We are having two 4900M serise switches as the distribution switches in the network connecetd to 6500 VSS core switch. We were getting OSPF & HSRP flap every 3 hours, after trobleshooting it fund that every time TCN comes from different access switches pointing towards the distribution switch1. So suspected issue in the distributon switch 1 which was root bridge,hence we made distribution switch2 as a root bridge and not observed any flap in network for more than 48hours. Now again we have made disribution switch1 as the root bridge but not observed any flap in the network from last 17hours. So what can be the issue here?