You have to use following private IPv4 network address ranges:
|24-bit block|10.0.0.0/8|10.0.0.0 – 10.255.255.255|16777216|Single Class A.|
|20-bit block|172.16.0.0/12|172.16.0.0 – 172.31.255.255|1048576|Contiguous range of 16 Class B blocks.|
|16-bit block|192.168.0.0/16|192.168.0.0 – 192.168.255.255|65536|Contiguous range of 256 Class C blocks.|
Same info also here:
[Edge drivers] Private addresses (LAN) - Developer Programs / Writing Edge Drivers - SmartThings Community