IP Services: Check the values specified for TCP related configuration statements.

Description: As of z/OS V2R1 the default values for TCPRCVBUFRSIZE and TCPSENDBUFRSIZE parameters on the TCPCONFIG statement have been increased from 16K to 64K. Increasing the receive or send buffer size does not in itself allocate or consume any additional storage. The receive and send buffer sizes determine the amount of data that can be buffered by TCPIP for the application. The increase in the default values can allow more data to be buffered and consequently, more storage to be used.

The default value for the SOMAXCONN statement has increased from 10 to 1024. The SOMAXCONN value limits what a server application can specify for its listening backlog.

The amount of time a connection remains in FINWAIT2 has been changed to use the value specified on the TCPCONFIG parameter FINWAIT2. Previously, an additional seventy five seconds was added to the time specified on the FINWAIT2 parameter before the connection was dropped.

Element or feature:

z/OS Communications Server.

When change was introduced:

z/OS V2R1.

Applies to migration from:

z/OS V1R13 and z/OS V1R12.

Timing:

Before the first IPL of z/OS V2R1.

Is the migration action required?

Yes, for one of the following conditions:

If the potential increase in the size of the send and receive buffers is likely to cause a storage shortage
If you used the current defaulted value of SOMAXCONN to limit applications from specifying a listening backlog larger than 10
If you require the additional seventy-five seconds before the connection is dropped

Target system hardware requirements:

None.

Target system software requirements:

None.

Other system (coexistence or fallback) requirements:

None.

Restrictions:

None.

System impacts:

None.

Related IBM Health Checker for z/OS check:

None.

Steps to take: If needed, do the following:

Change the TCPRCVBUFRSIZE and TCPSENDBUFRSIZE values to 16K.
Change the SOMAXCONN value to 10.
Increase the FINWAIT2 value by 75 seconds.

Reference information: For more information on configuration statements in z/OS Communications Server, see z/OS V2R1.0 Communications Server: IP Configuration Reference.