Media for Trunk, STP and duplex

Hi,

Obviously, I am missing something very basic.

I want to hook a new switch (3560) to an existing one (2950).

On the existing 2950, I define a port as trunk and I define an encapsulation mode. I define the corresponding port on 3560 with the same parameters.

I get all the VLan on the new switch and everything is fine. I am able to see the trunk port STP status on the 2950 as "forwarding".

Now the point I do not understand : whenever I put one of the 2 ports (on

2950 or 3560 end) in half duplex mode, the port on the 2950 will be force to "Blocking" state.

(And actually, I have troubles to get it back even forcing the ports in full duplex.)

Could explain me the root cause for it ? I feel that I am missing an important point.

Thanks in advance,

A puzzled newbie..