Appendix A. Deployment Considerations

A.1. AFTR Service Distribution and Horizontal Scaling

One of the key benefits of the Dual-Stack Lite technology lies in the fact that it is a tunnel-based solution. As such, tunnel endpoints can be anywhere in the service provider network.

Using the DHCPv6 tunnel endpoint option [RFC6334], service providers can create groups of users sharing the same AFTR. Those groups can be merged or divided at will. This leads to a horizontally scaled solution, where more capacity is added with more AFTRs. As those groups of users can evolve over time, it is best to make sure that AFTRs do not require per-user configuration in order to provide service.

A.2. Horizontal Scaling

A service provider can start using just a few centralized AFTRs. Later, when more capacity is needed, more AFTRs can be added and pushed closer to the edges of the access network.

A.3. High Availability

An important element in the design of the Dual-Stack Lite technology is the simplicity of implementation on the customer side. An IP4-in-IPv6 tunnel and a default route over it in the B4 element are all that is needed to get IPv4 connectivity. It is assumed that high availability is the responsibility of the service provider, not the customer devices implementing Dual-Stack Lite. As such, a single IPv6 address of the tunnel endpoint is provided in the DHCPv6 option defined in [RFC6334]. Specific means to achieve high availability on the service provider side are outside the scope of this specification.

A.4. Logging

DS-Lite AFTR implementation should offer the functionality to log NAT binding creations or other ways to keep track of the ports/IP addresses used by customers. This is both to support troubleshooting, which is very important to service providers trying to figure out why something may not be working, and to meet region-specific requirements for responding to legally binding requests for information from law enforcement authorities.