CGNAT Integration with Broadband Subscribers Overview

This topic provides an overview of the CGNAT feature, its deployment types, and its benefits.

Carrier-Grade Network Address Translation (CGNAT) enables conservation of IPv4 addresses by enabling multiple subscribers to share a limited pool of public IPv4 addresses. CGNAT is widely deployed in broadband networks to address subscriber growth exceeding public IPv4 availability. Key functionalities include allocating fixed public IPv4 addresses and port blocks per subscriber, using RADIUS accounting updates to report allocations, and advertising public addresses within specific routing instances.

For more information about RADIUS accounting functionality, see RADIUS Accounting Statistics for BNG with CGNATS.

In broadband environments, subscribers receive private IPv4 or IPv6 addresses. CGNAT translates these private addresses to public IPv4 addresses when traffic exits the service provider network. In addition to basic IP address translation, CGNAT uses Network Address and Port Translation (NAPT) for translating source port numbers to dynamic source port numbers within a specified port-block range.

Junos OS supports seamless integration of CGNAT with broadband subscriber management, allowing application of NAT policies and accounting on a per-subscriber basis. When CGNAT integrates with subscriber management:

• NAT behavior aligns with subscriber lifecycle events such as login, logout, and service updates.

• Accounting and reporting generate usage records tied to individual subscribers. Service providers can export these records using syslog or RADIUS accounting based on deployment needs.

Junos OS supports two types of CGNAT deployment methods:

• Inline CGNAT: Processes NAT directly on the subscriber-facing routing device. Subscriber traffic flows through a device hosting both subscriber management and CGNAT functions.

• External CGNAT: Offloads NAT processing to a dedicated CGNAT device. Subscriber-facing devices forward traffic to external CGNAT systems for address translation.