DHCP adressing for IP Phones

[Alejandro Cadarso Cerdeirina]

Hello

I'm planning a Cisco IP Telephony network and in the document Designing the IP Telephony Network

http://www.cisco.com/univercd/cc/td/doc/product/voice/ip_tele/solution/4_design.htm#xtocid250611

In section IP Addressing says

>Once you configure the speed and duplex settings for >the IP phone, you need to consider IP addressing. >There are three phone IP addressing options:

>

> * Create a new subnet and use that for IP phones >in a different IP address space (registered or RFC >1918 address space).

>

> * Provide an IP address in the same subnet as the >existing data device (PC or workstation).

>

> * Start a new subnet in the in the existing IP >address space (may require you to re-create the >entire IP addressing plan for the organization).

>

>You can implement all of these options using either >DHCP or static configuration

I know that Cisco recommendation is using dynamic addressing for IP phones (I agree with this) and is the default configuration. Although in the Document Implementing the IP Telephony Network

http://www.cisco.com/univercd/cc/td/doc/product/voice/ip_tele/solution/5_implem.htm

Says that:

"DHCP addressing for daisy-chained PCs--A PC or workstation that is connected to the IP Phone

obtains its IP address from the same address pool (subnet) as the phone if DHCP is used for

addressing."

With this I understand that if I have PC's connected to the phone switch I can't use DHCP servers. Anybody knows some workaround?, or at least can I have my PCs with static adressisng and the phones with dinamic of other subnet?

Regards

Alejandro

[SEAN NILSEN]

You can use DHCP for both Phone and PC, even if the PC is connected to the switch port on the phone. If both are in the same VLAN then you only need to configure one scope. If you want PC's and Phones in separate VLAN's, on your switch you need to configure AUX VLAN for the PC and Native VLAN for the Phone. Then setup one scope for each VLAN. Do not use superscopes though as there are known bugs when using AUX VLAN's and Superscopes on Win2k DHCP servers.

[DAVID SCOTT]

We Currently have PC's daisy chained off of our 7960 phones. The PC's get their IP from one DHCP server while the phones get their IP from a different DHCP server. The trick is you need a switch that supports auxillary VLANs. I know the 6500's do and I believe the 4000's do also, although not sure.

[Alejandro Cadarso Cerdeirina]

Thanks,

I wasn't able to find information about this feature, now I think I understand how it works.

[rlyons]

Hello Alejandro,

If you set Auxiliary VLAN’s on the switch the phone and switch will set this VLAN as the voice VLAN (VVID) and send 802.1q tagged frames to the switch for voice. PC’s attached to the phone will send untagged Ethernet frames (unless you have a very unusual PC). The 802.1q frame will specify the Aux VLAN for the voice frames and the switch will assume that untagged frames from the PC are on the normal port-VLAN.

Bob

[i.fouraki]

hi,

when you have a PC connected to an IP Phone you can have different IP subnets for PCs and IP Phones. You configure the port to the switch to which you connect the IP Phone as a trunk, which will have as native VLAN the VLAN of the PCs and as voice VLAN the VLAN of the IP Phones. So you can have static IP addressing for your PCs and your IP Phones obtaining their IP address from a DHCP server.

[dconstantino]

I think because of the 802.1Q you want to use native vlan1 for PC/data and use a aux vlan for voice less config time.