I solved the problem on my own and I want to share the solution.
We have two terminal server with NLB on esxi host.
With default configuration all packets are sent broadcast to all ports of your switch. (in my company, network overloads caused a lot of blocks in our warehouse management software)
As recommended by vmware, I activated the multicast with igmp, but the switch doesn't memorize mac address of the physical network card of the server and packets was still in broadcast.
The solution is to activate IGMP on the vlan where the server is connected, because in default configuration the switch can't correctly recognize the protocol of the packets.
