MAP (Mapping of Address and Port)¶
MAP is short for Mapping of Address and Port. It is an IPv6 transition mechanism which enables carriers to transport IPv4 traffic across IPv6 networks efficiently. There are two MAP implementations in TNSR: MAP-T which uses translation and MAP-E which uses encapsulation.
With MAP, IPv4 requests are forwarded from an end user Customer Edge (CE) device through an IPv6 Border Relay (BR) router which processes and forwards the requests to IPv4 destinations. Customer IPv6 requests can can proceed directly to IPv6 destinations without going through the BR, which lowers the burden on the BR.
MAP is stateless, thus capable of handling large scale traffic volume without additional overhead for tracking individual connections. Each CE device receives a public IPv4 address but may only use a specific port range on that address. In this way, multiple users may share a public address without an additional layer of NAT. Since this relationship is predetermined, the ports are also available bidirectionally, which is not possible with other solutions such as Carrier-Grade NAT/NAT444.
MAP-T and MAP-E require port information to operate, thus fragments must be reassembled at the BR before forwarding. This is due to the fact that protocol and port information are only present in the first packet. Intelligent caching & forwarding may be employed for handling fragments.
TNSR can currently act as a BR, providing service to CE clients.
With MAP-T, translations are made using mapping rules that can calculate addresses and ports based on information embedded an in IPv6 address, along with several known parameters.
MAP-T clients determine where to send translated IPv4 traffic using the Default Mapping Rule (DMR) IPv6 /64 prefix.
MAP-E is similar to MAP-T, but instead of translating IPv4 traffic and encoding information in the address, the IPv4 requests are encapsulated in IPv6 between the CE and BR as described in RFC 2473.
MAP-E clients send all IPv4 encapsulated traffic to the BR IPv6 address.
Additional MAP Reading and Tools¶
MAP is a complex topic and much of it is outside the scope of TNSR documentation. There are a number of additional resources that have information on MAP along with examples for other operating systems and example environments.
We recommend the following links as starting points for MAP information.