http://www.rfc-editor.org/rfc/rfc5243.txt
RFC 5243: OSPF Database Exchange Summary List Optimization, R. Ogier2008-05-01T23:00:00-00:00This document describes a backward-compatible optimization for the Database Exchange process in OSPFv2 and OSPFv3. In this optimization, a router does not list a Link State Advertisement (LSA) in Database Description packets sent to a neighbor, if the same or a more recent instance of the LSA was listed in a Database Description packet already received from the neighbor. This optimization reduces Database Description overhead by about 50% in large networks. This optimization does not affect synchronization, since it only omits unnecessary information from Database Description packets. This memo provides information for the Internet community.