On Windows® when using task offload feature, Load Balancer's NAT and CBR forwarding methods do not work
 Technote (troubleshooting)
 
Problem(Abstract)
On Windows, when using an adapter card that supports task offloading (also referred to as checksum offloading or adapter checksum calculation), Load Balancer's NAT or CBR forwarding methods do not work. To avoid this problem, disable task offload on the adapter card setting.
 
Cause
Task offload, a feature on Windows platforms, allows the TCP checksum to be calculated by the adapter card rather than the operating system. Task offload might improve performance on the system; however, the problem with task offload is that TCP checksum is not computed correctly for packets coming from the cluster address. This is the case with NAT and CBR forwarding methods, where the back-end servers forward packets to the Load Balancer machine before reaching the client.
When task offload is enabled, Load Balancer's advisors indicate all servers as down and reach targets are down. Advisors send traffic from the cluster address, collocated traffic comes from the return address, and reach target traffic comes from the cluster address. The only forwarding method that works when task offload is enabled is the mac-based forwarding method, where the back-end servers forward packets directly to the client.
 
Resolving the problem
Disable task offload on the adapter card settings when using NAT and CBR forwarding methods.
Note: It is unnecessary to disable task offload for the following versions (or higher levels) of Load Balancer:
  • 4.0.3.57
  • 5.0.2.46
  • 5.1.1.25
  • 6.0.1.1

The Load Balancer installation code disables task offload, then reenables it when Load Balancer is uninstalled.
 
 
Cross Reference information
Segment Product Component Platform Version Edition
Application Servers WebSphere Edge Server Load Balancer Windows 2000 Edge Server 2.0 GA, Edge Server 2.0 NLV, Edge Server 2.0.x
Application Servers Runtimes for Java Technology Java SDK
 
 


Document Information


Product categories: Software > Application Servers > Distributed Application & Web Servers > WebSphere Application Server > Edge Component
Operating system(s): Windows
Software version: 5.1.1
Software edition:
Reference #: 1153434
IBM Group: Software Group
Modified date: Sep 3, 2007