OSPF is an industry-standard routing protocol developed by the Internet Engineering Taskforce (IETF) as a replacement for legacy routing protocols that did not scale well in large environments. OSPF supports the following features:
• Variable-length subnet masks (VLSM).
• The use of areas to minimize Central Processing Unit (CPU) and memory requirements.
• A simple cost metric that you can manipulate to support up to six equal cost paths. The number of paths is limited only by the Internet Operating System (IOS).
• The use of authentication to ensure OSPF updates are secure and the use of multicast updates to conserve bandwidth.
• Faster convergence times ensuring updates and changes are propagated across the network.
• No limitation of network diameter or hop count. Limiting factors include only CPU and memory resources.
• The ability to tag OSPF information injected from any autonomous systems.
The following topics are covered in this section:
• Connecting multiple OSPF areas
• VLSM and summarization with OSPF
• OSPF over multiarea NBMA
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