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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. |
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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. |
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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. |
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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 |
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Application Servers |
Runtimes for Java Technology |
Java SDK |
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