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

[Bart Silverstrim]

Guillaume wrote:

> Hi,
> 
> What I can tell you is:
> 
>  From example, let say the vlan for the phone is 10 abd the vlan for the 
> computer is 5
> 
> On a port used for a phone, you set both vlans on one port so you have 
> vlan 5 and 10. you setup the switch to use the vlan of the computer (5) 
> as the default vlan.
> 
> On the phone, you setup to tell it the phone vlan is 10.
> 
> On the computer, you don't change anything so it will use the default vlan.
> 
> So if you connect a phone to this port, it will use its setup vlan (10) 
> and forward on its second port both vlan and the vlan 5 as default so 
> the computer will use vlan 5.
> 
> If you connect a computer to this port, it will directly use the default 
> vlan (5) which the vlan for the computer.
> 
> I think you have a setup something like that.

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?

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 :-)

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.