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Question 61. In an MPLS network, what is the PRIMARY function of the ingress Label Edge Router (LER)?

1. To remove every label before the packet enters the MPLS domain
2. To operate only as a Layer 2 switch
3. To advertise DHCP leases to downstream routers
4. To classify incoming traffic into an FEC and push the appropriate MPLS label onto the packet

Correct Answer: 4. To classify incoming traffic into an FEC and push the appropriate MPLS label onto the packet

Explanation:

The ingress LER sits at the edge of an MPLS domain and receives ordinary packets from a non-MPLS network. It classifies packets into a Forwarding Equivalence Class and applies the appropriate MPLS label before forwarding them into the label-switched network. Core Label Switching Routers then forward traffic primarily by examining and swapping labels rather than repeatedly performing ordinary IP forwarding decisions. At the far end, the egress LER removes the MPLS label and forwards the original packet toward its destination. This push-swap-pop behavior is fundamental to MPLS forwarding.

Question 62. What is an MPLS Label Switched Path (LSP)?

1. A Layer 2 VLAN spanning-tree instance
2. A path through an MPLS domain along which packets are forwarded based on labels
3. A BGP peer relationship
4. A DHCP relay path

Correct Answer: 2. A path through an MPLS domain along which packets are forwarded based on labels

Explanation:

An MPLS Label Switched Path is a forwarding path established through a sequence of Label Switching Routers. Packets entering the MPLS domain are assigned labels, and each transit LSR uses its label-forwarding information to swap the incoming label for an outgoing label and forward the packet toward the next hop. The LSP terminates at an egress node, where the MPLS encapsulation is removed as required. LSPs can be built statically or dynamically using label-distribution mechanisms such as LDP. They form the forwarding foundation for many MPLS services, including Layer 3 VPNs.

Question 63. What is the PRIMARY purpose of LDP in an MPLS network?

1. To dynamically distribute labels and establish or maintain LSPs based on routing information
2. To elect the OSPF Designated Router
3. To assign VLAN IDs to Ethernet frames
4. To provide IPv6 Neighbor Discovery

Correct Answer: 1. To dynamically distribute labels and establish or maintain LSPs based on routing information

Explanation:

Label Distribution Protocol is an MPLS control-plane protocol used to classify forwarding equivalence classes, assign labels, distribute those labels between Label Switching Routers, and dynamically establish LSPs. LDP normally follows the path calculated by the underlying IGP, meaning the IP routing topology determines the forwarding path over which labels are distributed. Compared with manually configured static LSPs, LDP reduces configuration workload and the risk of inconsistent label assignments. A correctly operating IGP is therefore an important prerequisite for normal LDP-based MPLS forwarding.

Question 64. In MPLS forwarding, what does a transit LSR normally do when it receives a labeled packet?

1. Convert the packet into an OSPF Hello
2. Remove all Layer 3 addressing
3. Look up the incoming label, swap it for the appropriate outgoing label, and forward the packet
4. Send the packet directly to the DHCP server

Correct Answer: 3. Look up the incoming label, swap it for the appropriate outgoing label, and forward the packet

Explanation:

A transit Label Switching Router forwards MPLS packets by using label-forwarding information rather than making the same type of destination-IP lookup performed by ordinary IP forwarding. The device examines the incoming MPLS label, determines the outgoing interface and replacement label, swaps the label, and sends the packet toward the next LSR. This process continues until the packet reaches the end of the LSP. At the egress edge, the label is removed and normal forwarding resumes. Label switching provides the basic forwarding behavior that makes MPLS suitable for VPN, traffic-engineering, and service-provider applications.

Question 65. In a BGP/MPLS Layer 3 VPN, what is the PRIMARY purpose of a Route Distinguisher (RD)?

1. To make otherwise overlapping customer IPv4 prefixes unique in the VPN routing domain
2. To choose the STP root bridge
3. To determine the DHCP lease time
4. To identify the physical MPLS interface

Correct Answer: 1. To make otherwise overlapping customer IPv4 prefixes unique in the VPN routing domain

Explanation:

Different VPN customers may use identical private IPv4 prefixes, such as 10.0.0.0/8. BGP/MPLS L3VPN must therefore distinguish one customer’s route from another even when their IPv4 prefixes are identical. The Route Distinguisher is combined with the IPv4 route to create a unique VPN-IPv4 route representation. Huawei configuration guidance requires an RD for the VPN instance address family before that address family becomes operational. The RD provides uniqueness; it does not itself decide which VPN instances import or export the route. That policy function is handled by VPN targets.

Question 66. What is the PRIMARY function of a VPN Target (RT) in a BGP/MPLS IP VPN?

1. To identify the MPLS LSR ID
2. To calculate the IGP metric
3. To select a physical CE-PE interface
4. To control which VPN routes are exported from and imported into VPN instances**

Correct Answer: 4. To control which VPN routes are exported from and imported into VPN instances

Explanation:

A VPN Target, also called a Route Target, is a BGP extended community used to control VPN route distribution. A PE adds export VPN targets to VPN routes it advertises. When another PE receives those VPN routes, it compares the route’s export targets with the import targets configured for its VPN instances. If they match, the route can be imported into the corresponding VPN routing table. This makes RTs a flexible policy mechanism for building full-mesh, hub-and-spoke, or other VPN topologies. Unlike an RD, an RT controls route membership and distribution rather than uniqueness.

Question 67. Which statement correctly distinguishes an RD from an RT in an MPLS L3VPN?

1. Both perform exactly the same function
2. The RD provides route uniqueness, whereas the RT controls VPN route import and export policy
3. The RT provides route uniqueness, whereas the RD controls STP
4. The RD is used only for DHCP and the RT only for NAT

Correct Answer: 2. The RD provides route uniqueness, whereas the RT controls VPN route import and export policy

Explanation:

Route Distinguishers and Route Targets are both important in MPLS L3VPN, but they solve different problems. The RD is associated with a VPN instance so overlapping customer IPv4 prefixes can be represented uniquely in VPN routing. The RT is a BGP extended community used to control whether remote VPN routes are imported into or exported from a particular VPN instance. Confusing these two functions can cause major VPN design errors. An RD alone does not determine which customer sites exchange routes; the import and export RT relationship determines that policy.

Question 68. Which device in a traditional BGP/MPLS L3VPN normally connects directly to the customer CE and maintains VPN-instance information?

1. P router only
2. Access switch only
3. Provider Edge (PE) router
4. DHCP relay agent

Correct Answer: 3. Provider Edge (PE) router

Explanation:

The Provider Edge router sits at the boundary between the service-provider MPLS backbone and the customer network. It connects to one or more Customer Edge devices and maintains VPN-specific routing information in VPN instances. PE routers also participate in MPLS forwarding and exchange VPN routes with other PEs using the appropriate VPN address family. By contrast, core Provider routers generally do not need to maintain individual customer VPN routing tables; they mainly forward MPLS traffic across the provider backbone. This separation helps MPLS VPN architectures scale to many customers.

Question 69. What is the normal role of a Provider (P) router in an MPLS L3VPN backbone?

1. Maintain every customer’s VPN routing table
2. Connect directly to all customer LANs
3. Perform DHCP relay for every customer
4. Forward MPLS traffic across the provider core without needing customer VPN-instance information**

Correct Answer: 4. Forward MPLS traffic across the provider core without needing customer VPN-instance information

Explanation:

A Provider router is a core device inside the service-provider network. Huawei describes P routers as MPLS-capable Label Switching Routers that process MPLS forwarding but do not need to maintain customer VPN information because they are not directly connected to customer CE devices. This separation is one of the reasons BGP/MPLS VPN scales well: PE routers handle customer-specific routing, while P routers concentrate on backbone transport. In a normal VPN data path, the P router processes the outer transport label and does not need detailed knowledge of which customer prefix is carried inside the VPN packet.

Question 70. Why can two different MPLS VPN customers use the same IPv4 prefix without causing a routing conflict on a PE?

1. Separate VPN instances and RDs allow the PE to maintain logically distinct routing information
2. MPLS disables IP addressing
3. Every customer uses the same RT
4. The P router rewrites all customer addresses

Correct Answer: 1. Separate VPN instances and RDs allow the PE to maintain logically distinct routing information

Explanation:

MPLS L3VPN provides logical routing separation between customers. Each customer’s routes are stored in a separate VPN instance, and an RD is associated with the VPN address family to make overlapping customer routes unique when represented as VPN routes. Therefore, Customer A and Customer B can both use a prefix such as 10.1.1.0/24 without those routes becoming indistinguishable in the provider’s VPN control plane. RTs then determine which sites are allowed to exchange VPN routes. This combination of VPN instances, RDs, and RTs provides both isolation and flexible connectivity.

Question 71. In a BGP/MPLS IP VPN, what happens when a received VPN route’s export RT matches a local VPN instance’s import RT?

1. The route is discarded automatically
2. The route is converted into an STP BPDU
3. The route can be imported into that VPN instance’s routing table
4. The VPN instance is deleted

Correct Answer: 3. The route can be imported into that VPN instance’s routing table

Explanation:

When a PE receives a VPN route, it examines the VPN Target extended community attached to that route. If one of the route’s export RTs matches an import RT configured on a local VPN instance, the route is eligible to be placed into that instance’s routing table. If there is no matching import relationship, the route is not imported into that VPN. This matching mechanism gives administrators fine-grained control over which customer sites can exchange routes and is the foundation for flexible MPLS VPN topologies.

Question 72. What happens when a Huawei interface is bound to a VPN instance using ip binding vpn-instance?

1. The interface automatically becomes an MPLS P router
2. Existing Layer 3 features such as configured IP addresses may be removed and must be reconfigured as required
3. The interface becomes a Layer 2 access port permanently
4. BGP is automatically disabled globally

Correct Answer: 2. Existing Layer 3 features such as configured IP addresses may be removed and must be reconfigured as required

Explanation:

Huawei configuration documentation warns that the ip binding vpn-instance operation changes the interface’s Layer 3 context. When the interface is bound to a VPN instance, existing IPv4 and IPv6 Layer 3 settings, such as configured addresses or routing-protocol parameters, can be deleted and must be configured again if they are still needed. Administrators should therefore plan the command sequence carefully. A common workflow is to bind the interface to the VPN instance first and then configure the appropriate IP addressing and routing parameters within the resulting VPN context.

Question 73. In a typical MPLS VPN packet carried across the provider backbone, what is the function of the outer MPLS label?

1. Identify the transport LSP toward the remote PE
2. Identify the customer’s DHCP pool
3. Choose the STP instance
4. Store the BGP Local Preference

Correct Answer: 1. Identify the transport LSP toward the remote PE

Explanation:

Huawei describes a typical MPLS VPN packet as carrying an outer transport label and an inner VPN-related label. The outer label identifies the LSP used to transport the packet through the provider backbone toward the remote PE. Core P routers process this outer label as the packet moves through the MPLS network. The inner label is used closer to the egress PE to identify the VPN forwarding context associated with the packet. This two-label architecture allows core routers to transport multiple VPN services without maintaining every customer’s detailed routing table.

Question 74. What is the function of the inner MPLS label in a typical BGP/MPLS L3VPN packet?

1. It identifies the STP root switch
2. It represents the customer’s OSPF area
3. It carries a DHCP lease
4. It helps the egress PE identify the appropriate VPN forwarding context or VPN route**

Correct Answer: 4. It helps the egress PE identify the appropriate VPN forwarding context or VPN route

Explanation:

In a typical MPLS VPN packet, the outer label provides transport through the provider backbone, while the inner label identifies the VPN-specific forwarding context at the remote PE. When the packet reaches the egress side, the PE uses this VPN-related label and its VPN forwarding information to deliver traffic to the correct customer site. This separation enables many customers to share the same MPLS transport infrastructure while preserving logical isolation. Core P routers generally only need to process the outer transport label and do not need customer-specific VPN route information.

Question 75. What is the PRIMARY purpose of QoS on an IP network?

1. To guarantee that all traffic always receives identical treatment
2. To prioritize and manage traffic so important services receive suitable resources during congestion
3. To replace dynamic routing protocols
4. To disable packet buffering

Correct Answer: 2. To prioritize and manage traffic so important services receive suitable resources during congestion

Explanation:

Quality of Service is used when different applications have different sensitivity to delay, jitter, packet loss, and congestion. Huawei explains that QoS allows traffic to compete for network resources according to priority so services such as voice, video, and business-critical data can receive preferential treatment. QoS does not create unlimited bandwidth, but it helps use existing network resources more effectively. A complete QoS design typically includes traffic classification, marking, policing or shaping, queue management, and scheduling according to service requirements.

Question 76. Which traffic type generally requires the most stringent delay and jitter treatment from QoS?

1. Large overnight backup transfers
2. Bulk software downloads
3. Real-time voice traffic
4. Background file synchronization

Correct Answer: 3. Real-time voice traffic

Explanation:

Real-time voice is highly sensitive to delay and variation in packet arrival time. Excessive latency can make conversation difficult, while jitter can lead to choppy or distorted audio if buffers cannot compensate adequately. Huawei notes that real-time services such as voice have strong requirements for stable network quality and are more sensitive to congestion than many non-real-time applications. QoS policies often classify voice into a high-priority service class and provide appropriate queue scheduling so delay-sensitive packets are processed promptly during congestion.

Question 77. What is the PRIMARY purpose of CPCAR on a Huawei device?

1. To create VPN instances
2. To control BGP path selection
3. To translate private IP addresses
4. To rate-limit traffic sent to the device CPU so excessive protocol traffic cannot overwhelm control-plane processing**

Correct Answer: 4. To rate-limit traffic sent to the device CPU so excessive protocol traffic cannot overwhelm control-plane processing

Explanation:

Control Plane Committed Access Rate protects the device CPU from excessive protocol or control-plane traffic. Huawei explains that CPCAR can set rate limits for different protocols so one traffic type does not consume CPU resources needed by other critical protocols. Packets exceeding the configured rate can be discarded, and traffic can also be placed into queues that are scheduled according to weight or priority. This helps preserve control-plane stability during traffic bursts, attacks, or protocol abnormalities and is therefore an important network-device security and reliability mechanism.

Question 78. Why does Huawei CPCAR use different protocol queues and priorities?

1. To ensure higher-priority control-plane services can be processed preferentially when CPU resources are contested
2. To replace packet forwarding in the data plane
3. To calculate MPLS VPN Route Distinguishers
4. To create VLAN trunks

Correct Answer: 2. To ensure higher-priority control-plane services can be processed preferentially when CPU resources are contested

Explanation:

Rate limiting alone may not be sufficient when multiple control-plane protocols simultaneously generate large volumes of traffic. Huawei CPCAR therefore supports queue-based scheduling in addition to protocol-specific rate limits. Different categories of control-plane traffic can be placed into different queues, and higher-priority queues are more likely to receive CPU processing when contention occurs. For example, critical routing or management traffic may need to be processed ahead of less important packets. This protects the stability of the device’s control plane under abnormal load.

Question 79. What is an LSP ping test primarily used to verify?

1. Reachability of an MPLS LSP
2. VLAN membership of a switch port
3. DHCP server authorization
4. WLAN client roaming

Correct Answer: 1. Reachability of an MPLS LSP

Explanation:

Huawei NQA includes an LSP ping capability that checks reachability of LDP or traffic-engineering LSPs. The source sends an MPLS Echo Request along the label-switched path and waits for the corresponding MPLS Echo Reply. The response allows the device to determine whether the LSP is reachable and to measure round-trip timing. This is useful when ordinary IP reachability appears normal but administrators suspect a problem in the MPLS forwarding path. LSP trace can provide additional hop-by-hop information about the path taken through the MPLS domain.

Question 80. A service provider wants customer route isolation, support for overlapping private prefixes, selective site-to-site route sharing, labeled backbone forwarding, and preferential treatment for latency-sensitive VPN traffic. Which design BEST satisfies these requirements?

1. Use one global routing table and disable MPLS
2. Use VLANs only and advertise all customer routes together
3. Use BGP/MPLS L3VPN with separate VPN instances, RDs for route uniqueness, RTs for route import/export, MPLS transport labels, and QoS for sensitive traffic
4. Use only static NAT rules

Correct Answer: 3. Use BGP/MPLS L3VPN with separate VPN instances, RDs for route uniqueness, RTs for route import/export, MPLS transport labels, and QoS for sensitive traffic

Explanation:

The requirements align directly with BGP/MPLS L3VPN architecture. Separate VPN instances isolate customer routing tables. Route Distinguishers make overlapping customer prefixes unique in VPN routing, while VPN Targets control which sites import and export routes. MPLS LSPs provide labeled transport through the provider backbone, allowing P routers to forward VPN traffic without maintaining customer routing information. QoS can then classify and prioritize delay-sensitive services such as voice during congestion. Together, these functions provide scalable multi-customer VPN service with isolation, flexible connectivity, and differentiated service treatment.