The Ethernet MTU

The MTU of an Ethernet frame is a configurable attribute in StarlingX. Changing its default size must be done in coordination with other network elements on the Ethernet link.

In the context of StarlingX, the MTU refers to the largest possible payload on the Ethernet frame on a particular network link. The payload is enclosed by the Ethernet header (14 bytes) and the CRC (4 bytes), resulting in an Ethernet frame that is 18 bytes longer than the MTU size.

The original IEEE 802.3 specification defines a valid standard Ethernet frame size to be from 64 to 1518 bytes, accommodating payloads ranging in size from 46 to 1500 bytes. Ethernet frames with a payload larger than 1500 bytes are considered to be jumbo frames.

For a VLAN network, the frame also includes a 4-byte VLAN ID header, resulting in a frame size 22 bytes longer than the MTU size.

In StarlingX, you can configure the MTU size for the following interfaces and networks:

• The management, cluster host and OAM network interfaces on the controller. The MTU size for these interfaces is set during initial installation.

• Additional interfaces configured for container workload connectivity to external networks,

In all cases, the default MTU size is 1500. The minimum value is 576, and the maximum is 9216.