Steps for determining an optimal range for the EXPLICITBINDPORTRANGE parameter

Determine an optimal range for the EXPLICITBINDPORTRANGE parameter.

Perform the following steps:

1. Change your existing configuration to specify the GLOBALCONFIG EXPLICITBINDPORTRANGE parameter on all stacks that you anticipate will be participating in explicit bind port range processing. As a guideline, the port range size should be at least large enough to allow for 2 blocks of ports to be in use by each participating TCP/IP stack (128 * number of TCP/IP stacks using the explicit bind port range). If you are using an SRCIP block, do not initially make the change to use distributed DVIPAs on the DESTINATION rules.
2. Start all of the stacks, servers and clients to reach the typical steady state connection load for your sysplex environment. All connections from sockets that were explicitly bound to the IPv4 address, INADDR_ANY, or the IPv6 unspecified address (in6addr_any) and port 0 will use ports from the new range.
3. Periodically check to determine how many ports from this new range are in use by issuing a D NET,STATS,TYPE=CFS,STRNAME=EZBEPORTvvtt,LIST=0 command (See Figure 1).
   Figure 1. VTAM® NET,STATS,LIST=0 example

   D NET,STATS,TYPE=CFS,STRNAME=EZBEPORT1121,LIST=0             
   IST097I DISPLAY ACCEPTED                                             
   IST350I DISPLAY TYPE = STATS,TYPE=CFS 180                            
   IST1370I NETA.SSCP1A IS CONNECTED TO STRUCTURE EZBEPORT1121              
   IST1797I STRUCTURE TYPE = LIST                                       
   IST1517I LIST HEADERS = 1024 - LOCK HEADERS = 1024                   
   IST1373I STORAGE ELEMENT SIZE = 256                                  
   IST924I -------------------------------------------------------------
   IST1374I                            CURRENT     MAXIMUM  PERCENT     
   IST1375I STRUCTURE SIZE               8192K      15104K     *NA*     
   IST1376I STORAGE ELEMENTS               128       22400       0      
   IST1377I LIST ENTRIES                     5         700       0      
   IST924I -------------------------------------------------------------
   ISTREW1I EXPLICITBINDPORTRANGE - START: 50000 END: 50255 
   IST1823I LIST DVIPA SYSNAME  TCPNAME                # ASSIGNED PORTS 
   IST1824I    0 EXPLICITBINDPORTRANGE                              192
   IST1825I            VIC015   TCPCS                                64
   IST1825I            VIC021   TCPCS11                             128             
   IST314I END 

4. Check for message EZD1296 which will be issued if local ephemeral ports were used for connections because no explicit bind ports were available from the active EXPLICITBINDPORTRANGE parameter.
5. If message EZD1296 is not issued and if the number of allocated ports is consistently less than the total port range, then proceed to the next step, otherwise:
   1. Change the GLOBALCONFIG EXPLICITBINDPORTRANGE parameter to use a larger explicit bind port range; as a guideline increase the size by at least 64 for each participating stack (64 multiplied by the number of TCP/IP stacks)
   2. Issue a VARY TCPIP,,OBEYFILE command to change the range on each of the stacks and return to step 3 above.
6. Change your SRCIP block to use distributed DVIPAs on DESTINATION rules.