How to plug a Cisco 2970 into a Cisco 3550

[burhanloqueman]

Seems obvious? Well we had loops caused by a wrong connection that caused hang ups on two of our core 3550 switches when we tried to plug in two new 2970s via fibre cables.

Anyway, that problem is over - we plugged the 2970s into some 3COM Corebuilder 3500, and I set the port vlan trunking mode to 802.1q mode - and the 3coms are plugged into the 3550.

what port setting should I use on the 3550 and the 2970 (not trunks defined on those ports) if I want these divces to work properly? I had thought to set the 2970s and the 3550 'trunk desirable'.

Should I take down the ports first, set the trunking/vlan mode to 'trunk desirable' and then do the physcial plugging in before bringing the ports up on the Cisco 3550 one at a time?

I am new to this, and I think that spanning tree is causing issues...

[gmarogi]

I think the defaults setting is 'dynamic desirable' which should not be creating any problem if spanning tree is enabled on the vlans carried over the trunk. If you don't want to use trunking, you could set it to access mode by using the 'switchport mode access' command under the interfaces, and make them part of the same vlan.