Dec 19, 2011

Dual-Stack Lite (DS-Lite)

DS-Lite is a key technology that allows service providers to handle IPv4 address exhaustion incrementally while using IPv6 as a transport layer for IPv4 in the access network.  DS-Lite allows service providers to handle IPv4 address exhaustion by supporting the deployment of IPv6, and at the same time keeping only one layer of NAT for their subscribers.

Because of  IPv4 address exhaustionDual-Stack Lite was designed to let an Internet service provider omit the deployment of any IPv4 address to the customer's Customer-premises equipment (CPE). Instead, only global IPv6 addresses are provided. (Regular Dual-Stack deploys global addresses for both IPv4 and IPv6.)
The CPE distributes private IPv4 addresses for the LAN clients, the same as a NAT device. The subnet information is arbitrarily chosen by the customer, identically to the NAT model. However, instead of performing the NAT itself, the CPE encapsulates the IPv4 packet inside an IPv6 packet. The CPE uses its global IPv6 connection to deliver the packet to the ISP's Carrier Grade NAT (CGN), which has a global IPv4 address. The IPv6 packet is decapsulated, restoring the original IPv4 packet. NAT is performed upon the IPv4 packet and is routed to the public IPv4 Internet. The CGN uniquely identifies traffic flows by recording the CPE public IPv6 address, the private IPv4 address, and TCP or UDP port number as a session.


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