CGNAT - Carrier Grade Network Address Translation - NAT

Please explain the technology carrier grade network address translation, aka “CGNAT”. I would like to have an example with a complete configuration in ISP’s provider edge router. CGNAT is used for efficient use of IPv4 address by ISPs. Customers will have a private IP address as their WAN IP and that IP is translated in the ISP’s router to a public IP address and routed to the internet. Please explain this technology. Thank in advance.

Hello Tharmeswaran

Carrier grade NAT is a technology that allows the NAT functionality to occur within the carrier’s network rather than at the customer premises equipment. Traditionally, you have an ADSL or Cable router (or other CPE technology) at the customer’s premises which performs NAT, providing multiple internal private addresses with access to the Internet via a single external public address.

Carrier grade NAT moves the NAT functionality from the customers to a centralised device or set of devices that perform NAT for all the ISP’s customers. This allows for the sharing of small pools of public addresses among many end sites.

The purpose of this is to help mitigate IPv4 address space exhaustion.

Carrier Grade NAT is supported by Cisco devices, and a detailed explanation of the feature and its implementation can be found at the following Cisco documentation:

I hope this has been helpful!