SRGB stands for Segment Routing Global Block. SRGB is a local property of a node and identifies labels reserved for global segments.
In the MPLS Data Plane, Prefix-SIDs are allocated from Segment Routing Global Block (SRGB). It can be hard coded or it may be indexed to the SRGB.
During the control plane advertisements both SRGB and Prefix-SID index are advertised to the other nodes for their Prefix-SID calculation.
In SR-MPLS, using identical SRGBs on all nodes within the SR domain is strongly recommended.
