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Not enough IP Addresses for VOIP Install

We are having a VOIP phone system installed in the next month.  We won't have a enough IP addresses with our current class c private address to provide ip addresses to all of the new phones.  Current IP scheme: 192.168.2.0   255.255.255.0.  

According to our vendor we will be VLANing the voice traffic and the phones and computers will share an ethernet connection.  I'm not too familiar on VLANing.  Should I just supernet our whole ip scheme to a /22 network and change all of the subnets on our computers and devices to 255.255.252.0?  What are my other options?  I would like to make whatever changes with the least amount of interruption.  What is the best way to do this?
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Kyle Abrahams

8/22/2022 - Mon
Kyle Abrahams

Can't you just create a different subnet for the phones?  EG: 192.168.2.2 -> 192.168.2.255?

Set default gateway to 192.168.2.1 . . . configure a server to route 192.168.2.1 to your external gateway.
ASKER
ibidata

The ip you gave would still be on the same subnet as our current network.  My current DHCP server is on a Windows 2003 server on the 192.168.2.x network.  How would I hand out ips to the phones?  Can I use the same ethernet connection and switches as the computers but use a differnet IP subnet for the phones?
Amirchoupani

Subnetting is possible but will not help as your network is out of IP addresses. You should use a different subnet on your new VLAN (IP phone VLAN). For example: 192.168.3.0/24 or whatever possible.
Think VLANs like different subnets that are connected with each other by a router. Except in VLANs there is no real separate physical networks.
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Kyle Abrahams

sorry, am used to the 1.1 subnet.  Yes, switch to .3.x as Amirchoupani had said or something else to suit your needs.
zhuba

There are two main ways that you can set up subnets here.

The first is to use a second NIC on your server on the 192.168.3.0/24 network and have all the phones physically connected through a different network. The second (much better) is vlans as previously mentioned. This involves essentially turning a layer3 switch into a router for certain ports, and assigning itself an ip on a different subnet for any connections coming in through that port. Just remember to enable BOOTP relay to your dhcp server or else your phones won't be able to dhcp
ASKER
ibidata

Will a separate vlan work with the phones and computers connected to the same ethernet connection and same port on the switch?  How will my DHCP server hand out addresses for both networks?
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Kyle Abrahams

To make it work using the same switch:

1)  Create a new pool (192.168.3.x)
2)  Add MAC reservations for each phone for this pool

Switch will be able to forward without crossover, it's just a matter of getting the phones the right addresses.
ASKER
ibidata

I can create a new pool (192.168.3.x) on the same DHCP server with a 192.168.2.x ip address?  How will the phones be able to find the DHCP server with the NIC of the DHCP server on the other network?
Kyle Abrahams

You need to add another IP to the nic on the server.

EG: NIC address 1 - 192.168.2.1 default GW of whatever (remains the same)
       NIC address 2 - 192.168.3.1  Hosts pool for these mac addresses.

When a phone comes online, the phone will broadcast out "Hey, my MAC is <SomeMac>, does anyone have an IP address for me"

It will hit your DHCP server, which will compare it against it's pools and then assign it an appropriate IP address.

Just be aware, if the phones ARE NOT reserved they might end up in the 192.168.2.x subnet.

Come to think of it, you will need to add reservations for your PCs as well so there are no crossovers.




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William Peck
Kyle Abrahams

If you have smart switches (eg: not hubs) you can configure the vlans at the switch level by port.  (EG: every port has it's own default GW).

Phone's default GW would be 192.168.3.1
PC default GW would be 192.168.2.1

the DHCP would respond to wherever the address came from.  

Saves you the hastle of doing all the reservations but you have to configure all the ports on your switches.
zhuba

Not all switches allow vlans. Hubs broadcast to everybody and clog the network, "dumb" switches forward packets to the correct port, and layer 3 switches (aka smart switches) allow configuration of vlans.

Unless you want to mess with vlans and routing, it sounds like a /22 supernet would be a good idea. Just make sure you take the necessary steps to cut down on broadcasts (IGMP snooping, broadcast storm control and BOOTP relay on the switches, and making sure you have DNS/WINS server set up to avoid the need for unnecessary broadcasts).
ASKER
ibidata

After doing some reading and discussing with our phone vendor we will set up the phones with a VLAN on a separate subnet with a separate DHCP server..  When the phones ask for a IP address from our primary network DHCP server there is a setting that we can set to distinguish that if it's a phone it will forward to the phone DHCP server.
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ASKER
ibidata

After doing a lot of reading I decide to put our phones on a separate IP network range and VLAN than our computers.  That way there is less traffic on our voice network and we can prioritize traffic separately.

When the phones look for an IP address they contact our main DHCP server.  The DHCP server has an custom scope option 125 that tells the phone to look for the phone DHCP server on the phone network.  The default gateway on the computer network has a route to the phone network.  The phone DHCP server is a multi-homed server on both networks that can route traffic between the two networks using RRAS.  The server NIC on the phone network was set up on the switch port to only allow phone VLAN traffic so that computers won't ask for an IP from it.    
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Kyle Abrahams

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