Flannel implements the Container Network Interface (CNI) to enable pod networking in a Kubernetes cluster. Flannel runs a small, single binary agent called flanneld in a Pod on each host, and is responsible for allocating a subnet lease to each host out of a larger, preconfigured address space. Flannel uses the Kubernetes API directly to store the network configuration, the allocated subnets, and any auxiliary data (such as the host's public IP). Packets are forwarded using VXLAN encapsulation.
spec:
flannel:
version: "0.20.0"
podCIDR: "10.32.0.0/22"
podCIDRRange: "/22"
| Flag | Usage |
|---|---|
| version | The version of Flannel to be installed. |
| podCIDR | The subnet used by Pods. |
| podCIDRRange | The size of the subnet used by Pods. |
The following additional ports must be open between nodes for multi-node clusters:
| Protocol | Direction | Port Range | Purpose | Used By |
|---|---|---|---|---|
| UDP | Inbound | 8472 | Flannel VXLAN | All |
| Protocol | Direction | Port Range | Purpose | Used By |
|---|---|---|---|---|
| UDP | Inbound | 8472 | Flannel VXLAN | All |
The Pod subnet will default to 10.32.0.0/20 if available.
If not available, the installer will attempt to find an available range with prefix bits 20 in the 10.32.0.0/16 or 10.0.0.0/8 address spaces.
This can be overridden using the podCIDR to specify a specific address space, or podCIDRRange to specify a different prefix bits.