Often this comes into the subnetting discussion by my friends who are deploying IPv6 for the first time. How do you calculate subnets outside the 4-bit nibble boundary? This also happens to be one of starting points of APNIC IPv6 routing workshop where I occasionally instruct as community trainer. So what is a Nibble boundary? In IPv6 context, it refers to 4 bit and any change in multiple of 4 bits is easy to calculate.