Background

As the number of Internet users keeps increasing and mobile broadband and the Internet of Things rapidly develop, IPv4 address shortage has become an increasingly serious problem. IPv6 can solve the problem of IPv4 address shortage, but IPv4 networks will not be replaced by IPv6 networks in a short time because a large number of IPv4 services are deployed on the Internet. A reasonable approach is to gradually deploy IPv6 without affecting existing IPv4 services. When IPv6 is widely used, the IPv4 Internet can be replaced by a pure IPv6 Internet. IPv4 and IPv6 will coexist for a long time before a pure IPv6 Internet is built.

During transition from IPv4 to IPv6, NAT can mitigate IPv4 address shortage. Traditional NAT is deployed on the CPE to translate addresses for a few users. CGN is deployed on the carrier network to translate addresses for a large number of users. Therefore, CGN devices must have higher capacities, performance, and reliability than the traditional NAT devices.

• CGN devices can translate between various network addresses, for example, between IPv4 private addresses, between IPv4 private and public addresses, and between IPv4 addresses and IPv6 addresses. Some CGN devices also provide the tunnel function.

• The CGN function can be provided by an independent CGN device and or a CGN card installed on another device. A CGN card can be installed on a broadband remote access server (BRAS) so that one physical device can provide the BRAS and CGN functions.

• In centralized mode, one or more CGN devices (mostly independent CGN devices) are deployed near or at the core of a metropolitan area network (MAN). This mode applies to the early stage of IPv6 deployment when the number of IPv6 users and traffic volume are small.

• In distributed mode, a large number of CGN devices (mostly CGN cards installed on BRAS devices) are deployed near or at the edge of a MAN. This mode applies to the scenario where the number of IPv6 users and traffic volume is large.

Purpose

CGN translates addresses for a large number of users, so it is also called LSN. If no protection measure is taken, a CGN fault can affect a large number of users. More users are affected in centralized mode than in distributed mode. To enhance reliability of CGN devices, HA can be used to implement backup between CGN cards on a single device or between multiple CGN devices.

Benefits

• Benefits to carriers

  HA improves network reliability and helps carriers quickly deploy CGN devices on IPv4-to-IPv6 networks.

• Benefits to users

  When a fault occurs on a service board, CGN device, or link, services are not interrupted, and users do not even know the fault.