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OSPF stands for Open Shortest Path First. It is an enhancement to RIP and is intended to be more flexible. The OSPF specification is published as (RFC) 1247. OSPF deals with routing inside one Autonomous System (AS) but it can be given information about routes outside of the AS to allow it to intelligently select a gateway. The external routes can be statically entered such as in figure 1 or dynamically taken from an Exterior Gateway Protocol (EGP) such as BGP in figure 2.

Figure 1 shows an imaginary SOWN network where several nodes are connected to ISPs who in turn are connected to each other. OSPF can be configured to route traffic to ISP 1 through router 5 and traffic to ISP 2 via router 6 with all other traffic going via router 3 to ECS and the rest of the Internet. In addition to this configuration OSPF can be told about the link between ISP 1 and ISP 2 and thus route data from router 5 to router 6 via the ISPs should routers 4 and 2 fail. OSPF does not need to know how the ISPs networks work to perform this routing

As an aside: while this sounds nice it would not work with the current SOWN network because ISP 1 and ISP 2 would refuse to route 10.x.x.x addresses through their network. It could however work with IPv6 as it would be possible to get a provider independent /48 subnet for SOWN which could be announced over different ISP links.

Figure 2 shows what the author believes was the intended setup for the Consume network where different free wireless networks are connected to each other via BGP controlled links. In this situation OSPF gets route information from the BGP routers who know routes to different free networks. OSPF will internally route packets across the internal network to the BGP router best positioned to route the data onwards. OSPF will also route transit data across the network between BGP routers.

From what the author understands of OSPF the above information is correct, before the SOWN meeting on the 11th I hope to setup both examples and will post the Quagga/Zebra configuration files here.