Segment Shuts Down When Switch Plugged In

[nkillgore]

I'll start off with a description of the existing topology.

WAN link plugs into a 2821 Router with an switch module in it. About 8 clients are plugged in to the 2821.

2821 connects to super cheap netgear switch (I'm 99% sure it's stripping dot1q headers) via one of the ports in the switch module. About 4 people are connected to the netgear.

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Now, I sent a catalyst 3560g to the branch because they wanted to extend into a new building. Someone decided to run a single cable from the netgear to the 3560. On the 3560, I have about 5 clients and a couple of APs.

So it goes  2821 -> Netgear -> 3560. All of these are single connections.

When the 3560 gets plugged in, all clients on the netgear lose their connection, and nothing on the 3560 works. It happens almost instantly.

I can't figure out why connections are dropping. Any ideas?

The APs have about 4 VLANs onn them, and the PCs are on their own VLAN (the native VLAN).

[paul driver]

Hello
When tou sent the 3560 to site was it pre configured?

thinking:
1) stp
2) ip routing enabled
3) duplicate addressing

would be nice to see config of the cisco devices

res
paul


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[nkillgore]

The config on the 2821 is pretty massive. The 3560 should have been configured before it went out. Is there something specifically that you are looking for?

Is it possible for there to be a switching loop even though there is only one cable between each switch?


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[nkillgore]

There was a native vlan mismatch.