User manual

Network Setup
105
OSPF
Note
This example is adapted from the LARTC (Linux Advanced Routing & Traffic Control)
dynamic routing howto, available from: http://lartc.org/howto/
LARTC is an invaluable resource for those wanting to learn about and take advantage
the advanced routing capabilities of Linux systems.
OSPF stands for Open Shortest Path First, and some of its principal features are:
• Networks are grouped by areas, which are interconnected by a backbone area which
will be designated as area 0. All traffic goes through area 0, and all the routers in
area 0 have routing information about all the other areas.
• Routes are propagated very fast, compared with RIP, for example.
• OSPF uses multicasting instead of broadcasting, so it doesn't flood other hosts with
routing information that may not be of interest for them, thus reducing network
overhead. Also, Internal Routers (those which only have interfaces in one area) don't
have routing information about other areas. Routers with interfaces in more than one
area are called Area Border Routers, and hold topological information about the areas
they are connected to.
• OSPF is based on Dijkstra's Shortest Path First algorithm, which is CPU intensive
compared to other routing algorithms. But really is not that bad, since the Shortest
Path is only calculated for each area, also for small to medium sized networks this
won't be an issue, and you won't even notice.
• OSPF counts with the special characteristics of networks and interfaces, such as
bandwidth, link failures, and monetary cost.
In this example we set up route management using OSPF for the network topology
described by the following diagram.