When segment routing is used together with MPLS data plane, the SID is a standard MPLS label. A router forwarding a packet using segment routing therefore pushes one or more MPLS labels.
Segment routing using MPLS labels can be used in both shortest path routing applications (see Segment routing in shortest path forwarding for more information) and in traffic engineering (TE) applications, as described in this section.
An SR-TE LSP supports a primary path, with Fast Reroute (FRR) backup, and one or more secondary paths. A secondary path can be configured as standby.
SR OS implements the following computation methods for the paths of a SR-TE LSP:
hop-to-label translation
See SR-TE LSP path computation using hop-to-label translation for more details.
local CSPF
See SR-TE LSP path computation using local CSPF for more details.
Path Computation Element (PCE)
See PCEP for more details.
user-specified SID list
See SR-TE LSP paths using explicit SIDs for more details.
The configured or computed path of a SR-TE LSP can use a combination of node SIDs and adjacency SIDs.