HP FlexNetwork MSR2003 Configuration Manual page 303

Figure 119 DS-Lite tunnel
As shown in Figure 119, 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 act 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.
An 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, the AFTR performs reverse address translation and sends them to the B4 router
by using the DS-Lite tunnel.
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