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New Member

Cluster Problems 3550

I replaced one Cat5000 with three Cat3550. The clusterlink is done with the gigastack Cable. If I connect two switches together the link is 1GB/fullduplex, the trunk ist working correctly.

If I connect three Switches together (master, member1, member2) the link ist 1GB halfduplex. My problem now is: after connecting the third switch, the trunk on the gigastack link dissapears after 30-60 seconds. Software on the switch 12.1.(12c)


Re: Cluster Problems 3550


I'm afraid it's impossible to configure trunk while connecting switches in the stack using both ports of GigaStack GBIC.

Cisco GigaStack GBIC data sheet (


"GigaStack GBIC will create a half-duplex repeater bus external to the switch fabric of connected switches. This means that traffic bound from one switch to another will not traverse the switch fabric of intermediate switches."

But trunk configuration requires point-to-point connection. So you can configure trunks in your stack only while using just one port on each Gigastack GBIC.



New Member

Re: Cluster Problems 3550

Thank you for this interesting response.

So if we stack more than 2 equipment together (with GigaStack GBIC) we loose the benefit of different VLANS?

If I take 'normal'GBIC and Fibercable to stack them together the trunk works properly and i can use all the VLANs. But, what is the gain of the Gigastack GBIC?


Re: Cluster Problems 3550

The only gain is if 2 Gigastack GBIC's cost less than 1 SX GBIC. Putting 2 Gigastack GBIC's in one switch and only using one port from each, gives a full duplex connection again.