Simple DHCP Voice and Data question

[Rick Morris]

I am drawing a complete mind blank on this and was hoping for a simple answer or a link.

I have set up 2 DHCP pools on my Cisco 3750.  One is for Data and the other if for Voice.

(before anyone wants to shake their head in shame please understand I do not like Nortel and want everything Cisco - ok I feel better now)

I have Nortel switches at my access layer, (again please do not shun me!!!).

I have created an LACP trunk to allow multiple VLAN's across my network.

My question is, even in the Cisco world where I still have some Cisco as access, how does the interface know where to send the DHCP request?

For example:

I have vlan 100 for data and 200 for voice

on the interface I have configured:

interface GigabitEthernet1/0/1

switchport access vlan 100

switchport mode access

switchport voice vlan 200

spanning-tree portfast

end

If I plug in a phone how does the phone know to use the DHCP pool for voice?

ip dhcp pool DHCP-NETWORK

   network 10.1.1.0 255.255.255.0

   domain-name xxxxxxx.net

   dns-server 10.1.1.96 10.1.1.97

   default-router 10.1.1.254

!

ip dhcp pool VOIP-NETWORK

   network 10.100.100.0 255.255.255.0

   domain-name xxxxxxx.net

   dns-server 10.1.1.96 10.1.1.97

   default-router 10.100.100.1

   lease 30

!

interface Vlan100

description Data VLAN

ip address 10.1.1.254 255.255.255.0

!

interface Vlan200

description Voice VLAN

ip address 10.100.100.1 255.255.255.0

!

[barry]

Hi Rick

In a pure Cisco world, the phones and switches use CDP. The switch tells the phone (via CDP) that its voice VLAN is 200. The access VLAN is 100. Packets to / from the phones PC switch port are placed in this VLAN.

The traffic to / from the phone itself is therefore automatically tagged in VLAN 200, and therefore matches the correct DHCP scope.

Obviously in a Nortel switch environment which doesn't support CDP, you need to do things differently.

HTH. Barry

[Gordon Ross]

LLDP might be your friend here (Don't know if Nortel supports it, but it's less Cisco centric) Just watch out, though, that not all CallManager devices support LLDP. (ATAs don't for one)

Otherwise, you'll have to statically assign the VLAN to all the devices. (Again, not all phones support static VLAN assignment....)

GTG

[Rick Morris]

Yes, I see LLDP config options...haha never actually used it so not too familiar with it.  Guess I get to read a bit more.