I have the following topology. The notebook computer has to access the internet.
In what case should R3 (as the core router & default gateway for the internal network) having iBPG configured or having routes redistributed via OSPF to it?
Or if there are any better solutions?
First, does R3 support BGP and does it have enough RAM to support all the routes on R1 and R2? If not, then BGP isn't an option.
Second, do R1 and R2 receive a full Internet routing table? If so, then redistributing several 100k routes into OSPF would not be wise if at all possible. In this case I'd recommend using iBGP. On the other hand, if R1 and R2 are only receiving default routes, or a small number of routes, then redistributing into OSPF would be the preferred option and would allow the routing information to reach other OSPF only routers in the internal network so that they can make more informed routing decisions.
If R1 and R2 holds full internet routing table answer is never. Only default route should redistributed towards OSPF in some occasions maybe you would need to redistribute certain prefixes into OSPF but you need to have a good reason for that. You need to remember that every time a network is deleted or added, an SPF recalculation happen. Dijkstra's algorithm requires lot CPU resources. Routes on internet are flapping, appear and disappear. With this number of routes your router would be doing continuously recalculation which would taken all CPU time.
