RFC 2328 OSPF Version 2 April 1998 Implementations of this memo and of RFCs 2178, 1583, and 1247 will interoperate. Please send comments to . Table of Contents 1 Introduction ........................................... 6 1.1 Protocol Overview ...................................... 6 1.2 Definitions of commonly used terms ..................... 8 1.3 Brief history of link-state routing technology ........ 11 1.4 Organization of this document ......................... 12 1.5 Acknowledgments ....................................... 12 2 The link-state database: organization and calculations 13 2.1 Representation of routers and networks ................ 13 2.1.1 Representation of non-broadcast networks .............. 15 2.1.2 An example link-state database ........................ 18 2.2 The shortest-path tree ................................ 21 2.3 Use of external routing information ................... 23 2.4 Equal-cost multipath .................................. 26 3 Splitting the AS into Areas ........................... 26 3.1 The backbone of the Autonomous System ................. 27 3.2 Inter-area routing .................................... 27 3.3 Classification of routers ............................. 28 3.4 A sample area configuration ........................... 29 3.5 IP subnetting support ................................. 35 3.6 Supporting stub areas ................................. 37 3.7 Partitions of areas ................................... 38 4 Functional Summary .................................... 40 4.1 Inter-area routing .................................... 41 4.2 AS external routes .................................... 41 4.3 Routing protocol packets .............................. 42 4.4 Basic implementation requirements ..................... 43 4.5 Optional OSPF capabilities ............................ 46 5 Protocol data structures .............................. 47 6 The Area Data Structure ............................... 49 7 Bringing Up Adjacencies ............................... 52 7.1 The Hello Protocol .................................... 52 7.2 The Synchronization of Databases ...................... 53 7.3 The Designated Router ................................. 54 7.4 The Backup Designated Router .......................... 56 7.5 The graph of adjacencies .............................. 56 Moy Standards Track