FreeRTOS+TCP is currently an IPv4 TCP/IP stack, but
IPv6 functionality along with support for
multiple network Interfaces is available as a FreeRTOS Labs project. The IPv6/Multi-interface version is fully functional but still undergoing optimization, test coverage and documentation improvements, and memory safety checks. Until that work is complete the code is available on a branch of the
FreeRTOS+TCP GitHub repo separately from the main FreeRTOS downloads.