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Article ID: 326367 - Last Review: February 27, 2014 - Revision: 2.3

This article was previously published under Q326367
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If you set an Advanced Program-to-Program Communications (APPC) Mode definition's Max Send RU Size or Max Receive RU Size to greater than 32 KB (32,768), the SNA Server service specifies primary and secondary maximum request unit (RU) size values that are not valid in a BIND request (BIND bytes 10 and 11, respectively).

As a result, the SNA Server service issues an SNA UNBIND command to end the session.


The SNA Server service is designed to limit the RU size to 16384 (16 KB) bytes, however, SNA Manager limits the RU size to 65527 bytes (65 KB).

The SNA Server service handles the maximum RU size setting as follows:
  • If the maximum RU size is between 16384 and 32768, the SNA Server service uses an RU size of 16384 bytes.
  • If the maximum RU size is greater than 32768, the SNA Server service uses an invalid value for the RU size because the two-byte signed value overflows.


To prevent this problem from occurring, set maximum send and receive RU size values that are between 256 and 16384.


Microsoft has confirmed that this is a problem in SNA Server 4.0 and Host Integration Server 2000.


The request unit (RU) size values represent the maximum size of the data message that can be sent or received between SNA Server and the Host. If an application has a data request that is larger than the maximum, the SNA Server service breaks this request into multiple blocks to fit each block in the maximum RU size.

IMPORTANT: The minimum RU size on Host Integration Server 2000 is 256. The valid range for Max Send RU Size and Max Receive RU Size is from 256 through 16384; the default is 1024.

The Host Integration Server 2000 Help documentation states that the valid Max Send RU Size and Max Receive RU Size value range is between 256 and 16384. If you use values that are greater than 65 KB (65535), and if you try to save or exit the APPC Mode Properties page, the following error message appears:
Please enter an integer between 256 and 65527
This gives the incorrect impression that the supported values are 256 to 65527.

  • Microsoft SNA Server 4.0
  • Microsoft SNA Server 4.0 Service Pack 1
  • Microsoft SNA Server 4.0 Service Pack 2
  • Microsoft SNA Server 4.0 Service Pack 3
  • Microsoft SNA Server 4.0 Service Pack 4
  • Microsoft Host Integration Server 2000 Standard Edition
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