Mivoice 400, 69xx SIP phones and DHCP on Fortinet with voice VLAN

[Tinos]

Hi all.
We have MIVO400 SMBC which was working fine with 69xx SIP phones on a network that had PCs and phones on the same subnet. Recently we separated subnets and created a second one for the phones and a voice VLAN.
We are using Cisco switches and configured the voice VLAN on all access switchports. The phones must get DHCP from the SMBC. PCs connect to the back of the phones and get DHCP from Fortinet Firewall. When connected to the network the phones are not getting the voice VLAN ID and fail to get IP addresses (If I test with a phone on MINET it gets the voice VLAN ID). They get stuck on "20% DHCP: Waiting for IP". What configuration must I do on the Fortinet to enable the phones to get the voice VLAN ID and make the request DHCP from SMBC?
Please advise.

 

[Lundah]

Use the "ip helper-address" command to set the helper address on the Voice VLAN to be the SMBC, then the DHCP requests from the phones should be relayed to the controller.

 

[Tinos]

The SMBC is already on the same voice VLAN with the phones. The phones bootup in the PCs default VLAN. An ip-helper on the PCs VLAN will also affect the PCs DHCP.I need some DHCP option that makes the phones to know their voice VLAN.

 

[TCSI17]

You can set the DHCP Option 125 on the default VLAN with the magic Mitel string to give the phones the VLAN and the config server. This is only handed out to the Mitel phones that request option 125.
You will need to generate this magic string though using the Mitel DHCP application (separate app downloadable via Mitel's software download site). This application spits out the string in hex which you can then put in the Fortigate.