Computer Related > Two computers - one internet connection Miscellaneous
Thread Author: Crankcase Replies: 18

 Two computers - one internet connection - Crankcase
I may be employed in IT. I may have spent a happy day delving into the inner depths of a misconfigured hub transport in a semi virtualized Exchange cluster. But when I get back I'm utterly bamboozled by this home stuff.

What I've got - Virgin broadband, using a cable modem. Plugged into that is a DWL-2100AP D-link wireless access point. A Mac laptop using Airport and a desktop PC upstairs with a D-link wireless card in it.

What I want - to get both machines seeing the internet at the same time.

What happens - if one has a connection then the other won't get a valid ip address and so can't "get out" to the net. The only way to make it do so is shut down the working computer, and entirely reboot the cable modem and the wireless access point. I can get the Mac or the PC to see the internet, but not both at once.

It seems to me as though the cable modem will only issue one ip via DHCP and refuses to do another. I tried making the 2100AP a DHCP server but that resulted in no machines getting an ip address at all.

It must be possible to get both machines working at once, surely?

Brain dribbling out of ears now.

 Two computers - one internet connection - Zero
yes the cable modem must have a DHCP server, and the hosts set to dynamic DHCP.

However your modem is not a router, and therefore cant cope with more than one DHCP address on its "lan" side. Its just passing the WAN one on to the PC.

You need a router with a DHCP server, so buy a cable modem one.
Last edited by: Zero on Wed 14 Apr 10 at 22:22
 Two computers - one internet connection - Crankcase
Ok...I think.

In the config of the wireless AP I already have (directly plugged into the cable modem) it offers me the option to set it up as a DHCP server, but when I do that neither machine gets an ip address at all.

If I get hold of a different cable modem wireless router with an inbuilt DHCP server as you seem to describing - what's different to make that work?

Sorry for dullness, not my area.

 Two computers - one internet connection - Iffy
Buy a dongle - means you also have some access if your home system fails.

Last edited by: ifithelps on Wed 14 Apr 10 at 22:34
 Two computers - one internet connection - Crankcase
Last time I came across the word "dongle" it was a bit of hardware that let Autocad work, so I had to google it. No wiser. How does that see the internet? Does it incorporate a phone or something?
 Two computers - one internet connection - Iffy

In this context, a USB stick with a SIM card in it.

If you have a third generation mobile phone signal in your area, access will be almost as quick as broadband.

I have a Vodafone dongle which will use the older mobile network when no third gen signal is available.

Access is then at dial-up speed.

Third gen signals are good in cities and most towns, but not so in rural areas.

 Two computers - one internet connection - Crankcase
Brilliant - thanks for dongle explanation, ifithelps.

I thought you paid pounds per MB down a mobile phone, but never having accessed the net down such a thing I may be out of date.
 Two computers - one internet connection - Iffy
...I thought you paid pounds per MB down a mobile phone...

My dongle is £15 a month which includes, I think, 3gb of access.

I've never come anywhere near that, and unless you like downloading loads of video, I can't see many people would.

Handy to have when I'm out and about with my little netbook.

There are various PAYG tariffs which, like voice mobile tariffs, change all the time.

 Two computers - one internet connection - rtj70
I've got a Huawei access point which has a SIM to access the GPRS/3G networks but also a wifi hotspot. It can let up to 5 clients share the access point to the Internet. Works well.
 Two computers - one internet connection - rtj70
EDIT/SNIP: Seems it is an AP and not a router... there's your problem.
Last edited by: rtj70 on Wed 14 Apr 10 at 23:04
 Two computers - one internet connection - Crankcase
Ah, Zero, got it now. The key word was router wasn't it, as opposed to access point. Thanks, now clear, and I know how to proceed. Pint on me next time you're down this way. You too iffy!
Last edited by: Crankcase on Wed 14 Apr 10 at 22:49
 Two computers - one internet connection - Zero
yup its the lack of router part thats killing you, without it you only have one IP address for the internet for any of your pcs to use so they cant all use it at once.
 Two computers - one internet connection - rtj70
The Dlink product you have can work in five different modes. It does have DHCP. You may have configured it one way and reconfiguring it may get you a shared access point.

Edit: But as Zero says, does not seem to have a router.
Last edited by: rtj70 on Wed 14 Apr 10 at 23:19
 Two computers - one internet connection - car4play
When either machine is connected to the internet and working ok what ip address does it use? E.g on the mac under system preferences what does it say for network->airport. On the pc if you run the command prompt what does it give for "ipconfig"?

The reason is that the easy way to get both machines on the net at the same time is that they share the same outside (WAN) ip address of the Virgin cable modem by doing NAT (network address translation). This would give a connected pc one of the local ip addresses (usually something like A DHCP server would automatically assign this to your pc but is not necessary. Eg Most of our machines here don't use our DHCP server for their configuration.

If your Virgin modem does not do NAT (because it is just a modem and not a modem/router) then you can either
- buy a NAT modem/router instead
- add a NAT router to it (eg. Apple's Airport Extreme will connect to DSL and do NAT and the wireless access at the same time - and DHCP serving if you want that too)
- effectively get one of the connected PCs to do NAT by "sharing their internet connection". You would have to have that pc on for the other to work and you would also have to wire one of the connections because you cant share wireless to wireless for example.
- a final way is to get Virgin to give you 2 WAN ip addresses if they can although this really isnt the way to go at all.

It is better security-wise to be connected by NAT because then any shared services (eg file sharing) are on non-standard ports for people on the outside of your home.
 Two computers - one internet connection - Crankcase
Thanks for all the help everyone. I'm much clearer now.

I'll go down the path of adding a wireless router once I can source one at virtually no cost.

To mop up the other points:

The Virgin modem is provided by them, so I can't replace that.

I thought about sharing the connection, but don't want one of the machines wired.

Virgin aren't going to give me 2 WAN ip addresses. They're going to try to move me to their 50Mb service at extra cost, because that includes (I believe) a wireless router. But that's more money than I want to pay a month and all I need is about a 0.5k connection for logging in here and checking email, with a bit of spoken word Spotify every so often which is about all I ever do anyway.

Can't find much else interesting to do with the internet.
 Two computers - one internet connection - rtj70
>> If your Virgin modem does not do NAT (because it is just a modem and not a
>> modem/router) then you can either

The Virgin Media modem is a DOCSIS cable modem. You cannot replace with a modem/router. You need a 'cable' router, i.e. one without a modem of any sort in it.

The modem issues only one VM IP address so you need a router offering NAT to share the single IP address.

You can get a router for little money though. You could get a cheap one for £20 or thereabouts. Or get a decent one for more.
 Two computers - one internet connection - movilogo
I can't really see why it has to be so complex here.

My ADSL modem stays on all the time.

Any computer in my home (or even neighbours') can see my WiFi network and can connect as long as correct password is supplied.

The IP address at each computer is assigned dynamically.

I have connected to multiple computers (as well as my smart phone) at same time each one running different operating system (Vista, Linux, Symbian).

Is cable broadband configuration different??
 Two computers - one internet connection - rtj70
Cable works no differently although the modem and router are separate devices. The OP's problem is his access point is not a router. Your ADSL modem probably has a router in it as well (most do).

This is not complicated. He's just using the wrong box to share the Internet connection. He could use the AP he has to extend the range of his network though once he has it working or use it to connect a non-wireless device to his wireless network.
 Two computers - one internet connection - Crankcase
Loop closure - had a router lurking about in a basement at work, so have experimentally chucked it into the mix.

As suggested it works - both PC and Mac can now see the outside world simultaneously.

Of course, I had to go one step further and attempt to share a Windows drive and printer to the Mac, and does that work? Does it heck as like. So patience now lost. I hate when something that "everyone knows is really simple" just fails with rubbish.

Never mind, I'll live without that refinement.

Thanks to all again.
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