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350-501 · Question #252

What is a characteristic of prefix segment identifier?

The correct answer is C. It is globally unique. A prefix segment identifier (Prefix SID) in Segment Routing identifies an IP prefix and is designed to be globally unique within a Segment Routing domain. This global uniqueness ensures consistent forwarding behavior across the network.

MPLS and Segment Routing

Question

What is a characteristic of prefix segment identifier?

Options

  • AIt contains a router to a neighbor
  • BIt contains the interface address of the device per each link
  • CIt is globally unique.
  • DIt is locally unique.

How the community answered

(50 responses)
  • A
    4% (2)
  • B
    6% (3)
  • C
    88% (44)
  • D
    2% (1)

Why each option

A prefix segment identifier (Prefix SID) in Segment Routing identifies an IP prefix and is designed to be globally unique within a Segment Routing domain. This global uniqueness ensures consistent forwarding behavior across the network.

AIt contains a router to a neighbor

A Prefix SID does not contain a router to a neighbor; rather, it identifies a destination prefix within the network.

BIt contains the interface address of the device per each link

A Prefix SID does not contain the interface address of a device; that is typically handled by adjacency SIDs or IP addressing itself.

CIt is globally unique.Correct

A prefix segment identifier (Prefix SID) is a globally unique label in a Segment Routing domain. It identifies an IP prefix that is advertised by a router, allowing any router in the domain to forward traffic towards that prefix using the associated SID. This global uniqueness is fundamental to Segment Routing's ability to orchestrate paths without per-node state.

DIt is locally unique.

A Prefix SID is not locally unique; its strength lies in being globally unique within the Segment Routing domain for consistent path computation.

Concept tested: Segment Routing Prefix SID characteristics

Source: https://www.cisco.com/c/en/us/td/docs/iosxr/cisco_iosxr_software/segment_routing/segment_routing_sr/config_guide/b-segment-routing-sr-cg-iosxr-73x/b-segment-routing-sr-cg-iosxr-73x_chapter_01.html

Topics

#Segment Routing#Prefix SID#Global Uniqueness

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