Flannel use plugin that focuses on overlay network connectivity. It assigns a subnet to each node and encapsulates traffic between pods using various backend options like VXLAN, Host-GW, or other tunneling protocols.

Kubernetes leverages the Container Storage Interface (CSI) plugin to allocate IP addresses to pods. Each CSI plugin is responsible for managing IP address assignment and ensuring uniqueness within its network segment

Kubernetes leverages the Container Network Interface (CNI) plugin to allocate IP addresses to pods. Each CNI plugin is responsible for managing IP address assignment and ensuring uniqueness within its network segment

Istio, an open-source service mesh platform, directly manage IP address allocation. It delegates IP address management to the underlying networking infrastructure and the orchestration platform, such as Kubernetes.

IP address allocation is handled by the kube-proxy component, which assigns IP addresses based on pod specifications defined in the Kubernetes API. It ensures uniqueness by using a centralized IP address registry