VLAN & DHCP configuration

[disturbedone]

Hi, this may be a dumb question but needs asking. It seems like a relatively straight forward scenario but am looking for advice/suggestions/answers on it.

Small-Medium Business customers (size varies) but being SMB cost is a factor. Single DHCP server (eg W2K3) with single NIC, Cisco ESW-500 switch supporting CDP, IP phones (could be Polycom, Cisco or other) that support CDP.

Requirement: split data & voice onto separate VLANs to separate broadcast traffic from voice on LAN.

CDP will assign automatic VLAN to phones on boot before DHCP.

The question: is it possible to have a single scope providing DHCP to data & voice clients in separate VLANs?

Yes, a more complicated solution such as multiple NICs in DHCP server each on a separate VLAN switch port or using an eg Cisco router that is VLAN aware would do this but being SMB cost is a factor.

Maybe the answer is no. That's fine. But if yes then advice on the solution would be appreciated. To me it doesn't sound like that much to ask.

 

[VinceWhirlwind]

The Data and Voice each have their own subnet.

Each subnet is configured as a scope in the DHCP server, so you have two scopes.

The DHCP server exists on, say, the Data subnet, and the inter-VLAN router is configured to forward DHCP requests from the Voice subnet to the DHCP server using configuration that is called "IP-helper".

 

[mattKnight]

The Data and Voice each have their own subnet. Each subnet is configured as a scope in the DHCP server, so you have two scopes. The DHCP server exists on, say, the Data subnet, and the inter-VLAN router is configured to forward DHCP requests from the Voice subnet to the DHCP server using configuration that is called "IP-helper".

I'd agree with that, but it does make the assumption that the customer's infrastructure supports intervlan routing (either by an external router or layer 3 switch)

In my experience - as a PABX installer (initially trained by disturbedone :-0) many SMB customers don't know what a VLAN is or neccessarily why they are a good idea to implement. They often have layer 2 managed switches - with no programming on them (soem totally default) and don't want the overhead of an inter-vlan router that they don't understand and that their IT company are incapable of supporting.

One solution I have used in the past is a freeware DHCP server called (google dualserver) which is fully featured but will run on a basic workstation. Not ideal for many reasons, but often enough!

Take Care

Matt
I have always wished that my computer would be as easy to use as my telephone.
My wish has come true. I no longer know how to use my telephone.

 

[VinceWhirlwind]

The original message had this in it:

"Requirement: split data & voice onto separate VLANs to separate broadcast traffic from voice on LAN. "

My solution to the customer who only has a layer-2 device in their office is to ask their WAN provider to provide inter-VLAN routing via subinterfaces with a dot1q trunk from the on-site router.

If you document your installation properly, any monkey can support it.

 

[mattKnight]

>WAN provider to provide inter-VLAN routing via subinterfaces with a dot1q trunk from the on-site router.

That is a neat solution - it evidently works for you. However in the market place I was in, most external connectivity is DSL (with WAN links being Tunnels across internet) using cheap and nasty routers (often the free ones provided by the ISP) which don't support sub-interfaces.

And some of the support monkeys I've had to deal with woudl have difficulty opening the documentation folder...

Take Care

Matt
I have always wished that my computer would be as easy to use as my telephone.
My wish has come true. I no longer know how to use my telephone.