Which method allows dynamic service insertion in Cisco ACI?

Dynamic service insertion in Cisco ACI is primarily facilitated by using a service graph. A service graph allows you to define how services such as firewalls, load balancers, and other network functions are integrated into the network traffic flow. It creates a flexible and dynamic way to insert these services into the path of traffic, allowing changes to be made easily without needing extensive reconfiguration of network devices or reallocation of VLANs.

Service graphs enable multiple services to be chained together through the use of policies and contracts, allowing traffic to be directed to different services based on the requirements of the applications or workloads. This capability is essential for implementing service-oriented architectures and provides agility in responding to changing demands within the data center.

Other options like contracts, bridge domains, and VLANs play important roles in the ACI architecture but do not specifically enable dynamic service insertion. Contracts handle the communication policies between endpoint groups, bridge domains are used for Layer 2 connectivity, and VLANs are associated with traditional network segmentation but do not provide the dynamic and flexible insertion capabilities offered by service graphs.