IGP Flexible Algorithms (Flex-Algorithm) In IP Networks

An IGP Flexible Algorithm (Flex-Algorithm) allows IGP to compute constraint-based paths. As currently defined, IGP Flex-Algorithm is used with Segment Routing (SR) data planes - SR MPLS and SRv6. Therefore, Flex-Algorithm cannot be deployed in the absence of SR. This document extends IGP Flex-Algorithm, so that it can be used for regular IPv4 and IPv6 prefixes. This allows Flex-Algorithm to be deployed in any IP network, even in the absence of SR.