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Unknown computer shows up on my LAN?
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macbarry
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Oct 22, 2003, 09:31 AM
 
I have a cable-broadband internet connection at my home. I split the signal from the cable modem using a Linksys router (BEFSR41 - 4 port) to 4 different Macs - 3 using OS9 and one using OSX - via ethernet.

Using the OSX machine, a couple of days ago I choose "connect to server" and find "Joe Blow's Computer" listed among my other 3 Macs. I have no clue who "Joe Blow" is or why his machine is showing up on my network.

Using my OSX Mac I disconnect the router and connect directly to the cable modem - Joe's Computer is gone. OK so maybe it's a router issue - but my questions to Linksys are ignored because they are "not responsible" for any issues dealing with an OS other than Windows.

Anyone know what might have happened and why I have been seeing this unknown machine on my local ( I thought closed) ethernet network?

Any ideas on how I can rid this unknown machine? Have I been hacked? Is this a Linksys issue? I'm not sure if Joe Blow is an innocent bystander or nefarious hacker... yikes! Any ideas greatly appreciated.
     
southtdi
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Oct 22, 2003, 03:03 PM
 
Could Joe Blow have got a trojan horse on your computer somehow and is now sucking off of your network? I have seen this with windows machines before. Only thing I could think of.
     
RBattin
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Oct 23, 2003, 12:32 AM
 
Do you have file sharing enabled on your OS X Mac? Does Joe Blow show up as the computer name assigned in System Preferences/Sharing/Computer Name? If you disable file sharing does Joe Blow go away? It's you!
     
ghporter
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Oct 23, 2003, 05:44 PM
 
Cable providers have to configure their part of the network so that neighbors don't have access to each other's LANs. Some providers do a fine job, others don't. Maybe yours needs to know that you can see your neighbor's computer.

Glenn -----OTR/L, MOT, Tx
     
macbarry  (op)
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Oct 23, 2003, 09:31 PM
 
Originally posted by GHPorter:
Cable providers have to configure their part of the network so that neighbors don't have access to each other's LANs. Some providers do a fine job, others don't. Maybe yours needs to know that you can see your neighbor's computer.
Thanks for everyone's ideas.

My file sharing is off, my firewall is up and when connected to my router I still see Joe Blow's computer...

Meanwhile, I did call the cable company. They were the very first people I checked with. They suggested that I disconnect the router from the OSX box and connect directly to the cable modem and that if Joe Blow's computer disappeared then it was the router... I did that and Joe's computer was not visable. However, I still don't get how this could be a router problem?? This is starting to drive me crazy...
     
John Strung
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Oct 23, 2003, 09:59 PM
 
When you tried without the router, did you check to make sure you were in fact connected?

The router can't possible make you see an external computer that you can't see with a direct connection.

If that is happening, Joe Blow's computer must be a connection coming from one of the other computers on your LAN. Try unplugging the router from the modem and see if Joe's computer disappears.

I take it your router is not a wireless router and none of the computers on your LAN have wireless cards?
     
macbarry  (op)
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Oct 24, 2003, 02:34 PM
 
Originally posted by John Strung:
When you tried without the router, did you check to make sure you were in fact connected?

The router can't possible make you see an external computer that you can't see with a direct connection.

If that is happening, Joe Blow's computer must be a connection coming from one of the other computers on your LAN. Try unplugging the router from the modem and see if Joe's computer disappears.

I take it your router is not a wireless router and none of the computers on your LAN have wireless cards?
The router I'm using is NOT a wireless unit and none of my 4 LAN computers has a wireless card.

Yes - I checked to make sure the internet connection was fine when I connected directly to the modem. When i was connected directly to the modem Joe Blow's machine disappeared. This is what implicated the router (in the cable companies assesment) but I am at a loss to understand how the router could cause me see Joe Blow's machine.... arrgh!
     
John Strung
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Oct 24, 2003, 03:06 PM
 
Did you try unplugging the router from the modem to see if Joe Blow's computer disappeared?
     
macbarry  (op)
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Oct 24, 2003, 11:15 PM
 
Originally posted by John Strung:
Did you try unplugging the router from the modem to see if Joe Blow's computer disappeared?
Yes I unplugged the router from the modem and Joe Blow's computer went away.
     
John Strung
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Oct 25, 2003, 09:37 AM
 
That is really strange. I can understand why you would see someone else's computer even if you have a router, but I can't understand why you would not see the same computer if you didn't have a router.

The fact that you can see someone else's computer when you are using a router is not a security concern. It simply means that either they have no firewall or have open ports on the firewall. Your router should act as a firewall preventing them from seeing your computer.

But what I don't understand is why you don't also see the other computer if you are connected directly to the modem and can still connect to the internet directly.
     
macbarry  (op)
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Oct 26, 2003, 01:47 PM
 
Originally posted by John Strung:

But what I don't understand is why you don't also see the other computer if you are connected directly to the modem and can still connect to the internet directly.
Yes - even with my limited knowledge of networking the lack of ability to see Joe Blow's computer without the router is the strangest phenomenon in all of this. The cable company appears justified in suggesting it's an issue i need to persue with Linksys but clearly my router is using the cable and Linksys refuses to answer my questions because I'm using MacOS!

I have decided to assume that Joe is probably just an innocent in all this (I can see when he turns his computer off and on!) and would be just as interested as I am in resolving this problem. I was going to connect to his computer and post a read me file to his hard drive - but was ultimately unable to gain access.

Meanwhile, if I have file sharing turned off for my OSX machine Joe cannot possibly (let's hope!) see my computer. However if I leave file sharing activated for the other 3 OS9s in my LAN and allow them to connect to the internet via the router will Joe possibly be able to see those computers??
     
John Strung
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Oct 26, 2003, 09:49 PM
 
Your router should act as a firewall preventing access to any computer on your LAN unless you have opened TCP Port 548.
     
RBattin
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Oct 27, 2003, 04:49 AM
 
Is the IP address of Joe Blow's Computer in your subnet? What about your three other Macs?
     
stevesnj
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Oct 28, 2003, 12:33 AM
 
Go to the DHCP clients table and delete Joe, turn off all the other systems on the router unplug the router for a min plug back in re-start your computers...and then Joe should be blown. If hes still there do a hard reset on the router.
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Love Calm Quiet
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Oct 28, 2003, 09:18 AM
 
Thanks for suggestion. For those of us not accustomed to digging in the bowels of DHCP, could you telll us where to find the "DHCP clients table". I'm looking at Network Preferences and see space for (optional) entry of "DHCP Client ID" and I see my Airport ID or Ethernet address.

Should this be in an admin app for the particular router or something?
     
John Strung
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Oct 28, 2003, 09:31 AM
 
I think Steve meant the DHCP client table in the LinkSys admin program at http://192.168.1.1
     
Love Calm Quiet
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Oct 28, 2003, 10:14 AM
 
Okay. Thanks for clarification. I'm watching this thread for possible implications to an ABS-centered network.

Guess I should watch it now as relevant whether to consider working with LinkSys router solutions!
     
macbarry  (op)
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Oct 28, 2003, 03:42 PM
 
Originally posted by stevesnj:
Go to the DHCP clients table and delete Joe, turn off all the other systems on the router unplug the router for a min plug back in re-start your computers...and then Joe should be blown. If hes still there do a hard reset on the router.
I'll see if I can find the DHCP clients table and delete Joe. however I don't understand what you mean by "hard reset"...

Meanwhile, could anyone explain why I would see Joe Blow's computer only on my OSX machine and not on my OS9 boxes connected to the same LAN?
     
John Strung
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Oct 28, 2003, 04:00 PM
 
Maybe Joe Blow's computer is not a Mac. OS X will let you browse for Windows computers. OS 9 won't.
     
macbarry  (op)
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Oct 28, 2003, 06:18 PM
 
Originally posted by stevesnj:
Go to the DHCP clients table and delete Joe, turn off all the other systems on the router unplug the router for a min plug back in re-start your computers...and then Joe should be blown. If hes still there do a hard reset on the router.
OK as I type this Joe's computer is still showing up on my "Connect to Server" listing. I have now found the DHCP client's table but i only see 4 IP address - and they appear to all be those of my own 4 computers.

I can easily connect to joe blow's computer as "guest" and have it show up on my desktop but cannot see anything on his hard drive - or copy anything to it ( I tried to alert Joe about all this).

However, I CAN see info about Joe's HD by selecting his HD icon and performing the "get info" command. I can see all the usual info about a HD including creation and modification dates, capacity and available space. format is listed as AppleShare...
     
Scarpa
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Oct 28, 2003, 08:53 PM
 
Have you considered that it may be one of your own machines? Try turning them off one by one to verify they aren't "Joe Blow's Computer". Also, your main machine that is seeing this computer isn't on the DMZ port of your router is it?
     
stevesnj
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Oct 28, 2003, 09:38 PM
 
hmmm...try disconnecting you cable modem from the router then try 'connect to server' if Joe is still there its a local machine,partition on another machine. If he only shows up while the cable modem is connected it seems there is a neighbor's computer with a share on their system and you can see it. Do you have a neighbor called Joe? If not call the cable company they have a problem with the node in your area and they need to fix it ASAP because the system is more wide open than you can imagine.
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macbarry  (op)
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Oct 29, 2003, 10:10 AM
 
Originally posted by stevesnj:
hmmm...try disconnecting you cable modem from the router then try 'connect to server' if Joe is still there its a local machine,partition on another machine. If he only shows up while the cable modem is connected it seems there is a neighbor's computer with a share on their system and you can see it. Do you have a neighbor called Joe? If not call the cable company they have a problem with the node in your area and they need to fix it ASAP because the system is more wide open than you can imagine.
I've checked (again) and Joe is not coming from one of my other machines - at least not that I can tell. I'm not sure what the DMZ is but the OSX machine (only one that see's Joe Blow's computer) is in one of the standard ports on the Linksys 4 port router.

I do not have an immediate neighbor named Joe - but I live in a relatively small town (30K population) and have found a name in the telephone listings that might be him...

I'm beginning to think that this is very likely to be the cable company's problem in spite of the maddening fact that Joe's computer goes away when I connect directly to the cable modem.

This is an incredible issue and one that obviously needs to be investigated further by the folks at the cable company. Since i'm on a Mac however I'm worried about the level of competancy from them... I'm already paying their monopoly a BUNCH of money each month and I just found out that they are increasing my bill by %15 with no additional services! Arggghh where's the competition when you need it?

Sorry for the mini-rant - and thanks again to everyone who has responded. I'll be sure to post new develpoments in this strange tale as they develop.
     
ghporter
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Oct 29, 2003, 05:37 PM
 
There is no way that the computers you put on your router are showing you the foreign computer. There is also no way for your router to "invent" some other computer. Since all the clients listed in your router's DHCP client list seem to be yours, it seems extremely unlikely that the problem is your router. Much more likely is the possibility that your Mac shows different things when connected to the modem because it detects that the modem is a different connection-the modem probably uses a different subnet for it's DHCP IP address assignment than the Linksys router does.

(From a communications-electronics maintenance background of over 25 years, I can tell you that your cable company's blaming a problem on "the other guy's stuff" is amateurish and unprofessional. It also displays a lack, both of respect for the customer and of technical expertise.)

My only non-cable company thought is that at some point in the past, you tried to connect to a server that wound up being called "Joe Blow's Computer." Your Mac remembered that. But when you connect directly to the modem, instead of through the router, the Mac recognizes that it's a different connection, and it never saw the bogus server on THAT connection, so it doesn't show up.

If I'm not mistaken, OS X remembers servers you've connected to on each specific connection, and offers you the choice of connecting to them when you choose "Connect to Server." There must be a way to delete either single entries or the whole list, but I don't know how to do that.

Glenn -----OTR/L, MOT, Tx
     
stevesnj
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Oct 30, 2003, 05:01 PM
 
There must be a way to delete either single entries or the whole list, but I don't know how to do that. [/B]
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