HI KB article (KB0827799) with details on Discovery and IPv6: Discovery via IPv6 address. Key details in KB:
"Discovery, Service Mapping, Cloud Management, and basically every integration either directly from the instance or via a MID Server, currently needs to use IPv4 addressing. IPv6 is not currently supported.
Discovery will record Internet Protocol version 6 addresses in the CMDB for network interfaces that have them, but Discovery cannot scan devices using those addresses. Any addresses entered in Discovery Schedule and MID Server IP Ranges need to be IPv4."
Discovery over IPv6 ONLY: Currently, setting up discovery ranges subnets only support IPv4 addresses. We have a small, but growing, island of IPv6 ONLY servers that we can ssh to from our mid server over IPv6, but we cannot configure Discovery IP ranges in IPv6. When will Discovery over IPv6 be supported? This is only going to become more and more popular over time.