H12-831_V1-0 practice question 17 of 35

MPLS is called Multi-Protocol Label Switching. Regarding the label description in MPLS, the correct one is:

Domain MPLS Basics

Answer options

A: MPLSThe system has a variety of label publishing protocols, such asLDPis a label publishing agreement Correct answer

B: Labeled byMIPLSheader of messageBIt has global significance, that is, the label values of all routers cannot be repeated.

C: A label is a fixed-length identifier with only local significance, which is used to uniquely identify the group to which a group belongs.FEC Correct answer

D: MPLSSupports single-layer labels as well as multi-layer labels Correct answer

Correct Answer:

A. MPLSThe system has a variety of label publishing protocols, such asLDPis a label publishing agreement; C. A label is a fixed-length identifier with only local significance, which is used to uniquely identify the group to which a group belongs.FEC; D. MPLSSupports single-layer labels as well as multi-layer labels

Explanation

MPLS architecture is defined by several key characteristics. It uses various label distribution protocols, with the Label Distribution Protocol (LDP) being a primary example, to create and manage label bindings for Forwarding Equivalence Classes (FECs). A label is a short, fixed-length identifier that has only local significance between two adjacent Label Switched Routers (LSRs). It is not globally unique. A fundamental and powerful feature of MPLS is its support for a "label stack," which allows multiple labels to be imposed on a single packet. This enables hierarchical routing and tunneling for services like MPLS VPNs and Traffic Engineering.

Why Incorrect

B: MPLS labels have local significance, meaning they are only meaningful on the link between two adjacent routers. The same label value can be reused elsewhere in the network.

References

1. Huawei HCIP-Datacom-Core Technology V1.0 Training Material: In the "MPLS Principles" chapter, the material states, "LDP is one of the most widely used label distribution protocols" (supporting option A). It also clarifies, "An MPLS label has only local significance" (refuting option B and supporting option C) and describes the MPLS header format which includes the S-bit to indicate the bottom of the label stack, confirming multi-layer label support (supporting option D).

2. IETF RFC 3031, "Multiprotocol Label Switching Architecture":

Section 2.1, "Forwarding Equivalence Classes": Defines an FEC as a group of packets forwarded in the same manner, which a label represents. (Supports option C).

Section 3, "Labels": States, "A label is a short, fixed length, locally significant identifier...". This directly supports option C and refutes option B.

Section 3.15, "The Label Stack": Explicitly defines the concept of a stack of labels, which is the basis for multi-layer labels. (Supports option D).

3. IETF RFC 5036, "LDP Specification":

Section 1, "Introduction": Describes the Label Distribution Protocol (LDP) as a protocol for distributing labels between LSRs. (Supports option A).

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