(OT) vlans and cisco switches and dhcp to my system

[Guillaume]

> 
> So the port on the switch has both VLANs "attached" to it, and must be 
> the phone is getting something from Callmanager system telling the phone 
> to subscribe to VLAN X, while by default VLAN Y would be handed to 
> anything else?
> 
Yes VLAN Y would be handed by any device which is not vlan aware so it 
use the vlan setup as default vlan.

> Okay.  I always thought that for security you would set up VLANs to be 
> port specific, not leaving to the client to be able to hop to whichever 
> network it wants.  Apparently Cisco routers even allow that to be more 
> complicated :-)
> 
If the port is setup as "tagged" or "trunk" vlan can not communicate 
between them even if the are on the same port !

But if you attached a device which is vlan aware, you can choose the 
vlan you want !

> This still doesn't explain why the switch was giving the computer the 
> wrong address in our situation (plugging the computer in to another drop 
> going to a different switch would give the right address), but probably 
> someone changed something with the switch without telling me about it? 
> Or perhaps the switch needs to be restarted because something went wonky.
> 

Something has probably been change without telling to you.... that's the 
most possible thing.