H12-891_V1.0 Questions and Answers

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

From the IS-IS error output, the key error is:

Mismatched Area Addr(L1): 13

This clearly indicates that the area addresses are different, which prevents the Level-1 adjacency from forming.

Why is Option D Correct?

IS-IS Level-1 routers must have the same area ID to form an adjacency.

Since the log shows a mismatched area address, the adjacency fails at Level-1.

If R3 and R4 were Level-2 routers, they could form an adjacency even with different area IDs.

Why Are the Other Options Incorrect?

❌ Option A: No authentication failure is reported.❌ Option B: No "Mismatched Level" errors appear, so their levels are compatible.❌ Option C: No "Bad Circuit Type" errors indicate mismatched circuit types.

Thus, the correct answer is D.

???? Reference: Huawei HCIE Datacom – IS-IS Neighbor Troubleshooting

Understanding SRLB (Segment Routing Local Block)

???? What is SRLB?

SRLB (Segment Routing Local Block) is a range of local MPLS labels used by Segment Routing (SR-MPLS).

These labels are only relevant to the local router and are not advertised to other routers.

???? Key SR-MPLS Label Blocks:✅ SRGB (Segment Routing Global Block) – Globally significant labels shared among routers.✅ SRLB (Segment Routing Local Block) – Locally significant labels, not shared.

Why is the Answer TRUE?

✅ SRLB labels are only locally defined and are NOT distributed via IGP (OSPF or IS-IS).✅ They are used for local forwarding decisions within an SR-enabled router.✅ Only SRGB labels are advertised to ensure consistent global label assignment.

Real-World Application:

Traffic Engineering (TE): Uses SRLB for custom local path optimizations.

Segment Routing Networks: Ensures scalable MPLS forwarding without requiring full LDP signaling.

✅ Reference: Huawei HCIE-Datacom Guide – Segment Routing Label Blocks (SRGB & SRLB)

Authentication Header (AH) in IPsec

The Authentication Header (AH) protocol is part of IPsec and provides authentication, integrity, and replay protection but does NOT provide encryption.

✅ B. AH provides data origin authentication.

Ensures that packets come from a trusted source using cryptographic signatures.

✅ C. AH provides anti-replay protection.

Uses sequence numbers to prevent attackers from replaying old packets.

✅ D. AH provides data integrity authentication.

Ensures data integrity by verifying that packets have not been tampered with during transmission.

❌ A. AH provides packet encryption – Incorrect!

AH does not encrypt packet contents. It only authenticates headers.

ESP (Encapsulating Security Payload) is used for encryption in IPsec.

Reference from Huawei HCIE-Datacom Documentation:

Huawei IPsec Configuration Guide – AH vs. ESP

HCIE-Datacom Training Material – IPsec Security Mechanisms

To determine R3’s role (Level-1, Level-2, or Level-1-2) based on the provided output of the display ipv6 routing-table protocol isis command on R3, we need to analyze the IS-IS routing information and understand IS-IS hierarchy and behavior, particularly in the context of IPv6 routing. Let’s break it down step by step:

Understanding the IS-IS Levels and Hierarchy:

IS-IS (Intermediate System to Intermediate System) is a link-state routing protocol that supports a two-level hierarchy:

Level-1: Routers within the same area, responsible for intra-area routing. Level-1 routers only maintain routing information for their area and rely on Level-1-2 routers to reach other areas.

Level-2: Routers that form the backbone, connecting different areas for inter-area routing. Level-2 routers maintain routing information across areas.

Level-1-2: Routers that operate both at Level-1 (within their area) and Level-2 (to connect to other areas). These routers act as boundary routers between Level-1 areas and the Level-2 backbone.

A router’s role (Level-1, Level-2, or Level-1-2) determines which types of adjacencies it can form and what routing information it advertises or receives.

Analyzing the Output:

The output shows R3’s IPv6 routing table with routes learned via IS-IS, specifically:

Destination: 2082:EDFC:DDCC::B824:0/127, Protocol: ISIS-L1

This route is learned via IS-IS Level-1 (ISIS-L1), indicating that R3 has a Level-1 adjacency and is receiving or advertising routes within its area.

The next hop (FE80::2E0:FCFF:FE45:6A3E) and interface (GigabitEthernet0/0/0) suggest this route is intra-area.

Destination: 2082:EDFC:DDCC::B891:0/127, Protocol: ISIS-L2

This route is learned via IS-IS Level-2 (ISIS-L2), indicating that R3 has a Level-2 adjacency and is receiving or advertising routes for inter-area or backbone routing.

The next hop (FE80::2E0:FCFF:FE50:406F) and interface (GigabitEthernet0/0/1) suggest this route is for a different area or the backbone.

Both Level-1 and Level-2 routes are present in R3’s routing table, which provides critical insight into R3’s role.

Determining R3’s Role:

Level-1 Routers:

Level-1 routers only participate in Level-1 adjacencies and maintain routing information for their area. They do not have Level-2 routes or adjacencies unless connected to a Level-1-2 router. Since R3 has a Level-2 route (ISIS-L2), it cannot be exclusively a Level-1 router.

Level-2 Routers:

Level-2 routers focus on inter-area routing and typically do not maintain Level-1 routes unless they are also configured as Level-1-2. Since R3 has a Level-1 route (ISIS-L1), it cannot be exclusively a Level-2 router.

Level-1-2 Routers:

Level-1-2 routers operate both at Level-1 (for intra-area routing) and Level-2 (for inter-area routing). They can form adjacencies with both Level-1 and Level-2 neighbors and maintain both types of routes. The presence of both ISIS-L1 and ISIS-L2 routes in R3’s routing table indicates that R3 is participating in both Level-1 and Level-2 adjacencies, making it a Level-1-2 router.

Evaluating Each Option:

A. R3 must be a Level-2 device.

This is incorrect because R3 has ISIS-L1 routes, indicating it is also participating in Level-1 adjacencies, which Level-2-only devices do not do. Level-2 devices focus solely on inter-area routing and do not maintain Level-1 routes.

B. The device role of R3 cannot be determined.

This is incorrect because the presence of both ISIS-L1 and ISIS-L2 routes in the routing table clearly indicates R3’s role. The combination of Level-1 and Level-2 routes confirms R3 is a Level-1-2 router.

C. R3 must be a Level-1-2 device.

This is correct. The routing table shows both ISIS-L1 (Level-1) and ISIS-L2 (Level-2) routes, meaning R3 is operating as both a Level-1 and Level-2 router, which defines a Level-1-2 device.

D. R3 must be a Level-1 device.

This is incorrect because R3 has ISIS-L2 routes, indicating it is also participating in Level-2 adjacencies, which Level-1-only devices do not do. Level-1 devices only maintain intra-area routes and rely on Level-1-2 routers for inter-area reachability.

Additional Considerations:

The Flags: D in the output typically indicates a directly connected route or a route downloaded to the forwarding table, but it does not affect the determination of R3’s IS-IS level.

The preference (15) and cost (20) are standard for IS-IS routes and do not impact the level determination.

In Huawei’s IS-IS implementation, routers can be configured explicitly as Level-1, Level-2, or Level-1-2 using commands like isis level-1-2 under the IS-IS process. The presence of both Level-1 and Level-2 routes confirms R3’s configuration as Level-1-2.

Huawei HCIE-Datacom Context:

According to Huawei HCIE-Datacom documentation, IS-IS routers can operate at different levels, and the routing table’s protocol type (ISIS-L1 or ISIS-L2) indicates the level of adjacency. A router with both Level-1 and Level-2 routes is necessarily a Level-1-2 device, as it participates in both intra-area and inter-area routing.

The display ipv6 routing-table protocol isis command on Huawei devices shows routes learned via IS-IS, and the protocol type (L1 or L2) directly reflects the router’s role in the IS-IS hierarchy.

Conclusion:

Based on the presence of both ISIS-L1 and ISIS-L2 routes in R3’s IPv6 routing table, R3 must be a Level-1-2 device, as it is participating in both Level-1 (intra-area) and Level-2 (inter-area) adjacencies. Therefore, the correct answer is C.

References to Huawei HCIE-Datacom Documents:

Huawei HCIE-Datacom V1.0 Training Material, Chapter on IS-IS Configuration and Hierarchy.

Huawei NE Series Router Configuration Guide, IS-IS Section (Level-1, Level-2, and Level-1-2 Operations).

Huawei Technical Whitepaper on IS-IS Protocol, discussing IPv6 Routing and Level Determination.

Before performing a network cutover (migration or upgrade), it is essential to collect baseline data to ensure that services operate normally before and after the change.

Importance of Pre-Cutover Information Collection:

Identifies Network Baseline – Helps compare pre-cutover and post-cutover performance.

Detects Hidden Issues – Ensures that no existing network issues interfere with the cutover process.

Prevents Service Interruptions – Ensures all dependent services are accounted for.

Provides Rollback Plan – If issues arise, administrators can restore previous configurations.

Reference from Huawei HCIE-Datacom Documentation:

Huawei Network Change Management Guide – Pre-Cutover & Post-Cutover Best Practices

HCIE-Datacom Training Material – Service Assurance & Risk Analysis

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.

Understanding HTTP Security Risks

???? What is HTTP?

HTTP (Hypertext Transfer Protocol) is a protocol used for communication between web clients (browsers) and servers.

It is unencrypted, making it vulnerable to security threats.

Potential Risks in HTTP Communication:

✅ A. Eavesdropping (Data Interception)

Correct: HTTP traffic is unencrypted, meaning attackers can capture data using tools like Wireshark or MITM (Man-in-the-Middle) attacks.

Example: Hackers intercept login credentials over public Wi-Fi.

✅ B. Pretending (Impersonation / Spoofing)

Correct: Without encryption or authentication, attackers can spoof legitimate websites.

Example: A phishing website mimics a banking login page to steal user credentials.

✅ C. Tampering (Data Manipulation)

Correct: Attackers can modify HTTP data in transit, changing the content sent to users.

Example: Injecting malicious scripts into a webpage (e.g., Cross-Site Scripting - XSS).

❌ D. Lost (Low Probability of Data Loss)

Incorrect: HTTP runs over TCP, which ensures reliable data transmission.

Packet loss is not a major security risk but rather a network performance issue.

How to Mitigate HTTP Risks?

Use HTTPS (HTTP Secure) → Encrypts data using TLS (Transport Layer Security).

Enable HSTS (HTTP Strict Transport Security) → Forces HTTPS connections.

Implement Web Application Firewalls (WAFs) → Protects against attacks like SQL Injection & XSS.

✅ Reference: Huawei HCIE-Datacom Guide – Network Security Risks in HTTP Communication

Understanding BGP Link State (BGP-LS)

???? What is BGP-LS?

BGP-LS (BGP Link-State) is an extension of BGP that allows routers to exchange network topology information via Link-State NLRI.

Helps SDN controllers and path computation elements (PCEs) make intelligent routing decisions.

???? What Does BGP-LS Advertise?✅ Node Information – Router IDs, Loopbacks✅ Link Information – Bandwidth, Delay, Cost✅ Prefix Information – Network Subnets✅ Topology Information – Full network graph

Why is the Answer TRUE?

✅ BGP-LS introduces a new NLRI format for advertising link-state information.✅ NLRI (Network Layer Reachability Information) is used to distribute topology data to SDN controllers.✅ It improves path optimization by enabling centralized traffic engineering decisions.

Real-World Application:

SDN-Based Traffic Engineering: Used in Segment Routing (SR) networks for centralized path selection.

MPLS TE (Traffic Engineering): Optimizes network paths dynamically based on real-time link-state data.

✅ Reference: Huawei HCIE-Datacom Guide – BGP Link-State (BGP-LS) Fundamentals

VXLAN Inter-Subnet Routing with Symmetric IRB

VXLAN supports inter-subnet routing using Integrated Routing and Bridging (IRB). In symmetric IRB, both ingress and egress VTEPs perform Layer 3 forwarding to ensure efficient packet forwarding across subnets.

✅ A. Both the ingress VTEP and egress VTEP forward packets based on the Layer 3 forwarding table.

In symmetric IRB, both ingress and egress VTEPs perform Layer 3 lookup and forwarding.

The ingress routes packets before encapsulating them in VXLAN, and the egress performs another Layer 3 lookup to determine final delivery.

✅ D. When VTEPs forward inter-subnet user communication packets, the VNI carried in the VXLAN header is the L3VNI.

L3VNI (Layer 3 VXLAN Network Identifier) is used for inter-subnet routing between VXLAN segments.

OSPFv3 (for IPv6) introduces significant changes compared to OSPFv2 (for IPv4).While both versions share similar routing mechanisms, there are key LSA format and functional differences beyond just address changes.

Major Differences Between OSPFv2 and OSPFv3:

Address Independence (LSA Format Changes)

OSPFv3 LSAs do not contain IP addresses directly; they rely on Link-LSA and Intra-Area Prefix LSA to advertise addresses.

In OSPFv2, IP addresses were included in LSA headers.

New LSA Types in OSPFv3

LSA Type 8 (Link-LSA): Advertises a router’s IPv6 address to neighbors.

LSA Type 9 (Intra-Area Prefix LSA): Replaces the address information in Router-LSAs and Network-LSAs.

Support for Multiple Address Families (AF)

OSPFv3 can support both IPv4 and IPv6 in newer implementations (RFC 5838).

Authentication Mechanism Removed

OSPFv3 relies on IPsec for authentication, whereas OSPFv2 had built-in authentication mechanisms.

Incorrect Statement Explanation:

❌ The statement "LSA formats and functions remain unchanged" is false because:

LSA structures were modified in OSPFv3.

New LSA types were introduced to handle IPv6 addresses separately.

Reference from Huawei HCIE-Datacom Documentation:

Huawei OSPFv3 Configuration Guide – LSA Differences from OSPFv2

HCIE-Datacom Study Material – OSPFv3 Evolution & IPv6 Implementation

Comprehensive and Detailed Explanation:

On-premise mode refers to deploying the Huawei iMaster NCE-Campus controller within the enterprise network instead of using a cloud-based solution.

✔ Best suited for small and midsize campus networks that require:

Greater control over data security

Local network automation

No reliance on cloud connectivity

Since on-premise mode is recommended for small and midsize campus networks, the statement is TRUE.

???? Reference: Huawei HCIE Datacom – iMaster NCE Deployment Modes

A screenshot of a computer AI-generated content may be incorrect.

IPsec (Internet Protocol Security) provides secure communication over IP networks by implementing multiple security functions.

✔ Data Origin Authentication:

Ensures that the sender of the data is genuine and not impersonated.

Uses techniques such as HMAC (Hash-Based Message Authentication Code).

Correct Match: "The receiver verifies the identity of the sender." ✅

✔ Data Encryption:

Protects data confidentiality by encrypting packets using AES, 3DES, or other encryption algorithms.

Ensures that only the intended recipient can decrypt the data.

Correct Match: "The sender encrypts the data, and the receiver decrypts the data." ✅

✔ Data Integrity:

Ensures that data is not altered in transit.

Uses cryptographic hashes (e.g., SHA-256) to verify integrity.

Correct Match: "The receiver verifies received data to determine whether the data has been tampered with." ✅

✔ Anti-Replay:

Protects against packet replay attacks, where an attacker resends captured packets to disrupt communication.

Uses sequence numbers to detect and reject duplicate packets.

Correct Match: "The receiver rejects duplicate data packets." ✅

???? Reference: Huawei HCIE Datacom – IPsec Security Functions

Comprehensive and Detailed Explanation:

✔ 802.1X authentication supports multiple logout mechanisms based on network conditions and security policies.

✔ Correct Logout Modes:✅ (A) Authentication Server Logout → The RADIUS server can terminate a session.✅ (B) Manual Logout → Users can disconnect manually.✅ (C) Access Device Logout → The switch/WLAN controller can enforce logouts (e.g., if inactivity is detected).

✔ Why Not (D)?❌ (D) Accounting Server Logout → The accounting server tracks session usage but does not enforce logouts.

???? Reference: Huawei HCIE Datacom – 802.1X Authentication & Session Termination

X = 0

Y = 0

Z = 1

Understanding MPLS Label Headers

???? What is MPLS (Multiprotocol Label Switching)?

MPLS is a high-performance forwarding technology that replaces IP lookups with label switching.

Packets are forwarded based on labels instead of destination IP addresses.

MPLS labels are stacked when passing through multiple hops.

???? MPLS Label Stack StructureEach MPLS label has four fields:

Label – 20-bit identifier used for forwarding.

EXP (Experimental Bits / Traffic Class) – 3-bit field used for QoS (Quality of Service).

S (Bottom of Stack) – 1-bit flag that indicates whether this is the last (bottom) label in the stack.

TTL (Time-To-Live) – 8-bit field to prevent loops.

Understanding the EXP Fields (X, Y, Z) in the Figure

The image shows a packet with three MPLS labels.

Each label has an EXP field (X, Y, Z) representing the QoS bits.

By default, MPLS EXP bits are copied from the top label to lower labels unless modified by QoS policies.

If no QoS policy modifies the EXP bits, they remain the default value of 0.

The bottom label in the stack (Label 3) often has an EXP value of 1 to indicate specific QoS policies.

Why Are the Answers X = 0, Y = 0, Z = 1?

✅ X = 0 (Default EXP for Label 1, the top label in the stack).✅ Y = 0 (EXP for Label 2, unchanged from the default value).✅ Z = 1 (EXP for Label 3, indicating a QoS setting applied to the bottom label).

Real-World Application:

MPLS QoS (Quality of Service): EXP values determine packet priority in Service Provider networks.

Traffic Engineering (TE): MPLS labels guide packets through optimized paths, ensuring low-latency services.

Enterprise WAN Optimization: MPLS traffic is prioritized for critical applications like VoIP, Video Conferencing, and Cloud Services.

✅ Reference: Huawei HCIE-Datacom Guide – MPLS Label Stack and QoS EXP Field Processing

Understanding IPsec SA (Security Association) Establishment

???? IPsec (IP Security) provides encrypted communication over IP networks.???? Security Associations (SAs) define encryption, authentication, and key parameters for IPsec tunnels.

Two IPsec SA Modes:

1️⃣ Manual Mode:

All parameters (keys, encryption methods, authentication settings) must be manually configured.

Keys do not change automatically, making it less secure.

2️⃣ IKE (Internet Key Exchange) Auto-Negotiation Mode:

Uses IKE Phase 1 and Phase 2 to automatically negotiate, generate, and exchange keys.

Keys are periodically refreshed, increasing security.

Uses Diffie-Hellman (DH) key exchange for secure key generation.

Why is Answer D Incorrect?

❌ D. SAs established in both manual and IKE auto-negotiation modes can be dynamically updated.

Incorrect: In manual mode, the IPsec SA is static and does not support dynamic updates.

Correct behavior: Only IKE auto-negotiation mode supports dynamic re-keying and SA updates.

✅ Reference: Huawei HCIE-Datacom Guide – IPsec SA Modes and IKE Negotiation

In the Huawei SD-WAN solution, LAN-side devices (such as CPEs and aggregation routers) use various routing protocols to connect to Layer 3 networks and exchange routes dynamically. The supported protocols include:

✅ A. IS-IS (Intermediate System to Intermediate System)

A link-state protocol often used in large enterprise networks for fast convergence and scalability.

✅ B. OSPF (Open Shortest Path First)

A widely used dynamic routing protocol for intra-domain (LAN) connectivity.

Commonly used in enterprise networks to connect SD-WAN edge routers to LAN networks.

✅ C. BGP (Border Gateway Protocol)

BGP is primarily used for WAN and internet connectivity, but it can also be used inside large enterprise networks for LAN-side routing.

BGP enables inter-domain routing and policy-based route control.

✅ D. RIP (Routing Information Protocol)

A legacy distance-vector protocol still supported in some networks for basic LAN routing.

Less preferred due to slow convergence and hop-count limitations.

Reference from Huawei HCIE-Datacom Documentation:

Huawei SD-WAN Deployment Guide – LAN-Side Routing Protocols

HCIE-Datacom Training Material – Routing Configuration in SD-WAN

Huawei SD-WAN supports various intelligent traffic steering mechanisms to optimize link utilization and balance network traffic across multiple links.

✅ D. Traffic bandwidth-based traffic steering

This method ensures that traffic is distributed across multiple links based on available bandwidth.

SD-WAN dynamically selects links based on their real-time bandwidth utilization, ensuring optimal performance and load balancing.

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

When Spanning Tree Protocol (STP) is not enabled on a network, loops can occur in Layer 2 Ethernet networks, leading to various network issues. STP is designed to prevent loops by blocking redundant paths, and its absence can cause broadcast storms, MAC address table instability, and resource exhaustion. Let’s analyze each option in the context of Huawei HCIE Datacom documentation and network behavior:

A. A loop alarm is generated on the LAN switch.

This option is incorrect. Huawei switches, as per HCIE Datacom standards, do not automatically generate a specific "loop alarm" unless configured with loop detection features (e.g., Huawei’s Loop Detection Protocol or similar mechanisms). Without STP or loop detection enabled, the switch may not explicitly generate an alarm for a loop; instead, it will exhibit symptoms like broadcast storms or flapping MAC entries. Therefore, this is not a direct symptom of an STP-less loop. Reference: Huawei HCIE Datacom V3.0 Training Materials, Section 4.2 – Spanning Tree Protocol and Loop Prevention.

B. CPU usage is too high.

This option is correct. When a loop occurs without STP, broadcast packets (and sometimes multicast or unknown unicast packets) circulate endlessly in the network. This leads to excessive processing by switches as they handle these packets, resulting in high CPU usage. Huawei switches, as described in HCIE Datacom documentation, can experience CPU overload due to continuous packet forwarding and processing in a looped environment. Reference: Huawei HCIE Datacom V3.0, Chapter 5 – Switch Performance and Loop Management.

C. MAC entries flap.

This option is correct. In a loop without STP, switches continuously receive frames from multiple ports, causing MAC address tables to update repeatedly as the same MAC address appears on different ports. This "flapping" of MAC entries destabilizes the network and can lead to incorrect frame forwarding. Huawei HCIE Datacom emphasizes MAC address table stability as a critical aspect affected by loops, as outlined in Section 4.3 – Ethernet Switching and Loop Mitigation. Reference: Huawei HCIE Datacom V3.0, Section 4.3.

D. Host receives a large number of broadcast packets.

This option is correct. A loop without STP causes broadcast packets to circulate indefinitely, creating a broadcast storm. Hosts connected to the network will receive an overwhelming number of these packets, potentially leading to performance degradation or even network timeouts. This is a well-documented symptom in Huawei HCIE Datacom training, specifically in discussions about loop prevention mechanisms. Reference: Huawei HCIE Datacom V3.0, Chapter 4 – Layer 2 Loop Prevention.

Thus, the correct symptoms of a loop occurring due to the absence of STP include high CPU usage, flapping MAC entries, and hosts receiving a large number of broadcast packets. Option A is incorrect as it requires specific loop detection configuration, which is not implied in the question.

References:

Huawei HCIE Datacom V3.0 Training Materials, Sections 4.2, 4.3, and 5 – Spanning Tree Protocol, Loop Prevention, and Switch Performance.

Huawei Official Documentation on Ethernet Switching and Loop Management, available in HCIE Datacom Certification Guides (2023 update).

Comprehensive and Detailed Explanation:

✔ Inter-VN communication allows users in different VNs (R&D and Marketing) to communicate.

✔ Correct Steps:✅ (B) Deploy a Policy Control Matrix → Defines rules for inter-VN communication between security groups.✅ (C) Configure Inter-VN Communication → Enables routing between VNs through the border gateway or firewall.

✔ Why Not Other Options?❌ (A) Deploy Network Service Resources → This is for internal VN service deployment, not inter-VN communication.❌ (D) Deploy an External Network → This is for Internet or WAN access, not internal VN-to-VN communication.

???? Reference: Huawei HCIE Datacom – Virtual Network Intercommunication

Comprehensive and Detailed Explanation:

✔ SRv6 (Segment Routing over IPv6) Flavors provide additional processing behaviors for SRv6 End instructions.

✔ PSP (Penultimate Segment Popping) Flavor:

PSP enables the penultimate node to remove the SRH (Segment Routing Header) before forwarding the packet to the last segment.

This reduces the processing overhead on the final segment node.

✔ Correct End Instructions for PSP:✅ (A) End.X → Cross-connect behavior between segments.✅ (C) End.T → Transport encapsulation in SRv6.✅ (D) End → Basic SRv6 endpoint behavior.

❌ (B) End.BM is incorrect → This is used for Binding Segment (BSID) behavior and does not support PSP.

???? Reference: Huawei HCIE Datacom – SRv6 Flavors and End Instructions

Understanding Huawei OPS and HTTP Communication

???? What is Huawei OPS?

Huawei Open Programmability System (OPS) enables API-based network automation using standard HTTP requests.

It supports NETCONF, RESTCONF, and RESTful APIs for device management.

???? Why TCP Port 80?

Port 80 is the default port for HTTP traffic.

Used for web-based device management, API calls, and telemetry data exchange.

If HTTPS (secure version) is used, the default port is 443.

Why is the Answer 80?

✅ HTTP operates on TCP port 80 by default.✅ Huawei OPS uses HTTP APIs to manage network devices, making port 80 the standard option.

Real-World Application:

Cloud-Native Network Automation: Uses HTTP-based APIs for SDN controllers and automation tools.

Network Device Management: Enables remote configuration and monitoring over HTTP APIs.

✅ Reference: Huawei HCIE-Datacom Guide – Open Programmability System (OPS) & HTTP Communication

Understanding Huawei SD-WAN VN (Virtual Network) Topologies

Huawei SD-WAN uses Virtual Networks (VNs) to provide traffic isolation and policy-based routing for different services, branches, and applications.

???? VN Topologies Can Be Different

Each VN (Virtual Network) can have its own topology.

Some VNs may use full-mesh, while others may use hub-and-spoke or star topology.

Different VNs can have different routing and security policies.

✅ Example:

Corporate traffic (VN1) → Full-mesh topology for efficient inter-branch communication.

Guest Wi-Fi traffic (VN2) → Hub-and-spoke topology to restrict inter-site communication.

Why is the Answer FALSE?

❌ All VNs do not have to use the same topology.✅ Each VN can be configured independently with a unique topology, routing policy, and security settings.

✅ Reference: Huawei HCIE-Datacom Guide – SD-WAN VN Topologies and Segmentation

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

Comprehensive and Detailed Explanation:

iMaster NCE-CampusInsight is Huawei's intelligent network analysis platform that:✔ Collects real-time telemetry data using SNMP, NetStream, and Telemetry.✔ Analyzes traffic patterns to detect network anomalies.✔ Uses AI-driven analytics to optimize network performance.

Thus, the statement is TRUE.

???? Reference: Huawei HCIE Datacom – iMaster NCE-CampusInsight Features

Understanding VGMP (Virtual Gateway Management Protocol)

???? What is VGMP?

VGMP (Virtual Gateway Management Protocol) is used in Huawei firewalls to manage hot standby (HRP - Hot Standby Routing Protocol).

Ensures that the active and standby firewalls synchronize their states for high availability.

???? How Does VGMP Work?

The Active and Standby firewalls exchange VGMP packets to maintain state synchronization.

These packets are encapsulated within UDP for transport.

The default UDP port for VGMP is 512.

Why is the Answer 512?

✅ Huawei firewalls use UDP port 512 by default for VGMP communication.✅ This ensures that VGMP heartbeats and synchronization messages are correctly processed.

Real-World Application:

Enterprise Firewalls: VGMP ensures failover between active and standby firewalls.

Carrier-Grade Firewalls: Uses VGMP with HRP to achieve zero-downtime firewall redundancy.

✅ Reference: Huawei HCIE-Datacom Guide – VGMP and HRP High Availability Mechanisms

BGP EVPN Route Types in VXLAN:

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

Used for host reachability advertisement.

Carries MAC and IP address information of endpoints.

Does not carry an IP Prefix field (Type 5 routes handle prefixes).

Correct Explanation of Answer Choices:✅ IP Address (B) is included – Used for host mobility and reachability.✅ L3VNI (C) is included – Used for Layer 3 VXLAN routing.✅ L2VNI (D) is included – Used for Layer 2 VXLAN bridging.❌ IP Prefix (A) is not included in Type 2 routes – It is part of EVPN Type 5 routes for prefix advertisement.

Reference from Huawei HCIE-Datacom Documentation:

Huawei VXLAN BGP EVPN Configuration Guide – Type 2 vs. Type 5 Routes

HCIE-Datacom Training Material – VXLAN Overlay Networks and BGP EVPN

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

Understanding VXLAN and ARP Suppression in BGP EVPN

VXLAN (Virtual Extensible LAN) is used to extend Layer 2 networks over Layer 3 infrastructure.

VXLAN uses VTEPs (VXLAN Tunnel Endpoints) to encapsulate and forward Layer 2 traffic.

BGP EVPN (Ethernet VPN) is used for MAC/IP address learning and distribution across VXLAN networks.

How ARP Request Forwarding Works in This Scenario?

1️⃣ ARP Broadcast Suppression Enabled (VXLAN Optimized Forwarding)

Since ARP broadcast suppression is enabled on VTEP1, the ARP request is not flooded.

Instead, VTEP1 checks its EVPN learned database to find PC2’s MAC address (MAC C).

2️⃣ VTEP1 Encapsulates the ARP Request

VTEP1 encapsulates the ARP request in a VXLAN packet and sends it to VTEP2.

The original ARP frame inside the VXLAN tunnel still has:

Source MAC: MAC A (PC1's MAC)

Destination MAC: MAC C (PC2's MAC, learned via EVPN)

3️⃣ VXLAN Outer Headers

The outer VXLAN header uses:

Source IP: 1.1.1.1 (VTEP1)

Destination IP: 2.2.2.2 (VTEP2)

VNI (VXLAN Network Identifier): 200 (BD 20)

4️⃣ VTEP2 Receives and Forwards the ARP Request

VTEP2 decapsulates the VXLAN packet and forwards the original ARP request to PC2 (MAC C).

This ensures that only the intended receiver (PC2) gets the ARP request, preventing unnecessary broadcast flooding.

Why the Answer is MAC C?

✅ B. MAC C is Correct

The destination MAC of the inner data frame is PC2’s MAC (MAC C).

This is because VTEP1 forwards the ARP request directly to VTEP2, which then forwards it to PC2.

Why Other Answers Are Incorrect?

❌ A. MAC B (Incorrect)

MAC B is VTEP1’s MAC address, which is used in the outer VXLAN header, not in the inner Ethernet frame.

❌ C. MAC A (Incorrect)

MAC A is the source MAC of the ARP request (PC1), not the destination.

❌ D. MAC D (Incorrect)

MAC D is not mentioned in the topology, so it is irrelevant.

???? Reference: Huawei HCIE Datacom – VXLAN BGP EVPN and ARP Suppression

Understanding VXLAN and BGP EVPN Control Plane

VXLAN (Virtual eXtensible LAN) is an overlay network technology that enables Layer 2 (L2) extension over an IP-based network using MAC-in-UDP encapsulation.

???? Traditional VXLAN Flooding Issue:

Without BGP EVPN, VXLAN uses flood-and-learn behavior for MAC address learning.

Broadcast, Unknown Unicast, and Multicast (BUM) traffic is flooded to all VTEPs, which is inefficient.

???? How Does BGP EVPN Solve Flooding?

BGP EVPN (Ethernet VPN) replaces the flood-and-learn model with a distributed control plane.

MAC/IP bindings are advertised through BGP EVPN Type 2 routes, eliminating the need for flooding ARP requests.

VXLAN routers learn MAC addresses proactively instead of relying on flooding.

Why is the Answer TRUE?

✅ BGP EVPN fully prevents ARP flooding by distributing MAC/IP bindings via control plane updates.✅ VTEPs only send traffic to known destinations, reducing network congestion.✅ BGP EVPN is the industry standard for large-scale data center and campus VXLAN deployments.

Real-World Application:

Data Centers: Avoids unnecessary ARP request flooding in large cloud networks.

Campus Networks: Reduces L2 broadcast storms, improving network efficiency.

Service Provider Networks: Enables scalable multi-tenant VXLAN solutions.

✅ Reference: Huawei HCIE-Datacom Guide – VXLAN BGP EVPN Control Plane Architecture

Comprehensive and Detailed Explanation:

✔ HTTP Status Code 401 Unauthorized indicates that authentication credentials were either:

Missing (e.g., no API key or token).

Invalid (e.g., expired session, incorrect credentials).

✔ Error Code Breakdown:✅ (D) "Unauthorized" (Correct) → Indicates the client must authenticate first.❌ (A) "Service Unavailable" (503) → Used when the server is down.❌ (B) "Access Denied" (403) → Used when the client lacks permission even after authentication.❌ (C) "Not Found" (404) → Used when the resource does not exist.

???? Reference: Huawei HCIE Datacom – iMaster NCE-Campus RESTful API Error Codes

Comprehensive and Detailed Explanation:

6PE (IPv6 Provider Edge) and 6VPE (IPv6 VPN Provider Edge) allow IPv6 traffic over an MPLS network, but they differ in VPN support and address isolation.

Comparison of 6PE vs. 6VPE:

A screenshot of a computer AI-generated content may be incorrect.

Since 6VPE supports VRFs, it allows IPv6 address reuse for different VPN customers.Thus, the correct answer is A.

???? Reference: Huawei HCIE Datacom – 6PE and 6VPE Implementation

Understanding OSPF Neighbor States

OSPF (Open Shortest Path First) establishes neighbor relationships through several states:

1️⃣ Down: No Hello packets received.2️⃣ Init: Router receives Hello packets but its own Router ID is missing in the received packets.3️⃣ 2-Way: Routers see each other in Hello packets. (Stable state for non-DR/non-BDR routers).4️⃣ ExStart: Routers start exchanging LSAs but may face MTU mismatches.5️⃣ Exchange: Routers send Database Description (DBD) packets to synchronize link-state databases.6️⃣ Loading: Routers exchange Link-State Requests (LSRs) & Updates (LSUs) to fully sync.7️⃣ Full: Routers are fully synchronized.

Analysis of the Answer Choices

✅ A. For non-DR and non-BDR routers on an Ethernet link, the 2-Way state is acceptable.

Correct: Non-DR/Non-BDR routers remain in 2-Way state since they don’t need to form full adjacency.

✅ B. The Init state indicates that the router has received Hello packets from its neighbors, but the received Hello packets do not contain the OSPF RID of the receiving router.

Correct: If an OSPF router receives a Hello but does not see its own Router ID, it stays in the Init state.

✅ C. The ExStart state indicates that two neighbor routers have inconsistent MTUs or the same OSPF Router ID (RID).

Correct: If MTUs mismatch or RIDs conflict, the DBD exchange fails, causing routers to remain in ExStart state.

❌ D. The Attempt state indicates that the router does not send unicast Hello packets to configured neighbors.

Incorrect:

In Attempt state, routers send unicast Hello packets to manually configured neighbors (common in NBMA networks).

If no Hello responses are received, they remain in Attempt state, but they DO send Hellos.

Real-World Application

OSPF Troubleshooting: Identifying routers stuck in Init or ExStart states can point to MTU mismatches or neighbor misconfigurations.

NBMA Networks (Frame Relay, DMVPN): Manually configured neighbors may stay in Attempt state if Hello packets are lost.

✅ Reference: Huawei HCIE-Datacom Study Guide – OSPF Neighbor States & Troubleshooting

Comprehensive and Detailed Explanation:

✔ Fit APs require additional configurations before going online, such as:

AP authentication and onboarding through DHCP Option 148 or manual registration.

Firmware upgrade and provisioning from iMaster NCE-Campus.

Policy enforcement and VLAN assignment.

Since additional steps are required, Fit APs do not go online immediately, making the statement FALSE.

???? Reference: Huawei HCIE Datacom – AP Registration and Authentication

Understanding screen-length Command in Huawei Devices

???? What Does screen-length Do?

Controls how much output is displayed at a time on the Huawei CLI.

By default, command output is paginated (split-screen display).

screen-length 0 temporary disables the split-screen display, allowing continuous output without pauses.

Analysis of Each Option:

❌ A. Performing automatic word wrap → Incorrect

This command does not wrap long text lines, it controls screen pagination.

❌ B. Performing split-screen display → Incorrect

This command disables split-screen display, not enables it.

✅ C. Canceling split-screen display → Correct

This allows continuous command output without "Press Enter to continue" interruptions.

❌ D. Canceling automatic word wrap → Incorrect

Word wrap behavior is not controlled by screen-length.

Real-World Application:

Automated Network Monitoring: Used in Python scripts for uninterrupted CLI output collection.

Log Analysis: Helps in extracting large command outputs for troubleshooting.

✅ Reference: Huawei HCIE-Datacom Guide – CLI Configuration and Automation with Paramiko

Comprehensive and Detailed Explanation:

✔ SRv6 (Segment Routing over IPv6) works by encoding a segment list in the IPv6 header.

✔ How SRv6 Works:

The Segments Left field indicates the remaining segments in the path.

Each endpoint node processes the next segment and decrements Segments Left by 1.

The IPv6 Destination Address (DA) is updated to the next segment.

Thus, the statement is TRUE.

???? Reference: Huawei HCIE Datacom – SRv6 Packet Forwarding

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 Performance Measurement in Huawei CloudWAN

Huawei CloudWAN enables intelligent traffic management, real-time network monitoring, and automated operations.

???? Traditional Performance Monitoring Methods

TWAMP (Two-Way Active Measurement Protocol) → Measures latency and jitter by injecting test traffic.

Telemetry → Provides real-time network visibility, but does not measure actual service traffic performance.

BGP FlowSpec → Used for DDoS mitigation, not performance measurement.

???? iFIT (In-situ Flow Information Telemetry)✅ iFIT is a next-generation performance monitoring technology that measures:

Real service traffic performance (latency, jitter, packet loss) in real time.

Packet forwarding behavior at each hop without injecting synthetic traffic.

Path delay and service degradation detection.

Why is Answer D Correct?

✅ iFIT provides real-time network performance monitoring based on actual service traffic.✅ Unlike TWAMP, iFIT does not require probe packets, reducing overhead.

Real-World Application:

5G Transport Networks: Ensures low-latency paths for ultra-reliable services.

CloudWAN Optimization: Detects network congestion without affecting user traffic.

✅ Reference: Huawei HCIE-Datacom Guide – iFIT and Intelligent Performance Monitoring

Understanding EVPN (Ethernet VPN) Label Allocation and ARP Handling

???? What Happens in This Scenario?1️⃣ CE1 (192.168.1.1) sends an ARP request to discover the MAC address of CE2 (192.168.1.2).2️⃣ PE1 receives the ARP request and needs to forward it over the EVPN fabric.3️⃣ To send the broadcast ARP request across the EVPN network, PE1 forwards the packet to PE4 using BUM (Broadcast, Unknown unicast, and Multicast) forwarding.4️⃣ PE4, as the Designated Forwarder (DF), forwards the ARP request to CE2.

Role of Labels in EVPN VXLAN/MPLS Networks

???? EVPN uses BGP to distribute MAC/IP reachability information using different route types.

✅ EVPN Type 2 Route (MAC/IP Advertisement Route):

Used for MAC-to-IP address mapping announcements.

Ensures remote VTEPs (PE routers) learn MAC-to-IP bindings dynamically.

✅ EVPN Type 3 Route (Inclusive Multicast Route):

Used for BUM traffic (Broadcast, Unknown Unicast, Multicast).

Assigns a multicast label (e.g., 201) to be used for forwarding broadcast packets like ARP requests.

???? In this case:

The label 201 is used for BUM traffic forwarding.

BUM traffic is handled using an EVPN Type 3 route.

Why is the Answer 3?

✅ EVPN Type 3 routes carry labels for BUM traffic, which includes ARP requests.✅ Label 201 is used for multicast distribution, which is managed by Type 3 routes.

Real-World Application:

VXLAN Data Centers: Uses EVPN Type 3 routes to control BUM traffic efficiently.

Campus Networks: Prevents unnecessary flooding of ARP requests across VXLAN domains.

✅ Reference: Huawei HCIE-Datacom Guide – EVPN BGP Route Types and Multicast Labeling

Comprehensive and Detailed Explanation:

Inter-AS MPLS L3VPN solutions enable communication between different Autonomous Systems (AS) while maintaining VPN separation. The three primary solutions for inter-AS MPLS L3VPN are:

Option A (Back-to-Back VRF)

MPLS is not required between ASBRs.

VPN routes are exchanged without label switching.

Each ASBR has a VRF instance configured and forwards traffic using plain IP routing.

Option B (eBGP Redistribution of Labeled VPNv4 Routes)

MPLS is not required between ASBRs.

ASBRs exchange labeled VPNv4 routes using eBGP.

The ASBR does not perform label switching but simply forwards packets based on VPNv4 labels.

Option C (Multi-Hop MP-BGP for VPNv4 Routes)

MPLS is required between ASBRs.

ASBRs establish label-switched paths (LSPs) to forward VPN traffic across AS boundaries.

Since Option B relies on labeled VPNv4 routes via eBGP and does not need MPLS between ASBRs, the correct answer is D.

???? Reference: Huawei HCIE Datacom Study Guide - MPLS VPN Inter-AS Solutions

Comprehensive and Detailed Explanation:

Ethernet VPN (EVPN) is an advanced L2VPN technology that enhances MAC learning and forwarding in data center and enterprise networks. Different EVPN route types are used for various functions:

Ethernet A-D (Auto-Discovery) Route: Used for auto-discovery of PE devices and does carry labels.

MAC/IP Advertisement Route: Distributes MAC-to-IP mappings and carries labels for forwarding decisions.

Ethernet Segment Route: Does not carry MPLS labels as it is used to signal multi-homing and redundancy information.

Inclusive Multicast Route: Used for multicast forwarding and carries labels for tunnel identification.

Since Ethernet Segment Route is used only for multi-homing signaling and does not carry MPLS labels, the correct answer is C.

???? Reference: Huawei HCIE Datacom Study Guide - EVPN Route Types

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)

Comprehensive and Detailed Explanation:

The IS-IS peer output shows:

IPv4 Peer Address: 10.1.34.1

IPv6 Peer Address: FE80::2E0:FCFF:FE98:2576

MT IDs (Multi-Topology) Supported: 0 (IPv4), 2 (IPv6)

Since both IPv4 and IPv6 peer addresses are listed, it confirms that both IPv4 and IPv6 IS-IS neighbor relationships are established between R4 and ee8c.a0c2.baf3.

???? Reference: Huawei HCIE Datacom – IS-IS Multi-Topology Support

Comprehensive and Detailed Explanation:

IP Source Guard (IPSG) is a Layer 3 security feature used to protect against IP address spoofing by filtering packets based on bound IP-MAC mappings.

Correct Statements:✔ IPSG is a Layer 3 filtering mechanism that checks if the source IP address of a packet matches the learned or configured bindings (Option B).✔ IPSG prevents unauthorized IP address changes by enforcing binding rules (Option C).✔ IPSG defends against IP spoofing attacks by dropping packets from unauthorized sources (Option D).

Incorrect Statement:❌ Option A is incorrect because IPSG does not send alarms to an NMS when an invalid packet is detected. Instead, it drops the packet.

Thus, the correct answer is A.

???? Reference: Huawei HCIE Datacom Security Guide - IP Source Guard (IPSG)

6PE (IPv6 Provider Edge over MPLS) vs. 6VPE (IPv6 VPN Provider Edge over MPLS VPNs)

6PE (IPv6 over MPLS without VPNs):

Uses global IPv6 routing over MPLS.

No VPN instances (VRFs) are created on PEs.

IPv6 addresses cannot be reused across different CEs because all traffic is routed using a single global table.

6VPE (IPv6 over MPLS with VPNs):

Uses MPLS VPN (VRF instances) to provide IPv6 VPN services.

VPN instances (VRFs) are created on PEs to separate customer networks.

IPv6 addresses of CEs can be reused in different VPN instances because each VRF maintains separate routing tables.

Correct Answer Explanation:

✅ C. In 6VPE networking, IPv6 addresses of a CE can be reused.

Since each VPN instance (VRF) maintains its own IPv6 routing table, IPv6 addresses of CEs can be reused across different VPNs.

Incorrect Answer Explanations:

❌ A. In 6PE networking, VPN instances need to be created on PEs.

Wrong! 6PE does not use VPN instances (VRFs); it relies on a global IPv6 routing table.

❌ B. In 6PE networking, IPv6 addresses of a CE can be reused.

Wrong! Since 6PE uses a single IPv6 global routing table, IPv6 addresses cannot be reused.

❌ D. In 6VPE networking, no VPN instance needs to be created on PEs.

Wrong! 6VPE requires VPN instances (VRFs) on PEs to separate customer traffic.

Reference from Huawei HCIE-Datacom Documentation:

Huawei MPLS VPN Configuration Guide – 6PE and 6VPE Deployment

HCIE-Datacom Training Material – IPv6 MPLS Solutions

Understanding the Routing Table Entries on R4

0.0.0.0/0 (Default Route) is installed twice in the routing table.

The NextHop values for the default route:

10.1.24.1 (GigabitEthernet0/0/1)

10.1.34.1 (GigabitEthernet0/0/0)

Cost: Both routes have a metric (Cost) of 10, meaning they are equal-cost routes.

Protocol: ISIS-L1 (Intermediate System to Intermediate System - Level 1) confirms these routes are coming from IS-IS routing.

Flags: D (Dynamic) means these routes were dynamically learned via IS-IS.

Why is Option D Correct?

Since both routes have the same cost (10), they are considered equal-cost default routes.

The router will use both routes in a load-sharing fashion.

The answer is NOT A (Four equal-cost routes) because there are only two default routes, not four.

The answer is NOT B (One default route) because there are two default routes in the table.

The answer is NOT C (Two default routes with different costs) because both routes have the same cost (10).

Real-World Application

Equal-Cost Multi-Path (ECMP): The router can perform load balancing across the two equal-cost paths.

Resilience & Redundancy: If one link fails, the other can take over without re-calculating the entire routing table.

✅ Reference: Huawei HCIE-Datacom Study Guide – IS-IS Routing & ECMP Load Balancing

Understanding 6PE & 6VPE in MPLS Networks

6PE (IPv6 Provider Edge) and 6VPE (IPv6 VPN Provider Edge) are MPLS-based solutions that allow IPv6 traffic to be carried over an MPLS IPv4 core network without requiring the entire backbone to support IPv6.

???? 6PE (IPv6 over MPLS - No VPN)

Used for global IPv6 routing without VPN segmentation.

No need for VRFs (VPN Routing and Forwarding instances) because IPv6 prefixes are handled natively.

???? 6VPE (IPv6 VPN over MPLS - Supports VPNs)

Extends MPLS L3VPN to support IPv6 routing inside VPN instances.

Uses MP-BGP VPNv6 to distribute IPv6 prefixes inside MPLS VPNs.

Why is the Answer TRUE?

✅ No VRFs are required for 6PE:

6PE only needs BGP labeled IPv6 routes in the global routing table.

IPv6 prefixes are carried using MPLS labels without VPN segmentation.

✅ VRFs are required for 6VPE, NOT for 6PE:

6VPE requires VPN instances (VRFs) for IPv6 L3VPNs, but 6PE does not.

✅ Real-World Application:

6PE is used in large ISP networks where IPv6 deployment is needed but without VPN separation.

6VPE is used for enterprise MPLS VPNs, allowing customers to have isolated IPv6 routing tables.

✅ Reference: Huawei HCIE-Datacom Guide – MPLS IPv6 Transition Technologies (6PE & 6VPE)