Than you

But the problem is : each stack is connected to tow cat 6500( standby switches) with uplink gigabit fibre, i won't the stack cascade to influate the uplink.

what i have now is : the link over gigastack is Bloced and the tow switch communicate over uplink

You need to configure the GigaStack links as trunks, otherwise only VLAN1 will have full connectivity to both 6500s.

One of the GigaStack ports will block because Spanning Tree protocol determines that there would be a loop without a blocking port. No doubt your network is configured so that the one of the two core 6500 switches is the root switch. Your GigaStack link is therefore the remotest part of the network from the root switch, so one of its ends will block. This behaviour is proper and normal.

If you changed the Spanning Tree topology so that one of the two uplinks to the core blocked, instead of the GigaStack, you would have 1Gb/s bandwidth instead of 2Gb/s from the stack to the core. Is this what you want?

Hi

the tow cat 6500 work one as stondby of the other so to tow uplink must be one backup of the other.

what i want is that the stack act as one switch and the one uplink active to the active cat6500 switch and when this iplink or the active 6500 down the second 6500 take over and became the master with the second uplink