When an OSA is configured with a DEVICE and LINK definition, the z/OS® TCP/IP stack has only one connection to the OSA-Express feature. You define this connection with a combination of the DEVICE, LINK, and HOME statements for IPv4, an INTERFACE statement for IPv6, or both. This single connection uses one channel unit address for communication, which is assigned by VTAM® from the DATAPATH parameter of the TRLE definition that represents this OSA-Express feature. Both IPv4 and IPv6 traffic share this one connection and channel unit address. For an overview of the OSA-Express feature and QDIO mode, and how to configure VTAM to use the OSA-Express feature in this mode, see z/OS Communications Server: SNA Network Implementation Guide.
When you configure an OSA-Express feature for IPv4 using the INTERFACE statement and also configure the same OSA-Express feature for IPv6, then the z/OS TCP/IP stack has two connections to the OSA-Express feature and requires two DATAPATH devices.