VLAN/Subnet Security
A Broadcast Domain, a Subnet, a VLAN, 192.168.1.0/24 - you don’t need to explain it for some, but some forget the basiscs and expect a product that can solve anything.
VLAN/Subnet Security is not difficult - probably if I think of VMware NSX Microsegmentation (and btw you don’t need to run overlay networks with NSX). Otherwise it seems “more” difficult, differs from size to size or the number of VLANs. But hey let’s forget Technology for a while, at the end you need to make it more secure, so do it!
Analogy: Think of it like a subnet is a house. Within a house you have different rooms and people can be in different rooms (close doors). If somebody rings the bells and say “somebody at home”, people open the door and speak to other. Or you scream a specific name, the specific name open the open and they speak… if members of the house finds a service that is interessting they wants to speak like you cook and the people get to the kitchen because it smells good … you got the idea. That means, you can close your door, but as soon as you ask, go or look for something, you are using your house - you can not really stop it moving people around the house if you need to use to natural needs.
So, what is the difference if you have Security within you house in place? You make rules: If somebody says “Someboday at home” just a single person noboday will answer that. If there is a speaking ring tone, you will open the door. if the kids wants to play with each other, you allow child 1 and play with child 2 but just in room 1 or the most practical way which mostly works when you come back to the reality. Do members needs to speak to each other? No, just using the house - isolated and everybody can leave the house to communicates to neighbors or what outside services that are necessary.
Why do i stress that topic? In most cases - a Client within a Subnet normally just speak to the Gateway to reach central Services (Active Directory, DNS, Exchange, etc.) or to each the Internet/Cloud Services. There are more situations and it does not matter (right now) how you size your subnet. There are million reasons how you structure your network, structure ip addresses, or structure your datacenter.
Security for that / EVERY Subnet matter. Why? A Metasploit Attack is using Layer 2 (= MAC Address / Switching) and (most) Ransomware are uying Layer 3 (IP Addresses), as long as you request IP Addresses within the same subnet it will not leave the subnet = can communicate to each other.
Using the example of the Software Defined Datacenter:
VMware is using the Definition of a Management Cluster and a Compute Cluster (which are Areas in a context of a Security Zoning Concept). The Management Cluster is build on the Management Plane = vCenter and the Data Plane = ESXi / Hypervisor. It is very important that you place the vCenter is a different subnet than the ESXis to be able to control the traffic between these Zones. Why? The vCenter is a virtual appliance, but is a part of VLAN/Subnet, that is configured through the physical network infrastructure. The ESXi Farm is using IP addresses of a VLAN/Subnet, also managed by physical infrastructure - anything else on top of that infrastructure could be managed by virtual networks and can use software logic to manage security.
VLAN/Subnet Security is based on Networking and how communication is handled within a VLAN/Subnet. These principles are the core elements to start building your infrastructure.
Action:
- Management - ESXi Traffic (VLAN/Subnet) needs to be controlled by a Firewall. Access to the Management, who is eligable in what form to access the management layer? How is the Management Plane using the Data Plane?
- ESXi Servers are the only participants in a ESXi VLAN/Subnet ? as ESXi Servers has their Firewall and they can be configured to manage the traffic between each others anythis else on top, e.g. PVLAN will not make the VLAN/Subnet more secure)
This might interest you:
Virtual Networks follow the same principles but more options to be managed, e.g. Firewall Rules based on Objects (not IP addresses) within the VLAN/Subnet, which gives you flexibility, can follow Zero Trust guidelines and are the basics to build Automation.
BTW: Even if thing your are using already object based firewall rules, it is just a definiton and at the end the system is using IP Addresses. What if you are changing the IP? What if you are delete or move the system?
Links:
You should use the VMware Validated Designs to understand the principles how to design a Software Defined Datacenter and use Hardening Guides to harden the communication for that.