Low traffic overhead. OSPF is economical of network bandwidth on links between routers.
Fast convergence. OSPF routers flood updates to changes in the network around the internet, so that all routers quickly agree on the new topology after a failure.
Larger network metrics. This allows a network planner the freedom to assign costs for each path around the network, to give fine control over routing paths.
Area based topology. Large OSPF networks are organised as a set of areas linked by a backbone. Routing within each area is isolated to minimise cross area discovery traffic.
Route summaries. OSPF can minimise the routes propagated across an area boundary by collapsing several related Sub-net routes into one. This reduces routing table sizes, and increases the practical size of a network.
Support for complex address structures. OSPF allows variable size sub-netting within a network number, and sub-nets of a network number to be physically disconnected. This reduces waste of address space, and makes changing a network incrementally much easier.
Authentication. OSPF supports the use of passwords for dynamic discovery traffic, and checks that paths are operational in both directions. The main use for this is to prevent misconfigured routers from "poisoning" the routing tables throughout the internet. In practise this is not a serious problem, as almost all end user devices do not support OSPF.
Memory overhead. OSPF uses a link state database to keep track of all routers and networks within each attached area. With a complex topology, this database can be much larger than the corresponding routing pool, and may limit the maximum size of an area.
Processor overhead. During steady state operation the OSPF CPU usage is low, mainly due to the traffic between routers. However, when a topology change is detected, there is a large amount of processing required to support flooding of changes, and recalculation of the routing table.
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