In the Dual Stack Lite solution, what is the function of the B4 component?
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Dual Stack Lite (DS-Lite) is an IPv6 transition technology that enables service providers to offer IPv6 connectivity to their customers while continuing to support IPv4 connectivity. DS-Lite is a form of IPv6-in-IPv4 tunneling, where IPv6 traffic is encapsulated inside IPv4 packets and tunneled across an IPv4 network. The B4 component is an essential part of the DS-Lite solution and is responsible for handling the IPv4 traffic from the customer premises equipment (CPE) and forwarding the encapsulated IPv6 traffic to the Address Family Transition Router (AFTR) located in the service provider's network.
The B4 component is typically implemented in the CPE, which is the device installed at the customer's premises and connected to the service provider's network. The B4 component performs the following functions:
IPv6 in IPv4 encapsulation: The B4 component encapsulates the customer's IPv6 traffic inside IPv4 packets and forwards them to the AFTR in the service provider's network. This encapsulation enables the transport of IPv6 traffic over the existing IPv4 infrastructure without requiring any changes to the core network.
IPv4 address translation: The B4 component translates the source IPv4 address of the encapsulated IPv6 traffic to a globally routable IPv4 address assigned by the service provider. This translation enables the service provider to manage and route the IPv6 traffic over the IPv4 infrastructure.
Decapsulation of IPv4 packets: When the AFTR receives the encapsulated IPv6 traffic from the B4 component, it strips off the IPv4 header and forwards the original IPv6 packet to its destination. The B4 component performs the reverse process, i.e., it receives the encapsulated IPv4 packets from the AFTR and decapsulates them to extract the original IPv4 packet.
Reversal of Network Address Translation: The B4 component performs a reverse Network Address Translation (NAT) function by mapping the translated IPv4 address back to the original IPv4 address of the customer's CPE. This mapping enables the customer to communicate with other IPv4 hosts on the internet.
In summary, the B4 component in the DS-Lite solution is responsible for encapsulating IPv6 traffic inside IPv4 packets, translating the IPv4 source address, and forwarding the encapsulated traffic to the AFTR in the service provider's network. The B4 component also performs the reverse functions when receiving encapsulated IPv4 packets from the AFTR, thereby enabling the communication between IPv6 and IPv4 hosts.