Cisco VOIP Phone on its own VLAN using DHCP

Hi,

I'm just setting up a new network and have been given the task of setting up some Cisco SPA525G phones, what i want to achieve is to get the Phones to pick up an IP address from a Windows DHCP server, I've created a scope for the Data and a scope for voice.

I believe i need to set some DHCP options so the phone knows where to pick up the IP address from, i'm a little suck here so if anybody could help?

The phones will be daisy chaining with the PC's so will share a network port.

Thanks in advance.
afflik1923Asked:
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LibipappachenCommented:
Hi,

To be able to use your current DHCP server to assign addresses for both VLANs, you must have a Layer 3 (L3) device in the network that can do do the inter-VLAN routing.


To allow the current DHCP server in data VLAN xx to be used to assign IP addresses to the telephones, follow these steps:

Assign a valid address in each VLAN.

Issue the ip helper-address command on the VLAN interface that is connected to voice VLAN yy.

This allows DHCP broadcast packets received on the interface to be sent as unicast packets to the DHCP server in data VLAN xx.

For example config. please read the following link doc.

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080114aee.shtml

BR,
Libi
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afflik1923Author Commented:
We've got a layer 3 switch, the part i am stuck on his how does the DHCP server know which scope to issue the IP address from?
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LibipappachenCommented:
Hi,

    You have to configure an interface VLANs for data and voice with the IP addresses that will be the gateway for that subnet.

Example:


Vlan 100 for data and the subnet is 192.168.1.0/24

Vlan 200 for voice and the subnet is 192.168.2.0/24


DHCP server in data vlan and the ip address is 192.168.1.5

You can configure the IP pool for data is something like 192.168.1.10 - 192.168.1.200

And IP pool for voice is 192.168.2.10 - 192.168.2.200.

In L3 switch the configuration will be something like.

Interface vlan 100
ip address 192.168.1.1 255.255.255.0

Interface vlan 200
ip address 192.168.2.1 255.255.255.0
ip helper-address 192.168.1.5


This ip helper-address configuration will allows DHCP broadcast packets received on the voice vlan interface to be sent as unicast packets to the DHCP server in data VLAN 100.

In these unicast packets the source IP address will be the voice vlan ip address (192.168.2.1) and that will be the gateway for that subnet and destination IP will be the DHCP server IP (192.168.1.5), so as this is a unicast request DHCP server will recognize the source of this packet and will allocate voice vlan pool ip address.
Hope this will help.
BR,
Libi
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José MéndezCommented:
If it is a Cisco switch, the IP Helper address is used. This means that the l3 switch will source a DHCP request in unicast mode on behalf of a phone for example, not broadcast, so the DHCP server will receive the request from an IP address that belongs to the voice VLAN, and that is how it know from which scope to allocate an address.
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afflik1923Author Commented:
Thanks all so far, this makes things clearer, Will i need a second NIC on the windows server for the second scope for the VOIP?
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José MéndezCommented:
No that is not necessary. The same NIC will get requests from different source address without needed a second NIC.
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LibipappachenCommented:
Thanks
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