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Routing & Switching · Advanced

Segment Routing (SR)

A source-routing architecture where the ingress node encodes a path as an ordered list of segments, with no per-flow state in the core.

Definition

Segments are distributed by IS-IS, OSPF or BGP extensions, removing the need for LDP and RSVP-TE. SR-MPLS encodes segments as MPLS labels; SRv6 encodes them as IPv6 addresses. It enables traffic engineering, TI-LFA protection and controller-based path steering.

Example

segment-routing mpls under router isis on IOS XR

Exam tip

SR eliminates LDP and RSVP-TE; only the headend holds path state.

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