If you are using TCP/IP to connect XDB Link to OS/390, and you are using a version of DB2 that does not support direct access to the DDF facility via TCP, you must install and configure the XDB Link Host Option on the host. This program receives TCP/IP packets containing DRDA-compliant requests from XDB Link and routes them to DB2 via APPC. If DB2 security is a concern, it is suggested the XDB Link be used in all cases.