What is "tunnel broker"

n. (computer networking) a service which provides a network tunnel

In the context of computer networking, a tunnel broker is a service which provides a network tunnel. These tunnels can provide encapsulated connectivity over existing infrastructure to another infrastructure.

There are a variety of tunnel brokers, including IPv4 tunnel brokers, though most commonly the term is used to refer to an IPv6 tunnel broker as defined in RFC:3053.

IPv6 tunnel brokers typically provide IPv6 tunnels to sites or end users over IPv4. In general, IPv6 tunnel brokers offer so called 'protocol 41' or proto-41 tunnels. These are tunnels where IPv6 is tunneled directly inside IPv4 packets by having the protocol field set to '41' (IPv6) in the IPv4 packet. In the case of IPv4 tunnel brokers IPv4 tunnels are provided to users by encapsulating IPv4 inside IPv6 as defined in RFC:2473.