HP-UX IPv6 Porting Guide (February 2007)

Verifying IPv6 Installation
Chapter 1454
APIs.
if ((fd = open("dev/ip6", O_RDWR)) == -1)
/*
* /dev/ip6 failed to open., Therefore the IPv6 product
*is not installed on the system. An application should use the
* existing IPv4 code.
*/
...
else
/*
* dev/ip6 exists, so the IPv6 product is probably installed.
* IPv6 APIs can handle both IPv4 and IPv6 traffic */
NOTE Starting with HP-UX 11i v2, IPv6 is automatically included in HP-UX.