How to assign a second IP to a NIC that already has a DHCP IP

[jbond04]

Hey everyone, I'm having a problem creating a working LAN in our house. We have a home network in our house that is set up as follows:

Cable Modem--->Switch--->5 computers

Comcast is our ISP, and we also buy additional IP's from them so that each of the five computers gets their own public IP address. Now before you lecture me on how I should get a router, let me tell you that I've been there and it doesn't suit our needs. Some of the applications we use require their own, unique public IP address to function properly.

Anyways, Comcast assigns us dynamic IP's using DHCP, all of which are potentially on different subnets (e.g. 27.12.102.23 and 67.133.142.4). The problem is that our computers can no longer see each other as a result of the vastly different IP's...no file or printer sharing, LAN gaming, etc. What I would like to do is assign a second, local IP address to each computer's network adapter. This is already possible within Windows XP, but not when DHCP is enabled. Windows will allow me to assign multiple static IP's to a network adapter, but as soon as I turn DHCP on, they go away. Does anyone know of a workaround to assign a static IP to a network adapter that already receives a dynamic IP?

P.S. I did a search on google and found a website that supposedly accomplishes what I'm asking, but I tried it out with no luck. Here's the link.

 

[JackMDS]

It does not work because what you see on the Dan Petri's web site are multiple IPs numbers that belong to the same private IP Band, so it is all one cohesive LAN.

You want to assign to the same computer a public IP and a private IP at the same time. No can do.

You did not divulge the "secret" need of the Multi public IPs, so the following is long shot.

You can try to find an old SMC7004VBR; it is a $50 wired router that can put up to 10 computers on the DMZ provided each computer has a public IP (which you have). Using this Router each computer would have a private IP so you would have normal Network, and each one can be on the DMZ to sit directly on the Internet.

YMMV.

:sun:

 

[jbond04]

Thanks a lot Jack. I guess it's a bummer that I can't have both a public and a private IP...would have worked out really well (no additional cost). I don't claim to understand networking at all, but it's strange that I could put two NIC's in each system and then have one NIC pull a public IP and one a private IP, and have that work. Yet this system of assigning two IP's (one public, one private) to one NIC won't work? Oh well. Onto to a bigger, more important issue:

With this SMC router, will each computer still pull a dynamic IP off of Comcast's DHCP server? I guess here's what I am envisioning: Each computer will pull their own public dynamic IP from Comcast (which assigns IP's based upon MAC addresses...so somehow the MAC addresses of each computer should be visible to the modem), which will then be translated into a private IP for each. From there, I could place each computer into the DMZ, opening all of their ports, so no blocking of inbound/outbound traffic is occuring, and every computer is on the same private subnet.

Sounds complicated...glad I didn't have to engineer that.

As for my "secret need", it's not anything shady. Some of the computer games we play (Dawn of War being the primary example) will not function correctly behind a NAT router when 2 or more local players want to play over a single public IP address. Also, it saves me the trouble of opening ports for each user here on our network (which you correctly guessed).

Thanks again for lending your expertise!

 

[Nothinman]

Some of the applications we use require their own, unique public IP address to function properly.

Do what we do, yell at the developer's boss. It doesn't do a lot of good here as the apps still suck, but it makes us feel better and we get to pull it out as to why things are going to cost more whenever they want to sell it to a client =)

I could put two NIC's in each system and then have one NIC pull a public IP and one a private IP, and have that work. Yet this system of assigning two IP's (one public, one private) to one NIC won't work?

It shouldn't work and it would be very bad design anyway, think about it, your private traffic would (or at least could, depending on the wiring) go out onto the Comcast Internet segment before coming back into your private network.

I just created 2 virtual interfaces on Linux (lo:1 and lo:2) and gave them 2 completely seperate IP ranges and they came up with no problem. But I have no idea if they would actually pass traffic if I put them on real interfaces. It might just be a Windows limitation, but in general it's a good limitation.

Some of the computer games we play (Dawn of War being the primary example) will not function correctly behind a NAT router when 2 or more local players want to play over a single public IP address

Some games (Q3 comes to mind) lets you choose the port it uses for communication, so you can just change the UDP port on the clients thant want to play on the same server at the same time.

 

[ITJunkie]

In XP you can assign an alternate / static ip address even if you are using DHCP. Problem is as long as DHCP is grabbing an IP this won't work.

 

[Lordicus]

With Sympatico and a DSL modem, I am able to obtain 4 dynamic public IP addresses (maybe more, I do not have any other PC's).

My network cards are configured with a static internal IP and I use Sympatico's proprietory software to connect to the internet which gives me a public IP.
It creates a PPP adapter and connects to the modem via the switch. I have 4 Pc's connected to the switch and I do the same with each of them.

This sounds like what you need. Maybe you can get your hands on a different modem or some software that creates the connection/adapter. It certainly is possible here.

Hope this helps!