VLANS and DHCP

July 8, 2009 at 11:12:08
Specs: N/A
I have a small network of about 50 users and 50 other network devices.
We are adding a voip phone system with about 50 phones and poe switches to support them.
I want separate out my servers, workstations and phones onto different networks.
I plan to configure two new v-lans : one for pc's and one for a voice network. The remaining
devices will continue to reside on the existing network.
I will configure each port on the new switches to be tagged for both v-lans.
When I connect a phone, I want it to aquire and IP address from my dhcp server in one scope
and when I connect a pc , I want it to acquire and IP address and dns servers from another scope. How do I get that to happen?

Can anyone help on this one?


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#1
July 8, 2009 at 11:18:44
ask yourself how dhcp is going to differenciate between the two devices [phone vs wkst]?

Solution is you can't do both on a port. You must set one port to phones vlan and one port to pcs vlan.


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#2
July 8, 2009 at 12:03:32
Ok, first some basic how-to for VLAN tagging.

Every managed, VLAN capable switch I've worked with has VLAN 1 as the default VLAN. In most cases, it's standard procedure to use VLAN 1 as your management VLAN. This will be the VLAN (subnet) on which all network appliances reside. Which is to say, all switches, routers etc.

If you're just starting out with VLAN tagging, a word to the wise. Have your VLAN tag match the subnet.

example:

VLAN 1 = 192.168.1.0
VLAN 2 = 192.168.2.0
VLAN 3 = 192.168.3.0
VLAN 4 = 192.168.4.0

and so on.

I want separate out my servers, workstations and phones onto different networks.

This will give you 4 VLAN's when you're done. As per my above example:

VLAN 1 = management
VLAN 2 = Server
VLAN 3 = VoIP
VLAN 4 = client

If you have a large number of network printers, it may be worth your while to create a 5th VLAN specifically for them.



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#3
July 8, 2009 at 15:17:10
"I want separate out my servers, workstations and phones onto different networks"

Anyone see a problem with this statement?

If the servers are in one vlan and the workstations in another they will not communicate unless you have a vlan router.

Subnetting on top of vlans is not a requirement for vlans. It is for more granularity in very large organizations.


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Related Solutions

#4
July 8, 2009 at 15:57:43
Hi,

Try this,

Try to configure the switch for dynamic vlans (Mac adds based vlan)

Group all the mac adds of your phone to a particula vlan and mac adds of all the workstations in to another vlan.

Map this vlan to the dhcp server to provide ip adds to its range.

You can use the same port for phone aswellas for the workstation - Depending on the mac adds the switch identifies the device and assigns the vlan.

According to the vlan the device can asquire ip adds.

Regards

L8ians.


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#5
July 8, 2009 at 17:18:28
Good suggestion except we don't know if Mulberry has the switches to support dynamic vlans.

Each vlan would have to have a dhcp server.

But I think this is all for naught since Mulberry have POE switches for the phones.

Appears to me Mulberry you will have to have the ports for phones wired to the POE switches along with the VoIP server. Normally this phone network is a separate network entirely than the wkstation/server network.

You would need to lable the ports accordingly.

But your phone vendor should have discussed this with you in detail before you purchased the system. Doesn't sound like this happened.


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#6
July 9, 2009 at 04:33:28
thanks to all for your responses. I appreciate the input

Ok, first some basic how-to for VLAN tagging.....
VLAN1 has everything in it for now. I want to create VLAN2 for the pc's
and VLAN3 for the phones.

I was hoping that for each user port on the switch, I could tag the port to VLAN1 and
VLAN2 which I believe I can do.

wanderer......ask yourself how dhcp is going to differenciate between the two devices ...
that was exactly my question. Is there really no way to do that on one port?

In my initial discussions with the phone vendor they said that when you set up a phone you can
tell it which vlan you want it to connect to? Is anyone familiar with that feature?

L8ians....Try to configure the switch for dynamic vlans ....

I can associate MAC adds with a vlan! I need to work out how to associate a vlan to a dhcp server.
Is is it possible to associate vlans with different dhcp scopes on a windows dhcp server?


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#7
July 9, 2009 at 07:52:43
What I don't understand is why you would want to double up like this. Do you not have enough network outlets in your offices? Are you running short of available switch ports and can't afford another switch?

You're just adding complexity to your network by doubling up on ports like that. I totally understand if you're constrained by a lack out available network outlets in offices or ports on switches. But, if you have enough of both to support a separate connection for data/VoIP, you really want to go that route.

In my initial discussions with the phone vendor they said that when you set up a phone you can tell it which vlan you want it to connect to? Is anyone familiar with that feature?

Yes. If you think about it, this is an important feature. If you can't tell a VoIP phone which VLAN to use, then you couldn't use it in an environment that employs VLAN tagging.

We VLAN tag extensively (and subnet.....and thanks wanderer for pointing out subnetting is not necessary when VLAN tagging...I keep forgetting it since I work in such a large environment that we do subnet/VLAN) and without the capability to assign a VLAN to the phones, we'd have never got them to work in our environment. So, when we do the initial setup on a VoIP phone, we have to tell it which VLAN it will be using.



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#8
July 9, 2009 at 08:05:12
"Is there really no way to do that on one port?"

Not without dynamic vlan tagging.

If you have the pc vlan and the phone vlan on the same port this would also mean you have two dhcp servers on the same port.

Unless you do dhcp ip reservations [associate a mac with a ip] the device will be serviced by which ever dhcp server responses first.

That is a lot of work to setup and then even more to maintain.


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