RE: Client Access performance

["Shaw, David" <dshaw@xxxxxxxxxxx>]

Mark,

There's an IBM document that talks about adjusting the Maximum Transmission Unit
to improve throughput and response.  I found it on the web somewhere, but
misplaced the URL.  Here's the text:
-------------------------------
Change the default for the Maximum Transmission Unit 

Currently the AS/400 system defaults to a Maximum Transmission Unit (MTU) of 576
when you add a route to the configuration (through CFGTCP option 2 or
ADDTCPRTE). This value ensures packets will not be dropped over this route
because all TCP/IP implementations have to support at least a 576-byte
transmission unit. 

In many cases, however, this value is unnecessarily small because this route
will only be used on this Ethernet or token-ring, and there are no intermediate
hops that only support a 576-byte packet. If this is the case, you should change
the Route Maximum Transmission Unit size to *IFC. This will change the MTU on
the Route to the Interface MTU size which defaults to the Line Description Frame
Size. This defaults to approximately 2000 for token-ring and 1500 for Ethernet.
There are also cases where the 576-byte size can cause adapter overruns that put
TCP/IP in retransmit mode and slow things down considerably. 

This change often results in a considerable increase in your throughput over
TCP/IP, especially when running network drives, or installing products. 

To change the default used for the MTU: 

On the AS/400 command line type: 
CFGTCP 

Press the Enter key. 

Select Option 2 to work with TCP/IP Routes. 

Position the cursor in the Opt column to the left of the route and type 2. Press
the Enter key. The Change TCP/IP Route screen appears.

Type *IFC in the Maximum transmission unit field. 
Press the Enter key to make the change. 

-----------------

Dave Shaw
Spartan International, Inc.
Spartanburg, SC
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