Under a hierarchical IPv6 network, as with any Internet protocol, the ISP (Internet Service Provider) has the ability to see a certain amount of information about your Internet traffic, but there are several nuances to consider to understand exactly what and how can they see it.

What can the ISP see?

1. IP Addresses and Traffic: The ISP can see the IPv6 addresses assigned to your devices and where your data packets are going. This includes the source and destination IP addresses of your Internet connections.
2. Connection Metadata: The ISP can see the metadata associated with your traffic, such as connection times, the amount of data transferred, and possibly the types of traffic if it is not encrypted. They can determine, for example, whether you are streaming video, downloading large files, or browsing the web.
3. Unencrypted Content: If data traffic is not encrypted, the ISP could potentially see the content of what you are sending or receiving. This could include websites visited, messages sent, and other data transmitted.

Limitations on what the ISP can see

1. Encryption: Many of your online activities, such as visiting websites, banking, or sending emails, are protected by encryption (e.g. HTTPS). Encryption hides the content of your data traffic, meaning that although the ISP can see which servers you are connecting to, they cannot see the specific content of what you are viewing or sending.
2. VPN (Virtual Private Network): If you use a VPN, your Internet traffic is sent through an encrypted tunnel, hiding both the content and the final destination of your traffic from your ISP. The ISP will only be able to see that you are connected to the VPN, but will not be able to see beyond that.
3. Privacy Technologies: Using technologies like Tor or privacy-focused browsers can also hide your online activity from your ISP.

IPv6 and Privacy

• Temporary IPv6 Addresses: IPv6 includes a feature called “temporary addresses” that are used for privacy (Privacy Extensions). These addresses change periodically, making it difficult to track a user's online activity based on their IP address.
• Address Breadth: The large number of addresses available in IPv6 further complicates direct monitoring, although this does not prevent ISPs from monitoring at the network level.

In short, although the ISP has the technical ability to see some information about your Internet traffic under IPv6, the extent of exactly what they can see depends largely on whether you are using encryption, VPNs, or privacy technologies.

These tools can protect your privacy and hide your online activities from prying eyes.