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Routing & Switching · Advanced

Segment Identifier (SID)

An identifier for a segment: an MPLS label in SR-MPLS or an IPv6 address in SRv6.

Definition

Global SIDs (prefix, node, anycast) are understood network-wide; local SIDs (adjacency) are meaningful only on the originating router. Prefix SIDs are typically configured as an index added to the SRGB base.

Example

prefix-sid index 1 on Loopback0 gives label 16001 with SRGB 16000-23999.

Exam tip

Prefix SID = global, follows ECMP shortest path; adjacency SID = local, forces a specific link.

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