IETF RFC 9339 PDF

This document specifies the extensions to OSPF that enable a router to use Link-Local Signaling (LLS) to signal the metric that receiving OSPF neighbor(s) should use for a link to the signaling router. When used on the link to the signaling router, the signaling of this reverse metric (RM) allows a router to influence the amount of traffic flowing towards itself. In certain use cases, this enables routers to maintain symmetric metrics on both sides of a link between them.