Not quite a CCNA question but nonetheless:

Sartan

I've recently been given access to a 3com Superstack II switch, 3900 series.

I'm currently trying to trunk it with 802.1Q and a cisco 1900.

They dont trunk!!! Damned things.. they work together as a switch fine, though. I have my vlans set up correctly too I beleive

Sartan

I researched it a little.. i was assuming that the 1900 would default to 802.1Q.. apparently it only supports ISL.. The 3com switch only supports 802.1Q. That's too bad.

Webmaster

Isn't 802.1Q supported in the enterprise version of a 1900?

Sartan

To my understanding it's available with an expansion module. (IE: slot)

http://www.cisco.com/en/US/tech/tk389/tk390/technologies_configuration_example09186a0080143c38.shtml

Background Theory
The Catalyst 1900 runs two versions of images, namely the Standard and Enterprise editions. Trunking is only supported on the Enterprise images, and it only supports ISL encapsulation and does not support 802.1q. This limits the capability of the Catalyst 1900 to form a trunk with other Catalyst switches that can support ISL trunking. Furthermore, trunking can only be configured on the two x 100 Mbps uplink ports on the Catalyst 1900. These are the last two ports on the switch normally marked Ax and Bx. You can configure up to 1005 VLANs on the Catalyst 1900 Enterprise image. The Command Line Interface (CLI) (similar to the Cisco IOS® CLI) is only available on the Enterprise image of the Catalyst 1900.

Note: Catalyst 4000 series switches, with Supervisor I and II, and Catalyst 2950 series switches do not support ISL trunking and cannot be connected to the Catalyst 1900. Catalyst 5500 switches support ISL on certain modules. Issue the show port capabilities <mod/port> command to find out whether a specific module or port supports ISL trunking.