Instead of forwarding to a specific device or to all devices in a
group, anycast addresses, let network devices forward a packet to (or
steer it through) one or more topologically nearest devices in a
specific group of network devices. The use of anycast addresses has
been extended to the Segment Routing (SR) network, wherein a group of
SR-capable devices can represent a anycast address, by having the same
Segment Routing Global Block (SRGB) provisioned on all the devices and
each one of them advertising the same anycast prefix segment (or
Anycast SID). This document describes a proposal for implementing
anycast prefix segments in a MPLS-based SR network, without the need
to have the same SRGB block (label ranges) provisioned across all the
member devices in the group. Each node can be provisioned with a
separate SRGB from the label range supported by the specfic hardware
platform.