Question : configuration problem in 3com switches in a mixed 3com and cisco switches environment

When I did a network discovery on a subnet using 3com network supervisor (version 4), a misconfiguration report was generated stating one of the port must enable for spanning tree protocol for a connection with a workstation.

On clicking a link for further information, it stated that there was a 'fast start' problem.

The problem port is unit 3 port 26 on a '3-stacked 3com switches 4226' connnected to a cisco 3550 switch through trunking 802.1q.

Answer : configuration problem in 3com switches in a mixed 3com and cisco switches environment

When you connect a device (PC, Printer, etc) to a Port on a Switch, the Switch goes through a series of steps such as Listening, Learning, Blocking, and Forwarding.  When you adjust the spantree setting to PortFast, you are instructing to Switch to skip some of these steps to increase the speed of connectivity to that port.  However, you need to use care in deciding which ports to enable these changes to prevent a Spanning Tree Loop.  Usually, with PC's and Printers you are safe, but use extra caution when connecting Switches and Routers to these ports.

Another thing to consider, ensure that your ports are hard coded for 100 MB and FULL Duplex as this may cause the problem you described.  On the cisco 3500, type config t to enter Global Configuration Mode, then type interface Fa/## where ## is the port number on the Cisco 3500.  Next type 'spanning-tree portfast' to enable portfast on that port.  On the 3Com Switch, you should be able to enable portfast by clicking on the graphical selections using your browser.

Best of Luck
Steve