NetScaler Application Firewall devices are commonly deployed as a cluster of devices behind (hopefully) a NetScaler loadbalancer or Application Delivery Controller (ADC), as we like to call them now. Content Switching or URL based routing decisions are typically done on the load balancer, but some topologies require the flexibility of performing this action from the firewall tier itself. In this case, the firewall is directly connected to the web server tier without a loadbalancer in between.
The NetScaler Application Firewall can do content switching using the AppExpert policy engine based on any incoming request parameters to direct traffic to backend servers. Upgrading to the Platinum edition will make all NetScaler features available in an integrated platform enabling consolidation of server tiers. This feature is available in NetScaler 9.0 Build 69.x onwards as well as the 9.1 release.