Free Huawei H12-891_V1.0 Practice Exam with Questions & Answers | Set: 2

Comprehensive and Detailed In-Depth Explanation:

The traceroute output shows that the path from R1 to the destination 172.17.1.5 is looping. After reaching the IP 10.1.13.1, the path goes back to 10.1.12.2, repeating the previous hops. This indicates a routing loop, where R1 continuously forwards packets through a circular path, never reaching the destination. Routing loops typically occur due to inconsistent or incorrect routing table entries, often because of routing protocol misconfigurations.

Understanding Inter-AS MPLS L3VPN Option C

???? MPLS L3VPN provides Layer 3 VPN services over an MPLS backbone by using BGP to exchange VPN routes.

???? Inter-AS MPLS L3VPN Option C (Carrier-to-Carrier Model) works as follows:

ASBRs (Autonomous System Boundary Routers) exchange VPNv4 routes using MP-BGP.

ASBRs do NOT store VPN routing tables. Instead, they advertise labeled IPv4 routes to enable inter-AS forwarding.

How ASBR-PE2 Enables Inter-AS Communication?

✅ VPNv4 Address Family (Answer A - Required)

Used to exchange MPLS VPN routes between PE routers.

MP-BGP (Multiprotocol BGP) exchanges VPNv4 prefixes between ASBR-PE1 and ASBR-PE2.

✅ Unicast BGP Address Family (Answer D - Required)

Required to exchange IPv4 labeled routes between ASBRs.

Ensures MPLS label forwarding between AS100 and AS200.

❌ BGP-LS Address Family (Answer B - Not Required)

BGP-LS (BGP Link-State) is used for SDN controllers to learn topology information.

It is not required for Inter-AS MPLS L3VPN.

❌ VPN Instance Unicast Address Family (Answer C - Not Required)

This is used for PE-CE communication but is not required between ASBRs.

Why is the Answer A, D?

✅ VPNv4 routes enable inter-AS VPN communication.

✅ IPv4 unicast routes are required for ASBR-PE2 to forward packets across AS boundaries.

Real-World Application:

Service Provider Networks: Used in carrier-to-carrier MPLS VPN deployments.

Enterprise WAN Interconnection: Enables multi-AS MPLS VPN connectivity for large enterprises.

✅ Reference: Huawei HCIE-Datacom Guide – Inter-AS MPLS L3VPN Option C (Carrier-to-Carrier Model)

This statement confuses congestion management with congestion avoidance:

Congestion Management: Refers to techniques like PQ, CQ, WRR, etc., to schedule packets in queues — i.e., manage how packets are sent, not discarded.

Congestion Avoidance: Techniques like WRED are used to preemptively discard packets to avoid full queues — these do discard packets.

Hence, congestion management does NOT discard packets — it ' s about controlling transmission order and prioritization.

Correct answer: B. FALSE

Understanding L3VPNv4 Over SRv6 BE

???? What is L3VPNv4?

L3VPNv4 (Layer 3 VPN over IPv4) allows MPLS-based VPN services over an SRv6 backbone.

Uses MP-BGP (Multiprotocol BGP) to distribute VPN routes.

???? Why is an RR (Route Reflector) Needed?

An RR simplifies BGP route exchange between multiple PEs (Provider Edge routers).

Without proper configuration, RRs may filter VPNv4 routes, preventing PEs from learning routes correctly.

Why is the Command peer retain-route-target all Needed?

✅ Ensures that the RR retains all VPNv4 routes.

✅ Prevents the RR from filtering route targets (RTs), allowing full VPN reachability.

✅ Without this command, the RR might not reflect all VPNv4 routes, causing connectivity issues.

Real-World Application:

Enterprise MPLS VPNs: Ensures correct BGP route reflection in an SRv6-based L3VPN.

Carrier Networks: Helps service providers maintain full BGP VPN route distribution.

✅ Reference: Huawei HCIE-Datacom Guide – BGP Route Reflectors in L3VPN over SRv6

Understanding VXLAN (Virtual eXtensible LAN) Technology

VXLAN is a Layer 2 over Layer 3 encapsulation protocol designed to extend Layer 2 domains across routed networks using MAC-in-UDP encapsulation.

???? Key VXLAN Components:

VTEP (VXLAN Tunnel Endpoints): These encapsulate and decapsulate VXLAN packets.

Underlay Network: The routed IP network that forwards VXLAN packets (does not require VXLAN awareness).

Overlay Network: The logical Layer 2 segments tunneled over VXLAN.

Analysis of the Answer Choices:

✅ A. VXLAN uses MAC-in-UDP encapsulation to encapsulate Ethernet packets into UDP packets and thereby extend Layer 2 networks.

Correct: VXLAN uses MAC-in-UDP encapsulation, meaning that the original Ethernet frame is placed inside a UDP packet, allowing Layer 2 networks to extend over IP-based networks.

❌ B. When VXLAN is deployed, in addition to devices at both ends of a VXLAN tunnel, intermediate forwarding devices are also required to support VXLAN. Otherwise, VXLAN packets cannot be forwarded.

Incorrect: VXLAN packets are forwarded as regular UDP traffic in the underlay network.

Intermediate routers or switches DO NOT need to support VXLAN, as they only forward UDP packets based on the outer IP headers.

Only VTEP devices must support VXLAN because they handle encapsulation/decapsulation.

✅ C. VXLAN packets are forwarded through routes on the underlay network, and the MAC address of the terminal in the inner data frame is not considered during underlay forwarding.

Correct: The underlay network routes VXLAN packets using outer IP headers (VTEP IP addresses), not the inner MAC address.

✅ D. VXLAN can be deployed on campus networks to implement Layer 2 and Layer 3 communication.

Correct: VXLAN is commonly used in campus networks to provide both Layer 2 bridging and Layer 3 routing across different locations.

Real-World Application:

Data Center Networks: VXLAN is widely used for multi-tenant network segmentation in cloud environments.

Enterprise Campus Networks: Enables seamless Layer 2 and Layer 3 connectivity across different buildings or locations.

✅ Reference: Huawei HCIE-Datacom Guide – VXLAN Deployment and Forwarding Principles

In BGP/MPLS IP VPN, when OSPF is used as the PE-CE routing protocol, Domain IDs are used to determine whether the OSPF routes imported into the VPN instance belong to the same OSPF domain.

How Domain ID Works in OSPF and MPLS VPN:

Same Domain ID (OSPF Intra-domain routes)

If the PE router ' s Domain ID matches the OSPF Domain ID, routes are treated as intra-area routes.

The routes retain OSPF attributes when redistributed into the VPN.

Different Domain ID (OSPF Inter-domain routes)

If the Domain ID does not match, routes are treated as external routes (Type 3 or Type 5 LSAs).

The PE router redistributes these routes as OSPF external routes.

Example Huawei Configuration for Domain ID in OSPF VPN:

ospf 1 vpn-instance VPN1

domain-id 1.1.1.1

This ensures consistent OSPF route types when exchanging routes between PE and CE.

Reference from Huawei HCIE-Datacom Documentation:

Huawei MPLS VPN Configuration Guide – OSPF Domain ID in PE-CE Routing

HCIE-Datacom Study Material – OSPF & MPLS VPN Route Redistribution

SRv6 Policies can be:

Statically configured via CLI on routers.

Dynamically generated and delivered from a controller such as Huawei iMaster NCE for centralized path computation.

This dual approach allows flexibility in deployments.

Exact Extract – Huawei SRv6 Deployment Guide:

“SRv6 Policies can be locally configured or dynamically delivered via PCEP from the controller, enabling both static and SDN-based implementations.”

Understanding SRv6 (Segment Routing over IPv6) Policies

???? What is an SRv6 Policy?

A traffic engineering (TE) mechanism used in SRv6-enabled networks.

Defines a set of Segment Routing (SR) paths that direct packets through a predefined set of waypoints.

Uses SRv6 SIDs (Segment Identifiers) instead of MPLS labels.

???? How Can SRv6 Policies Be Configured?

✅ Static SRv6 Policy Configuration:

Manually configured by network administrators.

Used in predictable, fixed network paths.

✅ Dynamic SRv6 Policy Generation:

Created dynamically by an SDN controller (e.g., Huawei iMaster NCE).

The controller analyzes network conditions and adjusts paths automatically based on traffic load and link failures.

Why is the Answer TRUE?

✅ SRv6 policies can be configured manually or dynamically delivered by a controller.

✅ SDN-based SRv6 solutions improve network automation and traffic engineering efficiency.

Real-World Application:

Cloud Data Centers: Uses dynamic SRv6 policies for optimal traffic distribution.

5G Transport Networks: Uses SRv6 TE for low-latency service guarantees.

✅ Reference: Huawei HCIE-Datacom Guide – SRv6 Policy and SDN Integration

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.