OSPF DESIGN GUIDE

Author: Sam Halabi-Cisco Systems
Network Consulting Engineer - NSA group
Edited by Laura McCarty
Date: April 9, 1996
Rev: A1.0

The Open Shortest Path First Protocol (OSPF), defined in RFC 1583, 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. For any clarification or comments please send e-mail to shalabi@cisco.com.

Index

Section 1:

• 1.0 - Introduction
• 1.1 - OSPF vs. RIP
• 1.2 - What do we mean by Link-States?
• 1.3 - Link-State Algorithm
• 2.0 - Shortest Path Algorithm
• 2.1 - OSPF cost
• 2.2 - Shortest Path Tree
• 3.0 - Areas and Border Routers
• 4.0 - Link-State Packets
• 5.0 - Enabling OSPF on the router
• 6.0 - OSPF Authentication
• 6.1 - Simple password authentication
• 6.2 - Message Digest authentication
• 7.0 - The Backbone and area 0
• 8.0 - Virtual links
• 8.1 - Areas not physically connected to area 0
• 8.2 - Partitioning the backbone
• 9.0 - Neighbors
• 10.0 - Adjacencies
• 10.1 - DR Election
• 10.2 - Building the Adjacency
• 10.3 - Adjacencies on point-to-point interfaces
• 10.4 - Adjacencies on Non-Broadcast Multi-Access (NBMA)

Section 2:

• 11.0 - Avoiding DRs and "neighbor" command on NBMA
• 11.1 - Point-to-point subinterfaces
• 11.2 - Selecting Interface Network Types
• 11.2.1 - Point-to-multipoint interfaces
• 11.2.2 - Broadcast interfaces
• 12.0 - OSPF and Route Summarization
• 12.1 - Inter-area route summarization
• 12.2 - External route summarization
• 13.0 - Stub Areas
• 14.0 - Redistributing routes into OSPF
• 14.1 - E1 vs. E2 external routes
• 15.0 - Redistributing OSPF into other protocols
• 15.1 - Use of a valid metric
• 15.2 - VLSM
• 15.3 - Mutual Redistribution
• 16.0 - Injecting defaults into OSPF
• 17.0 - OSPF Design Tips
• 17.1 - Number of routers per area
• 17.2 - Number of neighbors
• 17.3 - Number of areas per ABR
• 17.4 - Full mesh vs. Partial Mesh
• 17.5 - Memory issues
• 18.0 - Summary

Section 3:

• 19.0 - APPENDIX A: Link-State Database Synchronization
• 19.1 - Link-State Advertisements
• 19.2 - OSPF database example
• 19.2.1 - General view of the data base
• 19.2.2 - Router Links
• 19.2.3 - Network Links
• 19.2.4 - Summary Links
• 19.2.5 - Summary ASBR Links
• 19.2.6 - External Links
• 19.2.7 - The Full Database
• 20.0 - APPENDIX B: OSPF and IP Multicast Addressing
• 21.0 - APPENDIX C: Variable Length Subnet Masks (VLSM)

Copyright 1996 © Cisco Systems Inc.