4000 Router Series Layer 3 - IP Services Configuration Guide

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Dual Stack Lite (DS-Lite) is a combination of the tunneling and NAT technologies. NAT translates

the private IPv4 addresses of the IPv4 hosts before the hosts reach the IPv4 public network.

DS-Lite tunnel supports only an IPv4 host in a private network initiating communication with an IPv4

host on the Internet. It does not support an IPv4 host on the Internet initiating communication with

an IPv4 host in a private network.

Figure 99 DS-Lite tunnel

As shown in Figure 99, the DS-Lite feature contains the following components:

{ Basic Bridging BroadBand (B4) element

The B4 element is typically a CPE router that connects end hosts. IPv4 packets entering the B4

router are encapsulated into IPv6 packets and sent to the AFTR. IPv6 packets from the AFTR are

de-encapsulated into IPv4 packets and sent to the subscriber's network.

Hosts that can serve as the B4 router are referred to as DS-Lite hosts.

{ Address Family Transition Router (AFTR)

An AFTR resides in the ISP network and terminates the tunnel from the B4 router. NAT is also

implemented on the interface that connects the public IPv4 network.

AFTR de-encapsulates the tunneled packet, translates the network address, and routes the

packet to the destination IPv4 network. For IPv4 packets coming from the public IPv4 network,

AFTR performs reverse address translation and sends them to the B4 router by using the DS-Lite

tunnel.