problem in network

Hello
I have a problem in network , maybe you can help me with this. I present Broad Band service and the structure is like this: There are three network cards in my access server(mikrotik), one is Public IP and the other Local IP. I have done a NAT in access server(mikrotik).On the Local access server i set the IP 192.168.11.10. The user connects to IP through VPN and then can go to the network and use the internet. Up to here every ting is Ok but sometimes in this local network we have a problem; suddenly the users who have connected to the IP 192.168.11.10 by VPN, become disconnected and for about 40 seconds in Local network, it is impossible to ping the IP 192.168.11.10.
Once, before the above happens i put a ping in Local network to IP 192.168.11.10. Ping was on 1ms (which is a completely normal ping) but immediately when the problem happened i saw that the ping 192.168.11.10 suddenly became “time out” (for 40 seconds) and then the ping of this IP appears and not on 1ms but 10 ms,7,9,6,5,8… It shows these numbers and it seems that the IP 192.168.11.10 have been fixed on some other place. (but that is not possible because nobody can reuse an IP which is busy because he/she will receive “IP Conflicted”) and then after seconds ping returns to its normal position and becomes 1ms.1ms.1ms… again. I use switch 2960 in Local network and I have put VLAN adjustments in this switch. Probably (maybe 85%) I think a Broadcast storm happens in network and a Broadcast causes this loop in network.
Is there any friend who knows how to solve this problem? Let me tell you that in this network i use 8 normal switches and sometimes when there is a disconnection with Micro tic, it takes a long time that there is no connection(about 4 minutes), then this is solved by turning off one of the switch hubs (which is randomly chosen). The switch 2960 in this network is the main switch which means that all the normal hubs are connected to the switch 2960.

plz help me
tks

Can any one guide to solve the problem :frowning: