IS this a network problem?

[Funky_Munkey]

Okay, so here's what's going on:
I'm living in a house with 3 other people who are all even more technologically-challenged than I am, but I don't know all that much myself, so we're stuck.

We have our computers networked using a switch, and everything was working fine until last week. One girl couldn't get her computer to connect to the internet, even though everyone else's worked fine. We checked her computer for viruses, etc, and didn't find any. We restored it to an earlier time (twice, actually) to see if that would work, and it didn't change anything, so we undid that. We had already restarted the switch and the main modem, and they didn't work at first, but then restarting them later seemed to work - she was connected again. The next morning, her computer wouldn't even start up, so she said she had it reformatted again. Then, I think, everything was fine. Later, another girl's computer stopped connecting to the internet (this was in the middle of the day, and I'm told that the first girl restarted the switch and modem early that morning). It hasn't been connecting properly for a few days now, but the other 3 computers in the house can access the internet without any problems. We installed Ad-Aware and Microsoft Antispyware on her computer and deleted the 14 or so adwares that were found, but even after running the programs (along with her regular antivirus program) a few times, it still won't connect. These programs do not have the latest definitions installed, since she can't connect to the internet to download them, so if she does have any of the newer adware/spyware/viruses/etc, we can't tell.

One of the girls here is sure that the problem lies in the router/switch, because someone she knows had a similar problem and it went away when they got a new router. I've been told by someone else that it's not a router problem because they too had a similar problem and it was because the one computer on the network had viruses and stuff like that, and the network would kick it off before allowing it to connect to the internet - so, when the viruses were gone, everything else went back to normal.

So... basically what I'm asking is... what's going on?! Does it sound like a problem with the one computer that won't connect now, or is it a faulty switch (even though it's only a few months old and we haven't had any other problems with it so far)? Any help would be GREATLY appreciated!

[bAdWaYz]

Sounds to me like it could be both or a little of each. First thing you want to do is make 100% sure all computers on the network are clean. Our Cyber Safety forum here at CTH is the best on the internet for helping folks find and get rid of nasty internet monsters. Next thing to do is be sure of the type networking equipment you have. I note in the post you say switch the swith/router then you talk about a main modem ect ect. What we need to know in order to help is what do you really have? Do you have a cable or dsl modem that connects to at least one computer then from there to a switch or what? Knowing what devices you actually have and what the network layout is will help us to better help you. So the basic advice I have is make a post in the Cyber Safety forum asking for help with the computers you feel may be infected. Then post back in here with the above mentioned info.

[Funky_Munkey]

I made a post in the Cyber Safety forum, so hopefully help is on its way there...

As for the network layout, we have a cable modem which is connected to a switch (LINKSYS 10/100 Workgroup Switch), which is then connected to each of the 4 laptops in the house.

[bAdWaYz]

Thanks for the info this makes things a bit more clear on our end. I think I see the problem right now but just in case lets ask a few questions. Most cable ISP's will only give you one public ip to use on the internet. In other words lets say laptop1 is connected to the switch. Well that computer gets an ip address from the ISP's dhcp server and gets on the internet all is well. Now while laptop1 is happy surfing another person with laptop2 boots up and tries to get an ip address from the same ISP dhcp server. The dhcp server see's that an ip is already in use for that household and will either grant it to the new connection "laptop2" or it will decline the request from laptop2. Thus either laptop1 gets kicked off the internet or it keeps the connection but laptop2 can't get on the net. You can check with your cable provider and ask if they allow more than public ip per computer but my guess is they will say no. The workaround for this is one of two things. Choice A is to buy more ip's this is expensive and most ISP's won't even let you do it for home use. The other option is to network the computers using NAT or network address translation. NAT will take the one public ip and break off private ip's for use with the other computers so basically you can use 1 ip yet still connect all 4 computers to the internet. The easy way to get this done would be to buy a nice wired router. Any brand will do but I personally like linksys or dlink. Then you would plug the cable modem into the WAN port on the router and each of the 4 laptops would plug into a port on back of the router. There is another way to go but is a little harder to setup and less stable not to mention less secure.

The other way to network the computers would be to use ICS or "Internet Connection Sharing" to allow the other computers to use the net all at the same time. In order to use that you would need one of the computers to have 2 network adapters installed. That computer would be the host computer. You would enable ICS on the network adapter that is directly connected to the cable modem. Then with cat5 going from the 2nd network adapter to a switch. Then the other 3 laptops would plug into the switch. While cheaper as stated above it is hard to setup for a novice, less secure, and far less stable than using a router. Not to mention the fact that if you all want to be on the internet the host computer must be on and connect at all times for the others to use the net. I hope this info helps and if you have any more questions or comments feel free to post back.

[Funky_Munkey]

Okay, what's the difference between a router and a switch? I was under the impression that they were the same, if not very similar and serving the same purpose. I think that's what the guy at the store said when we got it back in the summer.
In any case, I went and checked out the modem and switch wiring, and there's a cable from the modem going into the "uplink" port. Then there are 8 ports, of which 4 are being used for the laptops in the various rooms in the house. So, to me anyway, it sounds like we have the place set up like you suggested...
I also just checked into our IP situation, and with the package we have from the company, we have 3 IP addresses.

Someone elsewhere told me to try:
click start
select run and type cmd
now type ipconfig /release
wait till it does it's thing and show everything as 0
now type ipconfig /renew
wait for it to do it's thing and then try to connect to the internet and see.
Any idea of that will do any good on the computer that won't connect?

[bAdWaYz]

Ok thanks for the update the info helps. First a switch and a router are very different devices. A switch will take packets "data from the internet or a network" and passes them along to the computer that they are meant for. It does this by "learning" what computer is connected to what port on the switch. For example if computer1 is connected on port1 then traffic will pass to port1 and the switch will associate that port to computer1 and all trafic sent to computer1 from then on will only pass into port1. A router on the other hand can not only switch packets but also router them. The easy way to think of a router is to think of a device that can receive, switch, and manipulate the packets that pass into it. Unlike the switch that will just send traffic to a port a router will take the traffic look at it and depending on how you have it setup send it on the way, block it out, or change it in some way. Routers also have build in firewalls that a computer can "hide" behind for extra security.

Now as to the issue you are having at the moment. You say that the ISP has given your connection 3 seperate public ip's. Thats pretty awesome but you still have 4 computers that need ip addresses. The end result is if laptop4 wants to be on the internet you will still either need a router or to use ICS along with the switch in order to make that happen. If 3 computers grab the 3 ip's you have available to you then the 4th computer is either going to knock one of the first 3 off or it won't be able to connect itself. You could call the ISP and ask them if you can pay for one more ip but I still think it would be far cheaper to buy a router. You can still go the ICS route as long as one of the computers has 2 network adapters. Since these are all laptops you likely have 1 built in ethernet adapter and if they are fairly new a slot that you would have to install another ethernet adapter in. The reason you would need a router over the switch is because a switch will not do NAT "network address translation" but a router will. ICS does the same thing but much less stable or securely. There is the info I can give you, I hope it helps and if there is anything you need more help with feel free to post back. Maybe some of our mod's or other members have some advice they would like to offer on this subject as well.

[Funky_Munkey]

Alright, thank you VERY much for your help!

As of today, my computer stopped connecting for a while, then the one that hasn't been connecting in a week or so started! Then we were all off again... Very frustrating!
But I think we have it figured out for the moment, and with the info you gave me, I think (hope!) we'll be okay from here on out!

Thanks again!