IETF RFC 9351 PDF

Flexible Algorithm is a solution that allows some routing protocols (e.g., OSPF and IS-IS) to compute paths over a network based on user-defined (and hence, flexible) constraints and metrics. The computation is performed by routers participating in the specific network in a distributed manner using a Flexible Algorithm Definition (FAD). This definition is provisioned on one or more routers and propagated through the network by OSPF and IS-IS flooding.

Border Gateway Protocol - Link State (BGP-LS) enables the collection of various topology information from the network. This document defines extensions to the BGP-LS address family to advertise the FAD as a part of the topology information from the network.