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Reaching max logons after migrating to z/OS Comm Server V2R2

Question & Answer


Question

We recently migrated up to V2R2 in z/OS comm Server and after that we are We experienced a slow down in IMS when a node reached it's maximum logons. We think the node is trying repeatedly to log on. Is there anything we can do in the VTAM or TCP/IP or IMS definitions to stop the repeated attempts?

Answer

The first thing you want to look at is the VTAM START option: ENHADDR. Someone in your shop may have changed this during the migration process, or you may be using a different VTAM START list. To verify, do a VTAM D NET,VTAMOPTS display. Examine the output and if you have ENHADDR=NO (which happens to be the default), this might be the problem.
See below for a description of ENHADDR: ENHADDR=NO Specifies that you cannot use high-order element addresses for application programs.

 If you specify ENHADDR=NO all element addresses that VTAM obtains for resources in this subarea come out of the 64k element pool. This includes each active (connectable) APPL (two if PARSESS=YES), each activated local LU and PU, and each dynamically defined LU and PU (once connected). We must also obtain a session partner element address for each session in which we are the endpoint or intermediate routing point (unless the session path to that partner is over a FID_4 link - because, in this case, the element address will originate from another subarea's address space). APPN session partner element addresses come out of this subarea's 64K element address pool if you specify ENHADDR=NO. When addresses in the high-order element address pool are available, every SSCP_LU and SSCP_PU element address for DLUR/DLUS, EE line and PU element addresses, and RTP PU element addresses will be allocated from the high-order pool, even if ENHADDR =NO is specified.

ENHADDR=YES Specifies that you can use high-order element addresses for application programs.

 If you specify ENHADDR=YES and have an application program that used the network-qualified address pair control vector X'15', see z/OS Communications Server: New Function Summary.

 SNA PUs have an architected element address pool limit of 64k, however, VTAM has created an additional pool of address spaces whose total is 16348k. In addition, VTAM must still obtain an element address from the 64k pool if the session path, in or out of the host, is over a FID_4 link.

 A SNA network address is in the form of a four byte subarea address and a two byte element address (as in 'ssssssss eeee'), however, only the two low-order bytes of the subarea address are actually used. The mechanism VTAM uses to create and access a different element address space is to use the two high-order bytes as an index field (as in iiiissss eeee). 

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Product Synonym

ZOSCS COMMSERVER

Document Information

Modified date:
17 May 2016

UID

dwa1271428