View Full Huawei H12-821 Exam Dumps and Practice Test Dumps.

Question 201. What is the PRIMARY purpose of MPLS Traffic Engineering (MPLS TE)?

1. To replace all IP addressing with MPLS labels
2. To steer traffic over paths that satisfy constraints such as bandwidth or administrative requirements
3. To prevent routers from exchanging topology information
4. To provide only Layer 2 loop prevention

Correct Answer: 2. To steer traffic over paths that satisfy constraints such as bandwidth or administrative requirements

Explanation:

MPLS Traffic Engineering allows network operators to control how traffic crosses an MPLS network instead of relying solely on the shortest path calculated by a conventional IGP. A TE tunnel can be built according to requirements such as available bandwidth, link attributes, or an explicitly defined route. This makes MPLS TE useful when shortest-path forwarding would overload some links while other network capacity remains underused. Traffic engineering can therefore improve resource utilization, provide predictable paths for important services, and help meet service-level objectives. RSVP-TE is one mechanism that can establish MPLS TE LSPs while taking resource constraints into account.

Question 202. What is RSVP-TE primarily used for in an MPLS network?

1. To assign IPv6 addresses to MPLS routers
2. To calculate STP forwarding states
3. To replace every IGP
4. To signal MPLS traffic-engineered LSPs and reserve required network resources

Correct Answer: 4. To signal MPLS traffic-engineered LSPs and reserve required network resources

Explanation:

RSVP-TE is an extension of the Resource Reservation Protocol designed specifically for MPLS Traffic Engineering. It adds objects that allow routers to establish label-switched paths while considering constraints such as bandwidth and link affinity. RSVP itself manages resource reservation rather than calculating ordinary routing paths. RSVP-TE extends that model so labels can also be requested and distributed during signaling. This enables an MPLS TE tunnel to follow a path that has sufficient resources and satisfies policy requirements instead of automatically using only the normal IGP shortest path.

Question 203. Which RSVP-TE message travels from the ingress toward the egress to initiate LSP signaling?

1. Path message
2. Resv message
3. BGP UPDATE
4. OSPF Hello

Correct Answer: 1. Path message

Explanation:

RSVP-TE begins signaling with a Path message transmitted from the sender or ingress toward the receiver or egress along the intended path. The Path message carries information required for resource reservation and, in RSVP-TE, includes extensions such as a Label_Request object. After the Path message reaches the destination, the reservation phase proceeds in the reverse direction using a Resv message. This two-direction exchange allows devices along the path to establish forwarding and resource state. Path messages therefore initiate the signaling process, while Resv messages complete the reverse reservation and label-distribution phase.

Question 204. Which RSVP-TE message is sent back toward the ingress to complete resource reservation and distribute label information?

1. Hello
2. Notification
3. Resv
4. Keepalive

Correct Answer: 3. Resv

Explanation:

After an RSVP or RSVP-TE Path message travels toward the destination, the destination responds using a Resv message along the reverse path. In RSVP-TE, the Resv message can carry the Label object used for label distribution as the MPLS LSP is established. Devices along the route create the appropriate reservation and forwarding state as the message travels toward the ingress. This mechanism differs from protocols such as LDP, which distribute labels based primarily on forwarding equivalence classes and normal routing information rather than explicit traffic-engineering resource reservations.

Question 205. What is the PRIMARY role of CSPF in MPLS Traffic Engineering?

1. To encrypt MPLS packets
2. To advertise BGP communities
3. To create DHCP leases
4. To calculate a path that satisfies configured TE constraints rather than simply choosing an unconstrained shortest path

Correct Answer: 4. To calculate a path that satisfies configured TE constraints rather than simply choosing an unconstrained shortest path

Explanation:

Constraint-Based Shortest Path First extends normal shortest-path calculation by considering additional traffic-engineering requirements. These constraints can include available bandwidth, administrative link characteristics, and other TE attributes. A path that is shortest according to the IGP may not have sufficient resources for a new service, so CSPF can select another feasible route. Huawei documentation also notes that explicit paths can be configured when deterministic TE forwarding is required. CSPF is therefore a path-computation mechanism, not a packet-encryption or addressing technology.

Question 206. Why might an administrator configure an explicit path for an MPLS TE tunnel?

1. To force all routers to use the same router ID
2. To control the exact or preferred sequence of nodes or links used by the TE tunnel
3. To disable MPLS labels
4. To convert the tunnel into a VLAN

Correct Answer: 2. To control the exact or preferred sequence of nodes or links used by the TE tunnel

Explanation:

An explicit path gives the administrator direct control over the nodes or links that an MPLS TE tunnel should traverse. This can be useful when traffic must avoid a congested region, follow a planned engineering path, or satisfy operational requirements that cannot be expressed simply through standard IGP metrics. Huawei documentation recommends explicit-path configuration in situations where automatic TE path calculation may not produce the expected result. Explicit paths therefore provide deterministic path steering while still allowing MPLS label switching to carry traffic over the selected route.

Question 207. What is Segment Routing (SR)?

1. A source-routing approach in which an ingress node inserts an ordered set of segments that guide packet forwarding
2. A Layer 2 protocol used only to prevent Ethernet loops
3. A replacement for all IP addresses
4. A DHCP-based routing protocol

Correct Answer: 1. A source-routing approach in which an ingress node inserts an ordered set of segments that guide packet forwarding

Explanation:

Segment Routing is based on a source-routing model. A path is divided into segments, and the ingress node places an ordered list of segment instructions into the packet or associated forwarding information. Intermediate nodes then process those instructions to move the packet toward its destination. Huawei supports both SR-MPLS, which maps segments to MPLS labels, and SRv6, which represents segments using IPv6 mechanisms. One important advantage of SR is that transit routers do not need to maintain the same amount of per-path signaling state required by some traditional TE mechanisms.

Question 208. What is a Segment Identifier (SID) in Segment Routing?

1. The physical MAC address of the ingress router
2. An OSPF area number
3. An identifier representing a segment or forwarding instruction in the SR domain
4. A DHCP transaction ID

Correct Answer: 3. An identifier representing a segment or forwarding instruction in the SR domain

Explanation:

A SID identifies a segment within a Segment Routing domain. A segment represents a forwarding instruction, such as reaching a particular node or using a particular adjacency. In SR-MPLS, a SID is represented through MPLS label values in the forwarding plane. Huawei documents several SID types, including prefix SIDs, node SIDs, and adjacency SIDs. By arranging SIDs in a specific order, the ingress device can encode the intended forwarding path without requiring every intermediate router to maintain dedicated end-to-end tunnel state.

Question 209. What does a Node SID represent in SR-MPLS?

1. An instruction to reach a particular router, commonly associated with its loopback prefix
2. A particular Ethernet frame
3. A DHCPv6 delegated prefix
4. A physical VLAN ID

Correct Answer: 1. An instruction to reach a particular router, commonly associated with its loopback prefix

Explanation:

A Node SID represents a network node and is typically associated with the IP prefix of a router’s loopback interface. Huawei describes a node SID as a special type of prefix SID. When a packet carries that SID, the network forwards it toward the associated router using the normal shortest-path information calculated by the IGP, unless additional SR instructions alter the path. Node SIDs are globally meaningful within the intended SR domain, which makes them useful building blocks for constructing segment lists that steer traffic through selected routers.

Question 210. What does an Adjacency SID represent in SR-MPLS?

1. A complete autonomous system
2. Every equal-cost path to a destination
3. A VXLAN tenant network
4. A specific local adjacency or outgoing link that the packet should use

Correct Answer: 4. A specific local adjacency or outgoing link that the packet should use

Explanation:

An adjacency SID represents a specific link or adjacency on a router. It can therefore force a packet to leave the router through a particular interface toward a specific neighbor rather than simply following the default shortest path. Huawei notes that adjacency SIDs are local to the advertising device and are conceptually similar to explicitly identifying an outbound interface in conventional forwarding. Combining node and adjacency SIDs allows Segment Routing to build highly controlled paths while still using the standard MPLS forwarding plane.

Question 211. What is a Segment List in Segment Routing?

1. A list of VLAN IDs permitted on a trunk
2. A BGP community sequence
3. An ordered set of SIDs that defines the forwarding instructions for a packet
4. A list of DHCP clients

Correct Answer: 3. An ordered set of SIDs that defines the forwarding instructions for a packet

Explanation:

A segment list is an ordered collection of Segment Identifiers that defines how traffic should traverse the SR network. Each SID represents a forwarding instruction, such as reaching a particular node or taking a particular link. In SR-MPLS, Huawei explains that the segment list can be represented as an MPLS label stack. The ingress node applies this stack to the packet, and each router processes the active label or SID as forwarding progresses. By changing the segment list, the ingress can program different paths without requiring hop-by-hop tunnel signaling on every intermediate router.

Question 212. What is the Segment Routing Global Block (SRGB)?

1. A group of IPv6 multicast addresses
2. A reserved label range used for globally significant SR-MPLS prefix and node SIDs
3. A BGP route-reflector cluster
4. A group of physical MPLS interfaces

Correct Answer: 2. A reserved label range used for globally significant SR-MPLS prefix and node SIDs

Explanation:

The SRGB is a range of MPLS labels reserved for Segment Routing. Huawei explains that this range is used for globally significant prefix and node SIDs. Routers map SID index information into actual MPLS label values based on the configured SRGB. Adjacency SIDs are different because they are local SIDs and do not rely on the same globally coordinated label interpretation. Correct SRGB planning is important because inconsistent label interpretation can prevent devices from forwarding SR-MPLS traffic as intended.

Question 213. Which routing protocols can advertise SR-MPLS topology and SID information on Huawei networks?

1. Only BGP
2. Only RIP
3. DHCP and ARP
4. IGPs such as IS-IS or OSPF with Segment Routing extensions

Correct Answer: 4. IGPs such as IS-IS or OSPF with Segment Routing extensions

Explanation:

SR-MPLS commonly relies on an Interior Gateway Protocol to distribute topology and Segment Routing information. Huawei documentation describes IS-IS and OSPF support for SR-MPLS, including advertisement of topology, prefix information, SRGB information, and labels or SID-related data. This allows participating routers to build consistent forwarding information for Segment Routing. Unlike RSVP-TE, which establishes tunnels using a separate resource-reservation signaling protocol, SR can simplify the control plane by extending an existing IGP to advertise the information needed for SR forwarding.

Question 214. What is a significant control-plane advantage of SR-MPLS compared with traditional RSVP-TE?

1. Transit routers do not need to maintain the same amount of per-tunnel signaling state
2. SR-MPLS cannot perform path steering
3. SR-MPLS removes MPLS labels entirely
4. SR-MPLS requires a dedicated RSVP session for every segment

Correct Answer: 1. Transit routers do not need to maintain the same amount of per-tunnel signaling state

Explanation:

One of the major benefits of Segment Routing is control-plane simplification. The ingress router places the intended path instructions in the segment list, while transit routers primarily process the active SID or MPLS label. They do not need to maintain the same type of per-LSP RSVP-TE signaling state for every engineered path. Huawei identifies reduced control-plane complexity and easier path programming as important SR-MPLS benefits. The design also reuses the established MPLS forwarding plane, allowing SR to provide traffic engineering and SDN-oriented programmability without requiring an entirely new forwarding architecture.

Question 215. What happens when an SR-MPLS router receives a packet whose top SID identifies the local node?

1. The router discards the packet
2. The router processes or removes the active SID and continues with the next forwarding instruction
3. The router converts the packet to STP
4. The router sends the packet back to the ingress

Correct Answer: 2. The router processes or removes the active SID and continues with the next forwarding instruction

Explanation:

In SR-MPLS, the top label represents the active Segment Identifier. Huawei explains that if this SID identifies the receiving node, that node removes or processes the active SID and then continues according to the remaining segment list. This resembles MPLS label-stack processing, where completing one instruction reveals the next label beneath it. If the SID does not identify the local node, the packet is forwarded toward the node or segment represented by that SID, potentially using ECMP where valid. This ordered processing implements the source-programmed path.

Question 216. If an SR-MPLS Node SID can be reached through multiple equal-cost IGP paths, what forwarding behavior may occur?

1. The packet must be dropped because a SID allows only one link
2. The router must convert the Node SID into an adjacency SID
3. ECMP can be used across equal-cost paths toward the node represented by the SID
4. RSVP-TE must always be started first

Correct Answer: 3. ECMP can be used across equal-cost paths toward the node represented by the SID

Explanation:

A Node SID identifies a destination node rather than necessarily identifying one exact outgoing interface. Therefore, the underlying IGP shortest-path calculation may produce several equal-cost next hops toward the node. Huawei’s SR-MPLS documentation notes that forwarding toward a SID can use ECMP when the active SID does not identify the local node and multiple equal-cost forwarding paths exist. If the operator needs to force traffic onto one particular link rather than any equal-cost path, an adjacency SID or another more explicit segment list can be used.

Question 217. Which statement correctly distinguishes SR-MPLS from SRv6?

1. SR-MPLS uses MPLS labels for SIDs, whereas SRv6 uses IPv6-based segment information
2. SRv6 always requires MPLS labels
3. SR-MPLS works only on Ethernet Layer 2 networks
4. There is no forwarding-plane difference between them

Correct Answer: 2. SR-MPLS uses MPLS labels for SIDs, whereas SRv6 uses IPv6-based segment information

Explanation:

Segment Routing supports two major forwarding-plane implementations. SR-MPLS maps Segment Identifiers to MPLS labels and uses an MPLS label stack as the segment list. SRv6 operates using the IPv6 forwarding plane and carries segment information through IPv6 mechanisms such as the Segment Routing Header. Both implement the same overall source-routing idea: the ingress encodes the path or functions that traffic should follow. The key difference is the forwarding-plane representation. SR-MPLS can build on existing MPLS deployments, while SRv6 takes advantage of IPv6 extensibility.

Question 218. Why is SR-MPLS considered well suited to SDN-oriented networks?

1. It prevents centralized controllers from influencing paths
2. It requires every transit router to store every application flow
3. It removes traffic engineering
4. It allows programmable paths to be expressed at the ingress using segment lists while keeping transit forwarding comparatively simple

Correct Answer: 4. It allows programmable paths to be expressed at the ingress using segment lists while keeping transit forwarding comparatively simple

Explanation:

SR-MPLS supports path programmability because the desired forwarding behavior can be encoded as an ordered list of segments at the ingress. A centralized controller can therefore calculate a path that meets application or service requirements and instruct the ingress to apply an appropriate segment list. Transit nodes continue to perform relatively simple MPLS forwarding operations rather than maintaining extensive application-specific tunnel state. Huawei highlights SR’s compatibility with both distributed routing and centralized SDN control as an important advantage for service-driven network evolution.

Question 219. Which SR-MPLS SID type should be used when traffic must traverse one particular link even though another equal-cost link exists?

1. Prefix SID only
2. Node SID only
3. Adjacency SID
4. VLAN SID

Correct Answer: 3. Adjacency SID

Explanation:

A node SID or ordinary prefix SID generally forwards traffic toward a node according to the IGP’s shortest-path calculation, potentially using multiple equal-cost links. If the operator must force traffic over one specific adjacency, an adjacency SID is more appropriate. Huawei describes an adjacency SID as representing a designated local interface or link to a particular neighbor. By placing that SID in the segment list, the ingress can explicitly steer packets over the required link instead of allowing ordinary ECMP behavior to choose among several equivalent links.

Question 220. A provider wants engineered MPLS paths but also wants to reduce per-tunnel signaling state and support SDN-based path programming. Which design BEST addresses this requirement?

1. Use SR-MPLS with IGP-advertised SIDs and controller- or ingress-defined segment lists, using Node and Adjacency SIDs as needed
2. Build one large Layer 2 STP domain
3. Use DHCP relay to select MPLS paths
4. Disable MPLS and configure only default routes

Correct Answer: 1. Use SR-MPLS with IGP-advertised SIDs and controller- or ingress-defined segment lists, using Node and Adjacency SIDs as needed

Explanation:

SR-MPLS directly addresses the requirement for programmable traffic-engineered paths with a simpler control plane. IGP extensions such as IS-IS or OSPF can advertise topology and Segment Routing information, while the ingress or a controller determines the appropriate segment list. Node SIDs can steer traffic through selected routers, and adjacency SIDs can force particular links where tighter control is necessary. Because the forwarding instructions are encoded at the ingress, transit nodes do not require the same level of per-tunnel signaling state associated with RSVP-TE. This makes SR-MPLS attractive for scalable, SDN-oriented MPLS networks.