Google, Inc. Cisco Systems Cisco Systems Alcatel-Lucent Cisco Systems OSPF is a link-state intra-domain routing protocol. OSPF routers exchange information on a link using packets that follow a well-defined fixed format. The format is not flexible enough to enable new features that need to exchange arbitrary data. This document describes a backward-compatible technique to perform link-local signaling, i.e., exchange arbitrary data on a link. This document replaces the experimental specification published in RFC 4813 to bring it on the Standards Track.