DHCP and the VLAN

We have two sites, one central site with a CISCO call manager, and a DHCP server. One remote site with users and Cisco phones. The phones are on a VLAN seperate to the DATA network at the remote sites.

I know all bout DHCP helpers etc. However my question is this:-

If the PC gets it IP from the Router via DHCP, how does the phone "know" to go down the link to the head office to contact the DHCP server there an not use the DHCP from the router?

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If the networks are separated by VLANs. Isn't it possible to configure the router only to service the PC VLAN with DHCP? For the other phone-VLAN you can configure the DHCP helper to point to the central server then...

Best regards
if you are using a router, then you would have sub-interfaces defined for the voice and data vlans. you would configure the dhcp scope in the router to match the data subnet and you would configure ip helper under the voice subinterface.

if you are using a switch, then you will most likely have two "interface vlanxxx" configured. beyond that, same as above - local scope matches the subnet and the other vlan has ip helper.

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