TSO and LRO

Enabling TCP Segmentation Offload (TSO) and Large Receive Offload (LRO) can improve FortiGate-VM performance by reducing CPU overhead for TCP/IP network operations.

TSO causes network cards to divide larger data chunks into TCP segments. If you disable TSO, the CPU performs segmentation for TCP/IP. TSO is also sometimes called Large Segment Offload (LSO) or Large Send Offload.

LRO reassembles incoming network packets into larger buffers and transfers the resulting larger but fewer packets to the network stack of the host or VM. The CPU has to process fewer packets.

Your server hardware must support TSO and LRO.

To enable TSO from the vSphere web client:

1. Open the Manage tab and select Advanced System Settings.
2. For IPv4 set Net.UseHwTSO to 1 to enable TSO, or to 0 to disable TSO.
3. For IPv6 set useNet.UseHwTSO6 to 1 to enable TSO, or to 0 to disable TSO.

To enable LRO from the vSphere web client:

1. Open the Manage tab and select Advanced System Settings.
2. For IPv4 TSO, set Net.Vmxnet2HwLRO and Net.Vmxnet3HwLRO to 1 to enable LRO, or to 0 to disable LRO.
3. For IPv6 TSO, set useNet.UseHwTSO6 to 1 to enable TSO, or to 0 to disable TSO.