Another part of the tunnel broker is obviously the tunnel broker client. To understand what functionality a tunnel broker needs to implement, it is necessary to have a look at the different types of clients that need to be connected to the tunnel broker.

First of all, one needs to identify the network topology that a potential client will most likely reside in. It is assumed that any tunnel broker client only has native global IPv4 connectivity and no global IPv6 connectivity. From a practical viewpoint, having global IPv6 connectivity additionally to the tunnel broker IPv6 connectivity is possible. However, this scenario is not a standard scenario where an IPv6 tunnel broker would be employed. Additionally, effects that are imposed by having two types of global connectivity still need to be investigated. No serious problems are to be expected but tests have not yet been conducted to verify this.

One differentiates between two types of clients that reside in two different network topologies for this particular OpenVPN IPv6 tunnel broker:

• Hermit client: a lone client that will be assigned a /128 address
• Subnet client: a client that will be assigned a /64 prefix and that may act as a router for a subnet where it may announce this /64 prefix to other hosts that use the client as their default router

Figure 5-7 Types of Tunnel Broker Clients