A singleton object (GlobalRouteManager) is responsible for populating the static routes on each node, using the public Ipv4 API of that node. It queries each node in the topology for a "globalRouter" interface. If found, it uses the API of that interface to obtain a "link state advertisement (LSA)" for the router. Link State Advertisements are used in OSPF routing, and we follow their formatting.
The GlobalRouteManager populates a link state database with LSAs gathered from the entire topology. Then, for each router in the topology, the GlobalRouteManager executes the OSPF shortest path first (SPF) computation on the database, and populates the routing tables on each node.
The quagga (http://www.quagga.net) OSPF implementation was used as the basis for the routing computation logic. One benefit of following an existing OSPF SPF implementation is that OSPF already has defined link state advertisements for all common types of network links: - point-to-point (serial links) - point-to-multipoint (Frame Relay, ad hoc wireless) - non-broadcast multiple access (ATM) - broadcast (Ethernet) Therefore, we think that enabling these other link types will be more straightforward now that the underlying OSPF SPF framework is in place.
Presently, we can handle IPv4 point-to-point, numbered links, as well as shared broadcast (CSMA) links, and we do not do equal-cost multipath. We also do not allow for non-unit-cost links, although it should be trivially extensible to do so.
The GlobalRouteManager first walks the list of nodes and aggregates a GlobalRouter interface to each one as follows:
typedef std::vector < Ptr<Node> >::iterator Iterator;
for (Iterator i = NodeList::Begin (); i != NodeList::End (); i++)
{
Ptr<Node> node = *i;
Ptr<GlobalRouter> globalRouter = Create<GlobalRouter> (node);
node->AddInterface (globalRouter);
}
This interface is later queried and used to generate a Link State Advertisement for each router, and this link state database is fed into the OSPF shortest path computation logic. The Ipv4 API is finally used to populate the routes themselves.