Computers showing up on network that aren't mine

[raudf]

This is a question going out to all the IT/network types, concerning an issue of "Seeing computers on my network, but when I remove the modem, they vanish." It's got my local ISP/phone co-op completely stumped. Not hard, given they aren't IT/networking, but phone guys having to take on the job of doing ISP support.

Now for the meat of the matter. I recently got my own connection with the phone co-op and because it's "zoned" (I have no idea what they mean by that, either) I have to use their modem. Well, since then, I've been seeing odd computers on my network that wasn't there before. Around 5 in all, with 4 of them being online all the time, and one blipping on and off. Removing the modem from my network makes them vanish. If I plug the modem into my computer, they appear. Network map shows that it's coming off the modem. This modem is NOT WIRELESS. I also cannot access the modem, so I can't do any sort of settings check.

I've put in several calls to the phone co-op's ISP support and I either get a "They're left overs from your network," "You'll probably see them," and ultimately, from the tech sent out to look, "I have no idea but it's not on our end."

I'm pushing at the sucky point, because I don't like having comps showing up that aren't mine or me-approved. Does anyone have an idea what might be causing this and how I can stop it? If it's something I can stop, because if it's something I can't, I'm documenting it so I can take it up the chain until this is resolved.

[csquared]

Sounds like your ISP has F'ed up big time. Continue to push for a fix. What your probably seeing is other customers on the shared ISP network.

In the mean time, you can install a router/firewall between your network and the modem or make sure that you have enabled a software firewall on all your computers.

[It's me]

Sounds like your ISP has F'ed up big time. Continue to push for a fix. What your probably seeing is other customers on the shared ISP network.

In the mean time, you can install a router/firewall between your network and the modem or make sure that you have enabled a software firewall on all your computers.

+1

Note that you may have to change the modem to "pass through" mode in order to let the separate router to do its stuff.

[raudf]

Sounds like your ISP has F'ed up big time. Continue to push for a fix. What your probably seeing is other customers on the shared ISP network.

In the mean time, you can install a router/firewall between your network and the modem or make sure that you have enabled a software firewall on all your computers.

Already have a firewall enabled router between the modem and the rest of my network. It's wireless and password protected, for the hand-helds. That was the first thing that I insisted on.

Thank you, CSquared. I have come to the conclusion that I know more about the network than they do.. and I know I know nothing. I wish like heck that there were other providers in my area, but unfortunately, the co-op owns every f'ing thing concerning the area.

So, since a relative suggested it, would asking for an IP change fix it?

Edit to add: Called the phone co-op and worded it exactly as you did, "I see other customers on my network." When I was able to provide Mac addys for the computers that lit a fire under 'em.

[TheSHAD0W]

Okay, I can tell you exactly what's going on.

Windows includes a mode of operation that helps computers connect with each other over a private network. It was basically meant for small businesses way back in Windows 3.0 days (possibly earlier). When you're connected to your ISP, you're basically on a shared line with other computers also connected through it, and thanks to Windows being helpful, you're all connecting with each other. This can indeed be a security risk.

One solution is to install network security software, such as Comodo Firewall. You may already have security software that's capable of handling this issue, but you may have mis-configured it. This is the important point: When the software asks you what type of network you're on, do not select "home". Instead, select "public". This will prevent your machine from connecting with others via Windows sharing.

Another good way of fixing this problem is to use a cable/DSL router on your connection. These devices are handy for several reasons; they can provide Wi-Fi for wireless devices; they can allow you to connect multiple computers to your internet uplink; but importantly, they isolate the public network from the network inside your house. Computers all plugged into the intranet ports (and Wi-Fi) on the router are able to see each other handily, but machines from the outside can't get in.

[otakuneko]

Already have a firewall enabled router between the modem and the rest of my network. It's wireless and password protected, for the hand-helds. That was the first thing that I insisted on.

If there's a router between you and the modem, you should not be seeing this behavior. Typical consumer-grade routers will not allow unsolicited comms (such as netbios broadcasts) to pass from the WAN port (where the modem should be plugged in) to the LAN.

[sms001]

What's the telco provided modem model?
What protocol does the telco use? (PPPoE, PPP, etc.)
Has the telco had you do a hard reset of the modem?

What's your router?
What security is enabled on it?
Are you broadcasting your SSID?

What version of Windows?

When you say "see them on my network" do you mean they show up as machines/shares in 'Network Places' (or your equivalent) or do you see them in a log from the router, or in its DHCP table?

If there's a router between you and the modem...

Yeah, this is the strange part.

[raudf]

I see them in the Win 7 version of 'Network Places,' but on the map, they show up as being "not on my home network," but rather between the modem and the "internet" if you will.

Turns out the service is "bridged" in my area and is part of a "zone drop box." Not too sure on the "zone drop box's" meaning, because I'm used to my home network. Doesn't matter. In a minute, I'm taking down my network and playing with my main router to make sure it's settings are okay, since I can't access the modem.

[retro]

Can you block MAC codes on the router? I restrict mine to only allow my computer/tablet.

[raudf]

Now that I've completely rewired everything, the computers have vanished. I get the feeling someone (either my dad or the guy doing the set up for the modem) wired it up wrong. Had to reset my wireless router, so made sure it was password protected again, along with the firewall, which wasn't... and I will kill whomever fiddled with that setting.

[TheSHAD0W]

I've thought about this some more, and if someone was fooling with the router settings, they might've set that computer as the DMZ host. This would allow SMB communications through between it and other computers on their network.