OSPF Design: 3 – Fundamentals

OSPF benefits
  • Fast convergence
  • Variable-length subnet masking (VLSM)
  • Authentication
  • Hierarchical segmentation
  • Route summarization
  • Aggregation

Routing Summarization is a major factor in the success of designing your network. To ensure that your network can scale properly, route summarization is the biggest factor against which to measure your success. Without summarization, you have a flat address design with specific route information for every subnet being transmitted across the network—a bad thing in large networks.

Route Summarization - Network Stability

The six time-proven steps to designing a network are as follows:

  1. Analyze the requirements.
  2. Develop the network topology.
  3. Determine the addressing and naming conventions.
  4. Provision the hardware.
  5. Deploy protocol and Cisco IOS Software features.
  6. Implement, monitor, and maintain the network.

Consider the following issues when working through the network design process: Continue reading “OSPF Design: 3 – Fundamentals”

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OSPF Design: 2 – Introduction

A dynamic routing protocol supports a routed protocol and maintains routing tables.

The most common use of static routes is in stub networks.

In Link-State routing protocols, each router sends only that portion of the routing table that describes the state of its own links.

Link-state protocols are based on the distributed map concept, which means that every router has a copy of the network map that is regularly updated.

The principle of link-state routing is that all the routers within an area maintain an identical copy of the network topology.

Link-state protocols such as OSPF flood all the routing information when they first become active in link-state packets. After the network converges, they send only small updates via link-state packets.

In OSPF, because each router knows the complete topology of the network, the use of the SPF algorithm creates an extremely fast convergence.

  • Sends updates to tables only, instead of entire tables, to routers.
  • Is a more economical routing protocol than RIP over time because it involves less network traffic.

During an external convergence event, OSPF could flood more traffic than RIP. Consider that RIP carries 25 routes per update; on the other hand, OSPF floods a single LSA per external route that is affected by the convergence event.

Distance vector means that information sent from router to router is based on an entry in a routing table that consists of the distance and vector to destination—distance being what it “costs” to get there and vector being the “direction” to get to the destination.

Call for each router to send its entire routing table, but only to its neighbors. The neighbor then forwards its entire routing table to its neighbors, and so.

Distance Vector Operations

Continue reading “OSPF Design: 2 – Introduction”

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