The NSX Distributed Firewall provides microsegmentation capabilities by inspecting and controlling traffic at the VM network interface. Unlike a traditional firewall, this allows control of network traffic between workloads on the same network segment, as well as from other sources.

The Distributed Firewall can be configured using a variety of rule types, from traditional rules to dynamic groups that allow policies to be applied based on tags, VM names, or other workload properties. Rules can also be applied to specific objects allowing for scoped policies, including default rules that only apply to specific VMs. Limiting traffic between VMs makes it much harder for attackers to move laterally, and the flexibility of rule definitions mean that rules can be very specific but also easily updated when environments change.

Ideas to consider:

  • The Distributed Firewall is IP-based, so dynamic objects are translated into IP addresses, using the IP addresses detected by VMware Tools or through traffic snooping. Dynamic membership cannot be “Applied To” IP addresses.
  • Much as with traditional firewalls, the complexity and scope of rules impacts performance as each packet is evaluated against each rule, though the Distributed Firewall can take advantage of additional CPU as clusters scale out. It is recommended that rules be limited in scope, such as to a particular network segment, and global rules be considered carefully before implementing.
  • Where possible use groups to define rules, so that changes are easier and updates less susceptible to human error. Create nested groups to aggregate similar rules. For example, rather than having one group for all cloud administrators, consider creating a group for each cloud administrator, then aggregating that into a “supergroup.” If an administrator leaves your organization it is easier to find and remove their access group.
  • Consider defining and documenting a naming strategy for groups so that similar items are grouped together, and data is sortable and easily filtered.
  • Consider defining and documenting a firewalling strategy, such as default allow, default deny, or a documented combination using “Applied To.” Do the same for rules, such as per-application or per-service, so that there is consistency.
  • Enable and implement Distributed Firewalling, so that workloads must have specific distributed firewall rules at all times. Limit generic rules implemented at the gateways.
  • Restrict outbound traffic using DFW to meet the standard approach of blocking traffic closest to the source.
  • Apply IDS/IPS to outbound connections to look for known Command & Control access and common attack signatures.
  • Consider using a proxy server for filtering & inspecting web traffic if virtual desktops are being hosted in the SDDC. Using this model, Internet access would be blocked for endpoints, and only the proxy would be permitted to access the Internet, providing additional URL filtering based on real-time updated lists and/or other identifying capabilities such as geo-location, site categorization, etc.
  • NSX L7 firewall from the Advanced Security add-on can be used to ensure SSL/TLS connections are using encryption methods that meet minimum standards to avoid known attack vectors.

Restrict DNS traffic destined for Internet-based DNS servers and require all workloads to use internal DNS servers that are managed and patched. Log all queries and block or check for requests of known C&C or malicious domains using lists that are updated frequently.