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In computer networking, MTU (Maximum Transmission Unit) is the size (in bytes) of the largest packet that can be transferred by an interface without IP fragmentation. The default interface MTU in OpenStack is 1500 bytes. This means, packets with payloads bigger than 1500 bytes are fragmented into multiple smaller packets each with payload 1500 bytes or smaller. At high packet rate, fragmentation adds additional processing overhead on the interface. This reduces performance when the number of packets is scaled.

Jumbo frames carry huge packets with up to 9000 bytes of payload. The MTU set to enable jumbo frames is 9000 bytes plus any header size. Enabling jumbo frames reduces fragmentation and the processing overhead of interfaces.

This talk explains how to enable jumbo frames in OpenStack Neutron in order to increase scalability and performance at high packet rate. This talk also covers some basic concepts like IP fragmentation and Path MTU Discovery in OpenStack.