Let’s break things down and make it simple what is a black hole? A black hole is a region of spacetime where gravity is so strong that nothing exists. That is what I understood from reading Wikipedia but in networking, what is a black hole and where is it used. In my mind, a black hole means nothing, like literally nothing. I don’t know anything, same with a network. A black hole network is where you put a device on that VLAN (Virtual LAN ), and it cannot connect to anything. Now, why on earth would I do such a thing lets take an example of physical security if I have access to a switch. I can plug my device in and have full access to it in a typical network. Now that is scary, so how do I secure this from a defender point of view? It’s not like I can have a guard guarding the switches 24/7. I wonder how many switch ports he would be able to protect at one time, so that’s where this concept of black hole networking comes up. As soon as a device is connected to the network, it gets put in a separate VLAN. Now in an organisation, you have something a little different based on what kind of security measure you put in place. However, the point is that you put anything untrusted on that network. Let us take an example if an internal employee has just come from a business trip. You don’t know what kind of viruses or malware his laptop might have picked up what access points that employee may have connected to, so what do you do as a network administrator/security admin?
You let him in your network but put him in a separate VLAN where he cannot connect to the company servers. Then you make sure his system has the latest patches, and you do a virus scan on that system only after which he has access to the corporate network.