Are you talking about the FreeRTOS+TCP Labs project that supports IPv6? If so it is an upgrade of the extensively documented existing but IPv4 only stack. The labs project will eventually become the mainline version, but at the moment the only info is here: https://www.freertos.org/FreeRTOS-Plus/FreeRTOS_Plus_TCP/IPv6/index.html That page provide some info on the differences as far as what is available in the IPv6 version that is not available in the IPv4 version.