I couldn't create a routing recursion loop like you managed but I can explain what is happening.
When you redistribute from an IGP into BGP the MED value in BGP is derived from the IGP metric.
If MED is used by the BGP router to choose between multiple routes for the same network the lower the MED value the better.
There are two rules with MED and how it works between BGP peers -
1) If a BGP router learns of a route from a BGP peer it can pass the MED value to any other IBGP peer but not to EBGP peers.
2) if the route was injected locally into BGP and this router has an EBGP peering with another AS it can pass on the MED value
In your scenario when you redistribute OSPF on R1 both R7 and R8 receive the route with the MED value but they cannot advertise that to R9 or R10.
R9 and R10 receive the advertisements without the MED value and advertise them to each other because they are IBGP peers.
So R9 has two BGP routes for the same network, one is AD 20 and one is AD 200.They both have the same metric because the MED value is not passed on.
It also has an EIGRP route which is AD 90.
R9 will pick the EBGP route as the best BGP path and because it has an AD of 20 it is also preferred to the EIGRP route and so is installed in the IP routing table.
When you redistribute on R7 though things change. The MED value is derived from the IGP metric and because R7 is an EBGP peer it can advertise the MED value to R9.
Now R9 has again three routes for the same network. It has an EBGP route with a MED value from R7, an IBGP route without the MED value from R10 and an EIGRP route.
If you do a "sh ip bgp <network>" on R9 you will see the two routes. One will have a metric > 0 which is the route received from R7 with the MED value. The route received from R10 will have the default metric of 0 because the MED value couldn't be passed on because R8 received that IBGP route from R7 and so cannot advertise the MED to R10.
In the BGP best path selection MED has a higher preference than EBGP vs IBGP routes so R9 chooses the IBGP route this time as the BGP best path because it has a better metric. But this route has an AD of 200 and the EIGRP route has an AD of 90 and that is why the EIGRP route is installed into the routing table.
Hope that makes sense.
Jon
