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.
MTU configuration
CNI, which is used by Kubernetes and the Mesos Unified Containerizer, supports configuring the MTU 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 update workload MTUs, see the section that corresponds to your plugin type.
MTU configuration with CNI
MTU is set in the by the "mtu": <MTU size>
field of the CNI configuration. Example:
{
"name": "any_name",
"cniVersion": "0.1.0",
"type": "calico",
"mtu": 1480,
"ipam": {
"type": "calico-ipam"
}
}
Note: If using Kubernetes self-hosted manifests, you should modify the
veth_mtu
value in the Calico ConfigMap instead, and leave"mtu"
here set to__CNI_MTU__
. See below for more details.
MTU configuration with Kubernetes self-hosted manifests
When using Kubernetes self-hosted manifests, the CNI plugin derives the MTU value
from the veth_mtu
field of the calico-config ConfigMap, and it is set to 1440
by default. On restart of the calico/node
pods, any references to
__CNI_MTU__
are replaced by the veth_mtu
value and inserted into the CNI
configuration file (aka conflist) at the directory specified by Kubernetes
(currently defaults to /etc/cni/net.d/
).
Restarting the calico/node
pods will also update any Calico
tunnel network interfaces on that node. From this point forward, any pods
started will also have the updated MTU value.
Setting tunnel MTU with a 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, Felix derives this value from
the veth_mtu
field of the calico-config ConfigMap, which is set to 1440
by default.
Setting tunnel MTU with calicoctl
To set the IP-in-IP MTU value for all Calico nodes in your cluster, use the following command to retrieve the current Felix settings.
calicoctl get felixconfig --export -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.