Different IP subnets on one physical LAN

Posted on 2009-05-17
Medium Priority
Last Modified: 2012-05-07
Hello experts,
I inherited a LAN that is making use of an enitrie block of class c public IP address. These IP addresses are being used by LAN servers and DHCP workstations (
This is obviously not ideal and I'd like to eventually change the entire LAN to a private IP address range.
There are 5 servers and about 100 LAN clients.
There is a NAT firewall that will allow the implementation of private IP adress space
For the moment, I'd like to utilize a private IP address space for the DHCP LAN clients ( and leave the servers on their exisiting address space.

Ideally I'd like the LAN clients (on to be able to ARP directly to the servers (on without having to use a router.

The firewall's LAN interfaced is licensed to a specific public IP address (

Any idea's on the best way to go about this.
Question by:MickDoev
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LVL 14

Expert Comment

ID: 24408761

One thing to think about is the public address range you can use. is available and mostly used in business environments.  Not that you need it, but there's a much higher range of addresses available.

Just a thought ..
LVL 14

Assisted Solution

uucknaaa earned 720 total points
ID: 24418549

It's been a few days since you posted the question.  Have you had any thoughts about the address space?

Maybe I'm over simplifying things here, but this design looks real simple to me.  About the only change that needs to be made is the DHCP address range change.  Your existing firewall ( will assign the DHCP addresses on the range of your choosing.  The firewall will act as the internet gateway and all of the servers will remain on with static addresses assigned.

If there is anything more specific that needs to be taken in account, or worked through, please let me know.

Waiting your response.

Author Comment

ID: 24418674
Hi uucknaaa
I would like the DHCP PC's that will be on a different subnet to be able to "ARP" to the servers directly as appose to using a routing table.

Not sure that I wil be able to do exactly what I want here.

Accepted Solution

MickDoev earned 0 total points
ID: 24437717
Looks like I'm going to have to use routing :(

I'm going to create the private IP subnet on a seperate VLAN using a layer 3 switch.

 I don't think its possible to ARP across subnets.

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