I have a cable modem with USB and ETHERNET connections, and I've connected a computer to each. Both seem to work, and I get different IP's on each machine. But when I talked to the cable company they told me it's not re commanded and that it can even seriously harm the modem! Sometimes the machines get the same default gateway address and when this happens some things don't work. Is all this logical? Is it allowed to have 2 IPs?
I'm a little suspicious about the threat of "serious harm" to your modem, and I actually expect the gateway address to be the same.
But whether or not it should work, or whether or not you're allowed to have two IP addresses ... that's up to your ISP.
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I'll start with the modem. Normally those that supply two different connection types, such as USB and ethernet, expect that you'll use one or the other, but not both at the same time. Some may, but I wouldn't count on it. In any case, it'd have to be a very poorly designed modem if trying to use both caused it damage. At worst I'd expect one or the other to simply not work.
Now, whether or not you can have two IP address is totally up to your ISP. They may arbitrarily limit it, typically to one, and usually charge more if you need more IPs. It's also possible that attempting to use two on the same connection can cause confusion, especially for incoming connections. Again, that's totally at the whim and configuration of your ISP. In general, though, unless you're paying for more than one IP, you can probably only use one.
Now, the gateway IP address is fairly simple. That's just the next computer or router upstream from yours that is the "gateway" to the internet. When you communicate to another computer on the internet, the packets you send are physically sent to that gateway as their first step out onto the internet. It's surprising to me that you got two different gateway addresses, but certainly not impossible.
My real recommendation in the situation you describe is to bypass all these questions and work with a more common solution that's designed specifically for what you're attempting to do: a NAT router. Routers are not that expensive, and basically sidestep all of your questions. They're designed to take that one IP address and allow you to share it with two, or more, computers.
It's a much simpler solution.
Related:
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Ask Leo! - How should I set up my home network?
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Ask Leo! - Why does my home network only work with one computer at a time?
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Ask Leo! - How can I use two ip addresses from one cable modem?
Article C2525 - January 19, 2006
Dear Paul,
The motorola SB 5100 requires that you connect the router to the cable modem (both ends RJ-45-Ethernet), in ur scenario through a cross over cable. What you r doing is using a srtaight thro standard cable. Post it whether this solves ur problem or not.
Posted by: SK at September 2, 2006 8:13 AMHi
Posted by: andy at January 7, 2007 7:09 AMIm trying to set up my own network with a lap top to my computer. The computer is connected via usb through its modem. When installing the new router the connection is ethernet, as soon as the usb is disconnected and the ethernet plugged in I no longer have internet connection and cant install the router properly. All the lights on the router are working barring the internet light. Do you have any suggestions as to whats going on?
Hi,
Posted by: Ben at April 6, 2007 9:07 PMAt the moment i have 2 computers sitting next to each other with a surecom EP-808X Switch, and a SURFboard SB5101 Cable modem, I have a Eternet cable going into the switch and two ethernet cables going from each computer into the switch, i can connect on each computer. BUT! I have to dissconnect one because i can only use one I.P. Otherwise they will cancel each other out, how can i fix this problem, i have tried to connect to my modem to add more I.Ps connect but can't find a tab that applies that.
HELP ME OUT!
:D Thanks mail me
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You'd have to talk to your ISP to get more than one IP on the internet.
It's much easier to replace your switch with a router and share the one IP you
have. http://ask-leo.com/how_should_i_set_up_my_home_network.html
Leo
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I cant get an ethernet cable to work with my pc. im trying to connect to a motarolla 5120 but only usb will work .anyone have any suggestions?
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