Hardware Offload
TCP Segmentation Offload (TSO)
Uses the TCP protocol to send large packets. Uses the NIC to handle segmentation, and then adds the TCP, IP and data link layer protocol headers to each segment.
UDP Fragmentation Offload (UFO)
Uses the UDP protocol to send large packets. Uses the NIC to handle IP fragmentation into MTU sized packets for large UDP datagrams.
Large Receive Offload (LRO)
Uses the TCP protocol. All incoming packets are re-segmented as they are received, reducing the number of segments the system has to process. They can be merged either in the driver or using the NIC. A problem with LRO is that it tends to resegment all incoming packets, often ignoring differences in headers and other information which can cause errors.
It is generally not possible to use LRO when IP forwarding is enabled. LRO in combination with IP forwarding can lead to checksum errors. Forwarding is enabled if /proc/sys/net/ipv4/ip_forward is set to 1.
With mlx5 driver, RFS cannot function if LRO is enabled. See also NIC Scaling and Steering.
Checksum Offload
The driver can indicate to the Linux Networking Stack that the hardware successfully validated the IP and L4 checksum so the Linux Networking Stack does not need to deal with IP/L4 Checksum validation.
Software Offload
Generic Segmentation Offload (GSO)
Uses the TCP or UDP protocol to send large packets. If the NIC cannot handle segmentation/fragmentation, GSO performs the same operations, bypassing the NIC hardware. This is achieved by delaying segmentation until as late as possible, for example, when the packet is processed by the device driver.
Generic Receive Offload (GRO)
Uses either the TCP or UDP protocols. GRO is more rigorous than LRO when resegmenting packets. For example it checks the MAC headers of each packet, which must match, only a limited number of TCP or IP headers can be different, and the TCP timestamps must match. Resegmenting can be handled by either the NIC or the GSO code.