tunnel source 10.0.3.3 (LoopBack0) → Not 10.0.1.1 → ❌

Therefore:

A — Correct

B — Correct

C — Correct

D — Incorrect (confuses destination as source)

Correct answers: A, B, C