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

[Bart Silverstrim]

Off topic question but network related, and I think there's people here 
that have expertise in this field that could clarify this for me.

I'm a tech that normally works on OS and system related problems, so 
Cisco switches aren't my forte.  We have a Cisco inline powered switch 
that is set up, according to my boss, "for VLANs and QOS, etc..."

That switch is running to offices for Cisco IP phones, which get 
addresses on a 192.168.10.x range via DHCP to the Callmanager system 
from Cisco.  Some of the phones have a switchport on the back into which 
a computer can be plugged in (so one drop to the desk can support 2 
network devices).  The computers were getting an address in the 
192.168.0.x range, again via DHCP.

We had a call about a computer that wasn't going through the gateway to 
the Internet.  The computer was plugged into a wall drop that in turn 
ran into the inline-power switch meant for the phones rather than a 
second non-powered switch that is usually used for drops that aren't 
using the phones, and the computer was getting an address in the 
192.168.10.x range as if it were a phone.

I asked, if you can plug a computer into a phone that then goes to the 
powered switch, how is the computer getting the "proper" address, while 
if the computer were plugged directly into the drop, it was getting the 
wrong address?  Wouldn't the computer getting an address from the 
phone's port in turn have to pass through that same inline-powered switch?

The response I got was that the phones are on a separate VLAN.  I never 
had an answer about how the switch would differentiate the computer 
passing through the phone rather than directly into the drop.

Anyone willing to try giving a summary of what had happened, what I'm 
missing here?  I was just repeatedly told that the phones are on a 
separate VLAN despite the proper address being "passed through" to the 
computer when the computer was connected to the phone.  I thought VLANs 
were port-specific on the switch.