Connecting Cisco Catalyst 5500 to network introduces VLAN problems

We bough a Cisco 5500 13-slot switch to connect to our current network existing of a couple of 2950 switches with +/- 10 VLANs. Some of the ports are trunked. When I plugged in the Cisco 5500 all status led ports except the trunk ports on the 2950 switches became orange. This caused network outage.

It turned out the VLANs on the Cisco 2950 switches were removed. The ports where still assigned to a VLAN, but the VLAN did not exist on the switch.

I was wondering if anyone knows what protocol was the cause for this problem and how to disable it. I cannot just try anything, because this is a live setup and we dont have a network lab.


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VTP. Two conditions had to be met, for this to have happened Your new switch might have had a config revision number higher than those on the 2950s. All switches were in server mode.

The switch with the highest configuration revision number will impose its vlan info on all others (or rather the other switches think the new switch has fresh information).

Anyway, to avoid this, on ure 5500 conf t vtp mode transparent

or, if u want ure 550 to learn vlans from the 2950,

vtp mode client

power cycle the 5500. & do show vtp status .

ensure the config revision is zero before pluggin in

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Thanks very much :) It seems to be VTP indeed, all switches are now aware of the VTP domain that was only configured on the 5500. We have set every switch to transparent mode and configured a VTP password just to be sure :)

Will try if it works :)

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