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NSX Security Groups and Firewall Rules

As a next-gen firewall, NSX allows us to get very dynamic with our firewall rules and create complex behaviors out of comparably very few rules.  Let's look at the same example 3 Tier Application rule set that I wrote about in my post about the Direction and Applied To fields in NSX Firewall rules post, and look at how these groups could be configured and then we can look at how these rules could be made even more secure.  First though, here's the example rule set:

SourceDestinationActionApplied ToAnyInfraServicesAllowDFWClient DevicesWebAllowWebDB, AppWebDenyWebWebAppAllowAppDB

Direction and Applied To for NSX Firewall Rules

I've had the chance to learn about NSX lately, which has included really diving in to how the firewall behaves.  While it can certainly be used very much like a traditional firewall, you're not doing yourself any favors by doing so.  Remember, this is a policy-based firewall, so our goal is to define as many general behaviors as possible and then have them apply intelligently to the correct VMs based on attributes such as Security Tags.

There's a lot to dig into on this topic, but for now I want to focus on two attributes of a firewall rule: Direction and Applied To.  These two settings can be used to dramatically simplify a firewall configuration and can lead to some unexpected results if not used correctly (also, they took me quite a while to wrap my head around).

The most important thing to remember is that, like all firewalls, NSX eventually boils down to a sequential list of rules.  NSX will do whatever action is specified in the first rule to match a given flow.  Whe…