Turning a router into a gateway

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dkulprit

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Nov 29, 2012
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I have a client that has devices that have to sit on public static IP. Unfortunately the only ISP in the area only provides modems with single ports. Which makes it kind of hard to use 5 separate static IP's while staying PCI compliant.

Is it possible to use a basic switch right after the modem, or would I have to put a router on the network to handle that?

The modem does not have router capabilities, so I am thinking I need to put a router in there to handle the information.

With that being said, would I have to set the IP of the router as the gate way address?
 
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Alabalcho

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Jan 13, 2011
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Unless the ISP can provide 5 real IPs, you cannot make them out of thin air. AT&T have "Business DSL" where they do provide a /29 network. In that case, you could use a switch after the modem, and connect devices directly to the network.

Check with that ISP - what service they do provide. If you can get that, you have to configure these 5 devices with static IP configuration, and the ISP will give you correct details.
 
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dkulprit

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I got that, it is on a /29 or a .248 subnet with set 5 static ip's. But the modem they provided only has 1 port, and has no routing capabilities. Which makes putting 5 separate static ip's on it very difficult. I will need a router to handle the subnetting. But i am confused on how to set it up a little bit.

The modem also does not have a bridging function according to the ISP. I don't know if they just call it something else, but they aren't being really helpful about how their network works.
 
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bill001g

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Aug 9, 2012
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It varies a little bit from vendor to vendor. Technically you have 8 ip since the route the whole subnet but you have to be creative to use them all.

If the modem does not have bridging ability then it must be a router. What you likely have is a wan ip given to you via dhcp and then they route the /29 to that address.

In the simplest configuration you would assign the /29 to the lan port and use DHCP or static ip to assign the 5 ip to the end devices. You would hook a switch behind the router in this configuration.

Now the other way to do this is to use private ip and then one to one nat them. Doing it this way you can actually use all 8 ip addresses. It depends what the router supports.

Hard to say you really need a fairly advanced device to take advantage of real ip addresses. I know some allow you to place another router behind theirs and then route the /29 to that router and let it do the work.
 
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Kewlx25

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Oct 23, 2009
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By standard the first and last IP cannot be used. It may work in some cases, but that does not follow the protocol and may not work in many cases or may have some strange issues. He also loses one from having an upstream gateway to get out to the Internet. So 5.
 
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bill001g

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You must think outside the box to get all 8 addresses to work and really understand how subnets work. I have helped a friend make this work on unverse.

Let say you are assigned 123.123.123.192/29. This normally means I can only use 123.123.123.193-198. But if I set the mask to 123.123.123.0/24 now my broadcast becomes 123.123.123.255 my network is 123.123.123.0 and I can assign the router 123.123.123.1. This means all the other 8 ip are just normal usable IP addresses.

Of course this means if some machine was using 123.123.123.55 on the internet I could not talk to him but I likely never will need that.

There are 2 other ways to make this work. If the server support VIP or Loopback addresses I could just assign say 192.168.0.x to the lan and then route a 123.123.123.xxx /32 to the 192.168.0.x address corresponding to the server. The server would be responisble for generating the packets with a correct source address.

The other way is to do one to one nat address so I can map 123.123.123.199 to 192.168.0.99. This is only a broadcast address when it is used on ethernet since it is not on any interface it can be used.

How much of this you can do on a consumer router I have no clue but it works fine on commercial cisco routers. I have made it work using all these methods on a uverse install....but this particular version of uverse router had the option to in effect static route the block to a secondary router.



 
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