This is a loaded question. I've asked several people smarter then I and nobody seems to know for sure. I have one router with 21 subinterfaces on it( not my choice) I wil say this about it, subinterfaces are great BUT!!!! you put all of your eggs in one basket. Whatever impacts one subinterface will surely impact the rest. You also need to be aware of how much oversubscribing you have on the interface as a total. It's possible to kill the interface by forgetting you have a T1 ( 1.54) and adding 5 interfaces each with a CIR of 1.54 You may laugh but I have seen this happen. Any intrusive testing will impact EVERYTHING on the interface.. it's not by frame circuit, it's by physical port. I watched SBC smoke all 17 circuits of mine trying to fix a frame protocol problem. Oops!! One more thing to watch out for is memory. Each subinterface sucks up memory and if you forget on a marginal router, you may get bit.
Mike S
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