2970 Switch Connect to an Unmanaged One

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Dec 13th, 2007
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I have multiple 2970 switches and 2 4506 switches that all have STP enabled.

I have connected one of the 2970 switches to an unmanaged switch ( 3com ), i am afraid that this would cuz a loop in my network !

is there anything that can be done on the 2970 switch to avoid a loop ?

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Edison Ortiz Thu, 12/13/2007 - 07:05
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Just have one link from the 3Com connected to a switch. Attempting to connect more than one link from the 3Com to any Cisco gear will produce a network loop.

majdalani Thu, 12/13/2007 - 23:45
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i will be using 2 ports from the 3com switch.

one port from 3 com switch to a port in cisco switch that has the vlanx.

the other port from the 3com switch will be going to another port on the cisco switch with vlany.

would this creat a loop ?

smothuku Fri, 12/14/2007 - 02:02
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Hi ,

Better connecte ports which are in the same vlan to 3 com switch.If you connect more ports which are present in different vlan's may casue more broadcasts and network loop.

Sometimes network may be screwed because of unwanted loops because of 3 com.



majdalani Fri, 12/14/2007 - 02:53
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Hi ,

iam recieving this warning : CDP-4-NATIVE_VLAN_MISMATCH

i have read that this can be stopped using the command : no cdp run

the issue with me is that i need few machines to use both vlans. but i do not change my access list on the 4506 switch.

so i configure these computers with 2 IPs, one for vlanx and the other for vlany.

now these computers are then connected to the unmanaged switch ( 3com ) , then from the 3com i have one port connected to a 3750 switch which have vlanx configure on it, and the other port comming from the 3com is connected to the 2nd port in the 3750 which has vlany configure on it.

i hope its clear now.


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