The universal adoption of IPv6 certainly changes how IP addresses are handled compared to IPv4, primarily because each device can have a unique public IP address due to IPv6's vast address space.

However, even in an environment where each device has its own public IP address, routers are still necessary for several important reasons:

1. Routing and Traffic Management

Although each device may have a public IP address with IPv6, the router is still essential for directing data traffic between your local network and the Internet. Routers determine the best route for data to reach its destination, managing the connection between local networks and external networks.

2. Security

With IPv6, although each device can have a public address, this does not eliminate the need for security. Routers can provide essential security features, such as firewalls, that protect internal devices from external attacks. Without a router acting as a barrier, each device would be directly exposed to the Internet, increasing the risk of malicious attacks.

3. Network settings

Routers facilitate the configuration and management of the local network (LAN). They provide DHCPv6 services to assign IP addresses and other necessary network parameters such as DNS and routing options. Additionally, routers allow the implementation of network policies and can manage quality of service (QoS) to prioritize network traffic, ensuring that critical applications have the necessary bandwidth.

4. Support for Mixed IPv4 and IPv6 Networks

As the world transitions to IPv6, many networks still operate using both IPv4 and IPv6 protocols, in what is called “dual stack” operation. Routers are crucial to managing this coexistence, ensuring that devices running different IP versions can communicate effectively.

5. Connecting Multiple Devices

Routers allow you to connect multiple devices to a single Internet source, distributing Internet traffic between them. They also make it easier to create wireless networks (Wi-Fi), extending connectivity beyond what a simple modem could offer.

6. Network Isolation and Segmentation

Additionally, routers allow a network to be segmented into multiple subnets, which can be useful for logically organizing the network, improving performance, and increasing security by limiting the range of network transmissions.

In short, while IPv6 makes it easier for every device to have a public IP address, routers remain essential to ensure efficient, secure and practical network management.

These devices not only provide connectivity, but also a crucial layer of network security and management that is vital for the optimal functioning of any modern IT infrastructure.