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If I connect a second computer to my router using an ethernet cable, how much traffic can that new computer potentially see? Currently I have two computers connected to my router via ethernet cables; one is my personal computer, the other is one issued to me by my work. I understand that the work computer would at least be able to see some basic packet information but I'm wondering if it could see more specific details, or get access to any folders I'm sharing on the network. While I doubt that they're trying to see any network activity that isn't going through their VPN, I just think I'd be better off safe than sorry. Additionally, are there any steps I can take to limit what this second connection can see and do?

Thank you!

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  • This entirely depends on the configuration of each device on your network. I would like to point out the entire purpose of using a VPN, is to connect your work machine to the virtual private network at your company, in order to separate and isolate the machine from your private intranet. This security goes both ways depending on the configuration of the VPN itself.
    – Ramhound
    Mar 27, 2020 at 16:21

3 Answers 3

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Additionally, are there any steps I can take to limit what this second connection can see and do?

If you had a managed switch, you could set up a VLAN to segregate traffic on a port-basis and even achieve full isolation. Since you mentioned a router you likely don't have this option but have a look at the relevant manual for your model. Maybe there are security features available to you.

As to the question:

how much traffic can that new computer potentially see ?

That depends. I have seen (old) networks with lots of broadcast traffic, due to poor setup, old equipment and other reasons. You can find out for yourself by sniffing the traffic with Wireshark for example. If you don't want to install it on your computer you could boot a live Linux distro such as Kali on a USB stick.

Then, making sense of all the frames captured is probably not going to be easy if you don't have a background in networks, but I find that the education value is great.

References: VLAN Network Segmentation and Security - Chapter 5

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If it is a router and not a hub, the other computer will only see ARP traffic, "WHO IS xxx".

But, you could be at risk for a man in the middle attack with an ARP spoof, where the computer will spoof itself as the router and then traffic from Computer1 will go to Computer2 and then Computer2 will forward the traffic to the router.

But, other than that, the other computer won't see any normal network traffic other than ARP requests or if you ping that device. It will only see traffic addressed to it as most traffic isn't broadcasts to all devices.

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Well-implemented network security in the configuration of your OS and of the network hardware prevents the user of machine A from seeing the traffic of machines B-Z (other than ARP as mentioned in another answer).

If the network hardware and PC OS are not kept up to date or if the publishers/manufacturers don't fix known problems (more), that gives folks with tools such as Kali a chance to see what they should not.

Is your router's firmware up to date? Are you applying all the updates and patches to your OS? Only you can answer those questions

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