What term is used for services that provide IPv6 connectivity over IPv4 networks?

Tunnel brokers are services that facilitate the use of IPv6 over existing IPv4 infrastructure. Since IPv4 and IPv6 are not directly compatible, tunnel brokers create a virtual "tunnel" that encapsulates IPv6 packets within IPv4 packets. This allows IPv6 traffic to be transmitted over an IPv4 network, enabling users and organizations that have not yet transitioned to IPv6 to access IPv6 resources.

Tunnel brokers effectively help bridge the gap between the two protocol versions, allowing the gradual adoption of IPv6 while still using the prevalent IPv4 systems. They typically provide IPv6 addresses to clients and handle the encapsulation and decapsulation of packets, making it easier for users to connect to IPv6-enabled networks without needing to overhaul their current IPv4 setups.