How can two computers share our AT&T DSL?

We have a Siemens Speedstream 4100 modem (for wired connections) with AT&T DSL and I have the modem connected to an unmanaged HP Procurve 2124 switch.

Desktop connects to switch and internet works fine. If I connect a laptop to the switch, I get an IP address conflict and can’t use the internet on either computer.

Any suggestions?

Sounds like the laptop is set to a fixed IP address. Go into network connections, pick the Local Area Connection, select TCP/IP, click Properties, and change the setting to Obtain an IP Address Automatically.

That only works for a router.
Since it’s a switch you have to manually set IP address. Look at the TCP/IP settings on the desktop. Now go to the TCP/IP settings for the laptop and make them exactly the same…except for the IP address. The IP address should be the same, except bump up the last part of it by 1. So if it’s 192.168.1.101 change it to 192.168.1.102.

This is all based on your desktop settings being set to manual. If it says “obtain IP address automatically” something else is going on.
(You could most likely change the last three digits to anything, but this is easiest)

Just checked and both the desktop and laptop are set to DHCP. As soon as the laptop was plugged in, the desktop had a message saying “IP address conflict with another system on the network”. At the same time the laptop was saying “Aquiring and address.”

If I understand this correctly, you are trying to connect two computers to the internet without a router, just the modem.

If so, this may not work as some ISP’s won’t let you have two IP addresses on one subscription.

You will probably need a router. A router will hand out two IP addresses while your iSP only sees the one IP address. A switch won’t hand out IP addresses (aka DHCP handling).

A cheap router is about $40, medium router $75, a really nice one can be $100. If you are not gaming, usually the El Cheapo will work. If you can afford it, go for the medium price.

If however, I have misunderstood, then feel free to disregard.

Have they worked together in the past?
Two suggestions…
1)Try rebooting everything, laptop, desktop, switch (are you sure it’s not a router?)
2)on one of the computers go to Start->Run and type CMD [Enter]
From the command prompt type “ipconfig /release”[Enter] then “ipconfig /renew” [Enter]
If that doesn’t work, we can just manually set IP addresses, won’t take but a minute and will probably resolve your issues. But if we can get everything running with DHCP it’ll make things easier in the future.

Okay, looked up the model number, it’s a switch, here’s what you need to do.
Go to the desktop TCP/IP settings. Change it to manual and use these settings
IP 192.168.1.100
Subnet 255.255.255.0
Gateway 192.168.1.1
Preferred DNS 8.8.8.8
Alternate DNS 8.8.4.4

On the laptop use the same settings but change the IP to 192.168.1.101

Actually, before you start this, go to Start->Run CMD and type ping 192.168.1.1 and make sure get a response. I assume the IP address for the modem is 192.168.1.1, but we should double check. If you don’t get a response we have to find out the IP address for it. If it’s not 192.168.1.1 it’s probably 192.168.1.255. We can deal with that later.

You understood perfectly and now I understand what’s happening.

My next goal is to make a wireless network. Can I get a wireless router? And can I use it for wired connections too, as I don’t really need the desktop to be wireless and one laptop doesn’t have a wireless feature?

There are plenty of cheap wireless routers out there with some wired ports on it.

I have yet to see a wireless router without at least one wired port, since you need to be hardwired to it for the initial setup. Most have four.

Thanks folks! Gotta love the SDMB. Also Amazon. (Just ordered a Cisco-Linksys WRT160N-RM Refurbished Wireless-N Router for $31, no tax, no shipping and I’ll have it Wednesday).

This would work perfectly to just have two computers sharing files, it will not work however with sharing internet as the vast majority of internet providers will only issue one IP address to a typical home user. A router can issue multiple internal IP addresses that all use the same internet IP address. We can get into internet connection sharing in windows but thats kinda the messy solution to a problem that can be solved with a $40 part.

You also would not always want to manually specify the DNS.

I originally mentioned having the Primary set to 192.168.1.1 and leaving the alternate blank. But if the modem turned out to have a different IP address it would just be another thing to change, so I figured I would just put in one that I knew (read: assumed) would work.

Other then that, why wouldn’t my setup work for the vast majority of internet providers? The OP has a switch. IME plugging your modem into the switch, and plugging all your computers into the same switch with manually set IP address works just fine.
Did I miss something?

Some modems are routers and some are bridges. For example, I had an Actiontec DSL modem which only had one ethernet port, but it was a router. I could have plugged a switch into it, and connected multiple computers without a problem. My current cable modem though, is just a bridge. It converts the network signal over the cable lines to an ethernet signal. It doesn’t do any routing, in that the first device plugged into the cable modem’s ethernet port gets the real IP address from the cable company. This would work fine with a switch and a single device, but with a switch and multiple devices it would not work, even manually setting IP addresses (unless the cable company was willing to provide me multiple IP addresses).

I also had a Cisco DSL modem which could be either a router or a bridge, depending on how it was configured. At one point I also used a USB only DSL modem, which bridged between the phone line and a usb connection. It wasn’t really much of anything, in that the host computer did most of the work. All of these different modems were with the same DSL provider, so it is completely possible that two people, even with the same broadband company, can’t both use the same modem+switch setup. It all comes down to the details.

As to the OP, it looks like that has been resolved with the purchase of a router.

For what it’s worth, the Airport Express from Apple does not allow a “pass-through” connection like you’re talking about. It has one Ethernet port, and you can set it up to either act as a wireless router (by plugging in your DSL modem to it) or as a “receiver” (to add a printer or computer without a wireless card into an existing wireless network.) However, you can’t use it as a router for both wired and wireless connections.

Actually, that would work fine for a switch, too, if you had a DHCP server also attached to the switch.

And it wouldn’t work for a router that didn’t include a DHCP server somewhere in the broadcast domain.

I realize there’s a value in keeping it simple to answer the question, and the vast majority of home routers have DHCP servers included and enabled.

But it blurs the distinction between routers and switches. Your typical home router includes four switched ports on the inside VLAN, one port on the external VLAN, routes and provides NATting between the two VLANs, and provides DHCP services. But just because those features are all found on the box doesn’t make them all router functions.

Bricker, where you said VLAN you mean subnet(or just network). VLANs are a completely different beast that no consumer-grade hardware is going to deal with.

You can get a usb wireless adapter. Here is the first page of a Google search on “usb wireless.” I had one (much bigger) on an old desktop when we first set up wireless.

for the average home user the distinction is pretty much irrelevant these days. In medium to large businesses with more complex routing needs you will see routers without integrated switches and or Dhcp being managed by a server.

nm