I do not know IBM’s current practice but in the 1990s acquisitions continued to use their internal networking for quite a long time, just interconnecting the ne

I do not know IBM’s current practice but in the 1990s acquisitions continued to use their internal networking for quite a long time, just interconnecting the networks as necessary and announcing routes internally. 9. addresses only started being used widely inside IBM around 1992 as the internal multi protocol network rolled out (combining RSCS over SNA and TCP/IP). As APPC connected devices gave way to TCP/IP connected devices allocations shot upward, IIRC each major campus was a /16. Advantis/IBM Global Network ran the 9 network on the same physical and logical circuits as the public networks they managed, leading me to bypass the IBM firewall unintentionally multiple times as the filters they used broke. This may be one of the reasons RFC1918 addresses were discouraged (at least through 12/2001 when I left).