This question has been in my mind for a while: is there a reason why you may want to deploy multiple Tier 1 routers?
The answer never crossed my mind and am curious what people here have to say about it, and why you would use multiple Tier 1 routers.
assuming you have T0 and T1 many of them the T0 gateways will be like you ISP CPE and the T1 like the tenant router, T1 is only for having the ability to provide services and tenancy between many networks connected, another reason is that if. you lost all the T0 the networks attached to T1 won't be affected at all to communicated between them.
So T1 "can't " be directly connected to physical networks unless you have the NLB T1 stand-alone case.
I hope this helps.