IBM Support

How to Temporarily Enable or Disable Large Send Offload (LSO) on the IBM i



This technical document describes how to  temporarily enable or disable LSO on IBM i Ethernet resources.


A hosted partition may experience communication problems when delivering frames to a Virtual Input/Output Server (VIOS) Shared Ethernet Adapter (SEA). The VIOS SEA may discard frames that it receives when large send offload is enabled. The following problems have been seen when large send offload is enabled on virtual ethernet resources:

1. Discarded IP Packets

2. Retransmitted TCP Segments

3. Performance Problems On TCP Connections

4. TCP Connections Terminated Prematurely

A support representative may request that large send offload be disabled to help with problem determination.

Resolving The Problem

Disabling large send offload on virtual ethernet resources that deliver frames to SEA's can at times stabilize TCP/IP connections. For more information about the specific steps required to disable large send offload on IBM i ethernet resources, please refer to the video below:

Please note that disabling Large Send Offload (LSO) is only a temporary measure.  It will be re-enabled automatically during an IPL.  This method of disabling LSO is only intended to provide support with an indication of whether an issue may be caused by LSO being enabled. 
In most cases, the cause of the issue is because of a defect or mis-configuration in the Virtual I/O Server (VIOS) and we recommend that if disabling LSO on the IBM i prevents the issues described above from occurring, that a ticket with your VIOS support provider is raised.  There is currently no method of permanently disabling LSO on the IBM i client partition.

[{"Type":"MASTER","Line of Business":{"code":"LOB08","label":"Cognitive Systems"},"Business Unit":{"code":"BU054","label":"Systems w\/TPS"},"Product":{"code":"SWG60","label":"IBM i"},"Platform":[{"code":"PF012","label":"IBM i"}],"Version":"7.1.0"}]

Document Information

Modified date:
22 January 2021