Understand Open Shortest Path First (ospf) Design Guide

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Understand Open Shortest Path First (OSPF)
- Design Guide
 
Contents
Introduction
Background Information
OSPF versus RIP
What Do We Mean by Link-States?
Shortest Path First Algorithm
OSPF Cost
Shortest Path Tree
Areas and Border Routers
Link-State Packets
Enable 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
the Backbone
Neighbors
Adjacencies
DR Election
Build the Adjacency
Adjacencies on Point-to-Point Interfaces
Adjacencies on Non-Broadcast Multi-Access (NBMA) Networks
Avoid DRs and neighbor Command on NBMA
Point-to-Point Subinterfaces
Select Interface Network Types
OSPF and Route Summarization
Inter-Area Route Summarization
External Route Summarization
Stub Areas
Redistribute Routes into OSPF
E1 vs. E2 External Routes
Redistribute OSPF into Other Protocols
Use of a Valid Metric
VLSM
Mutual Redistribution
Inject Defaults into OSPF
OSPF Design Tips
Number of Routers per Area

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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 Address
Appendix C: Variable Length Subnet Masks (VLSM)
Related Information
Introduction
This document describes how OSPF works and how it can be used to design and build large and
complicated networks.
Background Information
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.
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 the creation of 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