Configuring MTU

Depending on the environment Calico is being deployed into it may be helpful or even necessary to configure the MTU of the veth (or TAP) that is attached to each workload and the tunnel devices if IP-in-IP is enabled.

Selecting MTU size

Typically the MTU for your workload interfaces should match the network MTU. If you need IP-in-IP then the MTU size for both the workload and tunnel interfaces should be 20 bytes less than the network MTU for your network. This is due to the extra 20 byte header that the tunnel will add to each packet.

Common MTU sizes

Network MTU Calico MTU Calico MTU with IP-in-IP Calico MTU with VXLAN (IPv4)
1500 1500 1480 1450
9000 9000 8980 8950
1460 (GCE) 1460 1440 1410
9001 (AWS Jumbo) 9001 8981 8951
1450 (OpenStack VXLAN) 1450 1430 1400

Default MTU sizes

The default MTU for workload interfaces is 1500, this is to match the most common network MTU size. The default MTU for the IP-in-IP tunnel device is 1440 to match the value needed in GCE.

Using flannel for Networking

When using flannel for networking, the MTU for the network interfaces should match the MTU of the flannel interface. In the above table the 4th column “Calico MTU with VXLAN” is the expected MTU when using flannel configured with VXLAN.

Setting MTU for workload network interfaces

It is the job of the network plugin to create new workload interfaces. The CNI plugin, which is used by Kubernetes, supports configuring the MTU of the workload interface through the CNI configuration file.

The user will also want to configure Calico’s IP-in-IP interface MTU when IP-in-IP is enabled on the cluster. Refer to the MTU table at the top of the page to choose the value that matches your environment.

Note: The MTU on existing workloads will not be updated with these changes. To have all workloads use the new MTU, they must be restarted.

MTU configuration with CNI

To set the MTU when using CNI the line "mtu": <MTU size> must be added to the CNI configuration file.

Example CNI configuration

    "name": "any_name",
    "cniVersion": "0.1.0",
    "type": "calico",
    "mtu": 1480,
    "ipam": {
        "type": "calico-ipam"

When using the Kubernetes self-hosted manifests, the CNI plugin derives this value from the veth_mtu field of the calico-config ConfigMap and is set to 1440 by default.

Setting MTU for tunnel network interfaces

If IP-in-IP is enabled and the MTU needs to be modifed then this must be configured by setting a Felix environment variable or using calicoctl to set the proper configuration variable. Felix will set the tunnel interfaces to the specified MTU.

Setting tunnel MTU through Felix Environment variable

Passing in the environment variable FELIX_IPINIPMTU when running the calico/node container will set the MTU for Felix to use.

When using the Kubernetes self-hosted manifests, the Felix derives this value from the veth_mtu field of the calico-config ConfigMap and is set to 1440 by default.

Setting the tunnel MTU with calicoctl

To set the IP-in-IP MTU value for all Calico nodes in your cluster, use the following command to set the global config value.

# Get the current Felix settings
$ calicoctl get felixconfig -o yaml > felix.yaml

# Modify ipipMTU to the intended integer value
$ vim felix.yaml

# Replace the current felixconfig settings
$ calicoctl replace -f felix.yaml

Note: Setting the ipipMTU config option will result in an immediate update of the tunnel interface MTU on all of the active nodes in your cluster.

Configuring MTU in Kubernetes self-hosted manifests

When using self-hosted manifests with Kubernetes, the MTU should be set by updating the Calico manifest, applying the manifest with those changes, and then restarting each of the calico-node pods.