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

Posted on 2004-09-11
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Last Modified: 2008-01-09
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.
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Question by:thtan56
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SteveDavis earned 500 total points
ID: 12036481
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
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Author Comment

by:thtan56
ID: 12055322
unit 3 port 26 is a port on the stack of 3com switches (3 stacked together).
I don't think any change is needed on the cisco as the problem pointed to 3com switches.

At one stage, I disconnected the cable on that port where a pc running windows os.
However the same misconfiguration report was regenerate.

I tried Steve's suggestion by enabling the port using the brower.
I tried the network discovery and the same report was generated.
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