code: public static IPv6Network fromTwoAddresses(IPv6Address one, IPv6Address two)
      {
          final IPv6NetworkMask longestPrefixLength = IPv6NetworkMask.fromPrefixLength(IPv6NetworkHelpers.longestPrefixLength(one, two));
          return new IPv6Network(one.maskWithNetworkMask(longestPrefixLength), longestPrefixLength);
      }
docs: Create an IPv6 network from the two addresses within the network. This will construct the smallest possible network ("longest prefix
  length") which contains both addresses.
  
  @param one address one
  @param two address two, should be bigger than address one
  @return ipv6 network