RAHUL55 wrote: Actually both the core switches are independant swtches there is no stacking between the core switches and there is no logical configuration also.
You initially wrote "i have 10 edge switches of HP 2610 and 2 core switches of brocade 6610f for redundancy and a routing switch of hp 6200 yl" so, as I understood it, your two Brocade ICX6610-24F switches placed at core are necessarily interconnected in some way (maybe they are not directly interconnected together but for sure they are indirectly through edge and through the upstream HP 6200 yl switch) and they necessarily have a configuration that provide that redudancy protection...otherwise in which way they provide the redudancy you're claiming for? Is it possible that you have VRRP configured at core level and your two Brocade switches, acting as real core ones, are configured to provide Layer 3 functionalities to downstream devices (edge switches)?
Difficult to say what is happening (apart ascertain that probably a mechanism like STP is intervening because a Loop between your edge and your core was detected when you link those layers with a second uplink per each edge Swtich) if you are telling us there is nothing more than that you already described about your scenario: IMHO your description of your network topology is far to be complete or, if it is really as you wrote, there isn't redudancy at core level...or, more, what you call "core" isn't acting as the "core".
I can't help more far of that point...sorry.