I have a basic question about routers convergence times.
In campus networks, We know that it is better to go for a layer3 backbone instead of a layer2 backbone for one of the major reasons of delay in STP stabilization times which the routing protocols' convergence times can achieve.
Now to my basic question ..
Time for a normal 802.1D STP to converge is, lets say 45 to 50 seconds. (20 maxage + 30 Fwd_Delay)
Lets consider OSPF with a hello time of 10 s and deal interval of 40 s.
This means that a router B (connected to Router A) will only bounce the neighbourship with A and purge the routes learnt from A only after 40 secs of not hearing any hellos from A and run SPF again.. So it can't be that way, can it ? What basic idea have I not understood here ?
Thank you !