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Unformatted text preview: OSPF Design Guide Document ID: 7039 Contents Introduction Background Information OSPF versus RIP What Do We Mean by Link- States? Link- State Algorithm Shortest Path Algorithm OSPF Cost Shortest Path Tree Areas and Border Routers Link- State Packets Enabling OSPF on the Router OSPF Authentication Simple Password Authentication Message Digest Authentication The Backbone and Area 0 Virtual Links Areas Not Physically Connected to Area 0 Partitioning the Backbone Neighbors Adjacencies DR Election Building the Adjacency Adjacencies on Point- to- Point Interfaces Adjacencies on Non- Broadcast Multi- Access (NBMA) Networks Avoiding DRs and neighbor Command on NBMA Point- to- Point Subinterfaces Selecting Interface Network Types OSPF and Route Summarization Inter- Area Route Summarization External Route Summarization Stub Areas Redistributing Routes into OSPF E1 vs. E2 External Routes Redistributing OSPF into Other Protocols Use of a Valid Metric VLSM Mutual Redistribution Injecting Defaults into OSPF OSPF Design Tips Number of Routers per Area TAC Notice: What's C han g i n g o n T A C We b H el p u s h el p y ou . Please rate this d o c u m en t. n m l k j Excellent n m l k j G o o d n m l k j A v er a g e n m l k j F a i r n m l k j P o o r T his d o c u m en t so lv ed m y p ro b lem . n m l k j Y es n m l k j N o n m l k j J u s t b r o w s i ng S u g g estio n s f o r im p ro v em en t: ( 2 5 6 ch a r a cter li m i t) Send Page 1 of 58 Cisco - OSPF Design Guide 4/7/2006 http://www.cisco.com/warp/customer/104/1.html Number of Neighbors Number of Areas per ABR Full Mesh vs. Partial Mesh Memory Issues Summary Appendix A: Link- State Database Synchronization Link- State Advertisements OSPF Database Example Appendix B: OSPF and IP Multicast Addressing Appendix C: Variable Length Subnet Masks (VLSM) NetPro Discussion Forums - Featured Conversations Related Information Introduction The Open Shortest Path First (OSPF) protocol, defined in RFC 2328 , is an Interior Gateway Protocol used to distribute routing information within a single Autonomous System. This paper examines how OSPF works and how it can be used to design and build today's large and complicated networks. Background Information OSPF protocol was developed due to a need in the internet community to introduce a high functionality non-proprietary Internal Gateway Protocol (IGP) for the TCP/IP protocol family. The discussion of creating a common interoperable IGP for the Internet started in 1988 and did not get formalized until 1991. At that time the OSPF Working Group requested that OSPF be considered for advancement to Draft Internet Standard. The OSPF protocol is based on link-state technology which is a departure from the Bellman-Ford vector based algorithms used in traditional Internet routing protocols such as RIP. OSPF has introduced new concepts such as authentication of routing updates, Variable Length Subnet Masks (VLSM), route summarization, etc....
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- Fall '09