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Appendix A: Data communications planning 10-101
Planning Guide NT6Q92MA Rel 1.0 Iss 1 Standard September 2006
Figure 10-28
OSPF areas
Wherever possible the DCN network should be fitted into one area (area 0).
This gives the benefit of OSPF speed and versatility without the restrictions
on topology.
Basic OSPF configuration steps for each interface are:
1 Enable OSPF.
2 Define an OSPF area.
3 Define interface type.
4 Define interface metrics.
Other parameters may need to be changed.
Advantages of OSPF
OSPF is link state technology as opposed to the distance vector technology and
OSPF addresses the requirements of large scalable networks. Issues addressed
by OSPF are:
• Speed of convergence With OSPF convergence is quicker because routing
changes are flooded throughout the network and new routing tables
computed in parallel.
• Variable length subnet masks OSPF supports variable subnet masking
and advertises varying levels of subnets.
• Route summarization OSPF supports route summarization which is the
consolidation of multiple routes into one single advertisement. It requires
a hierarchical network but has the advantage of confining topology
changes to within an area
and so significantly reduces the workload on
routers in other areas.
Area 1
Area 3
Area4
Area 2
Area 6
virtual route
AUTONOMOUS SYSTEM (AU)
Area 0
(Backbone)