How to prevent one pc to "attack" other pc´s in homenetwork?

Stephen0352 · 23 Feb 2015

Hi folks
This just might be a Windows 8 question, but two Windows 7 laptops are also involved, and the solutions might be identical for both operating systems. Here goes:

My firewall keeps telling me it "has blocked a network attack", and looking into the MAC address etc. I´ve discovered that one of the 4 laptops in our home network constantly 'attacks' the others. No harm is done, but it´s pretty annoying.
We have a wireless router, 2 laptops with Windows 7 and one with Windows 8. The last is the 'attacker', an I presume it is a question of some settings, that we could change. We are not using shared folders or anything like that, and the only shared device is the printer. We have not had attacks from any of the other laptops.

Where in the system (Windows 8) do we go to find the relevant settings to change??

Barman58 · 23 Feb 2015

Sounds like the one laptop is assigned the master browser role, (that's normal

), and the firewall is not set to allow the ports used to check the other devices.

You would need to set the firewall to allow the communications on various ports over your local network segment only, The quick way is to allow communication on the standard ports 1-1024, but better to start with 135-139 and 445 and then check to see if any other ports are being used.

Personally for the number of devices you have and the fact that no real damage is likely I would not worry as the only issue is filling a log

A list of ports is available here ...

List of TCP and UDP port numbers - Wikipedia, the free encyclopedia

If you want to investigate what each port is used for

Stephen0352 · 23 Feb 2015

Hello Barman
Thanks for the quick answer! Yes it is a 'port scan', and sometimes the scanned ports appear in the alert message, sometimes not.
My firewall support also told me not to worry, but it´s like if you keep hearing some disturbing noise, when you´re working, you become curious and want to stop it, right? And I always like to learn something new.

If I understand you correctly, I have to open some ports on my pc, or 'allow communication', and then my firewall will not interprete the scan as an attack?
My pc is the administrator on our network, so what is this 'master browser role', that you mention, all about? And why this 'checking other devices'-action? Seems that only the windows 8 laptop does this.

Barman58 · 23 Feb 2015

The master browser is an old server role used by windows networking in a client server system you can set this to be a server - with the workgroup type network there are various rules that are applied by the workgroup systems and one device is allocated the role, which can change for no apparent reason

the master browser is just responsable for keeping a record of the netbios information and matching this to MAC addresses etc. to allow file and print sharing.

To prevent errors being written to the log, you need to "open the ports" on each machine to all other devices on your network - some firewalls have an option to open all the standard windows systems ports - some require you to manually open them.

If you get the port number in an event error you can check what the port is used for and decide if you want to open it or monitor attempts to use the port

Stephen0352 · 25 Feb 2015

Hi, you´ve given me some clues to work with. I´m just having a new modem installed, so when I´ve looked into the whole thing, I´ll follow up on this issue. Thanks!