Both FWaaS and Security Groups govern network traffic, but they serve different primary functions and scopes.

• Scope level: Security groups apply security policies at the VM instance level or VM port level. In contrast, FWaaS specifies security policies at the network or router port level.
• Rule capabilities: Security groups do not enable administrators and tenants to explicitly deny specific traffic, whereas FWaaS does provide this capability.

For a layered defense strategy, use FWaaS for north-south perimeter control and security groups for east-west microsegmentation.