Loop prevention issue in network switch

In layer 2 network environment especially in big network that running in spanning tree protocol, loop will always occurred.  When loop happen network will become congest and every user will be affected. Unless the network run in layer 3 environment than loop will only affect that switch only.

The issue is looping always happen in 3rd party unmanaged mini-switch. Refer to diagram below for a better understand.

When loop occurred in our network it will always hits up to the core switch. as per our core switch we are using Cisco 6513 and for access switch Cisco 2950-2970 and Cisco 6503 CATOS. The weakness of Cisco switch is they fail to block the port that cause a loop. What they advice us to do is to enable bpdu guard. But the problem with bpdu guard is when we enable that feature, all the port for user that using  unmanaged switch will be error disable. 

According to CISCO -  The STP PortFast BPDU guard enhancement allows network designers to enforce the STP domain borders and keep the active topology predictable. The devices behind the ports that have STP PortFast enabled are not able to influence the STP topology. At the reception of BPDUs, the BPDU guard operation disables the port that has PortFast configured.

  In reality when you enable this feature the port only block the direct loop but not loop that occurred in other unmanaged switch. Even Cisco Nexus can't block the loop that occurred in third party switch that connected to Cisco NEXUS!

The weird thing is Extremenetworks switch can prevent loop even the loop is not directly happen in extremenetworks switch. That is really impressing us... I will continue writing about this later...see you ;p