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I am not a server person, or IT professional. I am a software designer who has been thrown into this position for a temporary period until someone can be hired permanently.

My question is more of a general one, I'm trying to figure out how a client has their network setup so I can help them forward some ports (as required by our product).

The client has multiple public IP addresses. (for simplicity we will call them through, and claims to have a single AT&T 2WIRE modem. His ISP has come and setup a device to be publicly accessible via, and the client wants our device on

I have no idea how a single modem would be able to support/server multiple public IPs, and furthermore how I would forward off port(s) to a specific one. Is there any good free articles I could read? Is the client wrong in their claim to have a single modem? I have a Bell 2WIRE modem here in the office to play around with, but as far as I can see in the options it only allows me to have a single public ip. I'm confused, please can anyone help steer me in the right direction?

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4 Answers 4

Maybe your client has a routed subnet to his modem? But you should really ask your client or his ISP. The ISP can tell for sure.

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Some routers/modems only support on public IP address, or don't support them fully and without issues, so you may need to upgrade the modem.

Some don't support multiple WAN-side addresses directly, but can be told to operate in bridged mode where they just ferry packets between the WAN-side and the LAN-side so machines LAN-side can respond directly (or a single PC/router, such as a small Linux box, can listen to all the addresses and map connections appropriately).

If the modem is provided by the ISP then you should ask them for further information - they will know what it is capable of.

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I see that 2Wire make (or made, until they were acquired by Pace) DSL modems. It's perfectly normal for a business-class DSL modem to support a range of local addresses; your choice of sample range makes it sound as if you have a /29 (block of eight addresses, less one for broadcast and one for network, leaving six) being routed to you.

The modem can very likely be configured to do port forwarding as you would wish. But to give any advice at all we would need to know what model of 2Wire modem it is.

I also note that you may not need to do port-forwarding at all; many of these DSL modems have multiple ethernet ports on them which are all on the public address space, and you need only configure your device to have the actual address and connect it to such a port.

But again, this will depend on the device and the configuration, and we will need to know what model of device it is before we can give any advice.

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All that a modem does is turn an analog signal into a digital one. A modem won't do routing, which is what you need. Some modems have a router built in, very few of these handle more than one public IP. You'll probably need to invest in more equipment. You should contact the ISP to make sure that you purchase equipment that's appropriate.

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The 2WIRE modem is a modem/router combo, and I believe that is does only support 1 public ip. However the client claims they have 6 public ips coming into it. I have told them to contact their ISP and have them get in touch with me as I cannot be getting the whole story here. I do think the main problem I am having is lack of understanding / information from the client. –  rlemon Oct 31 '11 at 20:37
this is the problem when you are trying to talk to a group of farmers about their network configuration. –  rlemon Oct 31 '11 at 20:38
Haha, I consider myself lucky never to have been in that situation! –  MDMarra Oct 31 '11 at 23:22

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