OSPF Area Design and Terms

By | August 28, 2017

Here are some core concepts that go into understanding OSPF.  This is the number one IGRP in the world so it worth taking time to understand a few of these fundamental principles.

  • The three tables used are the Neighbor table, the Topology table, and the Routing table.
  • All routers must connect to Area 0.  Routers in the same area will have the same topology table.
  • The more routers in an area, the larger the topology table therefore the more resources consumed on a router.  This becomes more of a concern as routers fail and topology updates occur.  Having area boundaries with ABR’s (Area Border Routers) will allow you to summarize routes from different areas.
  • Utilizing areas properly requires a hierarchical design.
  • Another type of router is an ASBR (Autonomous System Boundary Router) which bridges in routes from other routing protocols such as BGP, EIGRP, ISIS, RIP, etc.  This commonly happens with internet route distribution or in company mergers.
  • Most companies will break out area’s based on geography.  Having separate areas for separate regions can ensure the HQ location will be your Hub (the area 0).
  • Sometimes, situations will arise where not everything can connect to Area 0.  In these situations, virtual links can be used to trick other areas into thinking they are directly connected to Area 0.  It acts as a tunnel that allows you to tunnel an area through another area to reach area 0.  This is not good design but might be necessary in certain situations as networks grow and change.