How Nat Works - Cisco ASR 5000 series Product Overview

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▀ How NAT Works

How NAT Works

The following steps describe how NAT works:

In the subscriber profile received from the AAA Manager, the SessMgr checks for the following:

If all of the above is true, once a private IP address is allocated to the subscriber, the NAT resource to be used for the

subscriber is determined. This is only applicable for not-on-demand allocation mode.

them to get translated: Class A 10.0.0.0 – 10.255.255.255, Class B 172.16.0.0 – 172.31.255.255, and Class C

192.168.0.0 – 192.168.255.255

group from a maximum of three pools/pool groups. Hence, at any point, there can be a maximum of three

NAT IP addresses allocated to a subscriber.

Flow setup is based on the NAT mapping configured for the subscriber:

The following figures illustrate the flow of packets in NAT processing.

▄ Cisco ASR 5000 Series Product Overview

Enhanced Charging Service subsystem must be enabled

In the Firewall-and-NAT policy, NAT must be enabled

The Firewall-and-NAT policy must be valid

For Many-to-One NAT, at least one valid NAT IP pool must be configured in the Firewall-and-NAT

policy, and that NAT IP pool must be configured in the context

The private IP addresses assigned to subscribers must be from the following ranges for

A subscriber can be allocated only one NAT IP address per NAT IP pool/NAT IP pool

In case of one-to-one NAT mapping, the subscriber IP address is mapped to a public IP address. The

private source ports do not change. The SessMgr installs a flow using the NAT IP address and a

fixed port range (1–65535).

In case of many-to-one NAT mapping, a NAT IP address and a port from a port-chunk, are allocated for

each connection originating from the subscriber. In order to identify a particular subscriber call line,

the SessMgr installs a flow using NAT (public) IP address + NAT ports allocated for the subscriber.

Network Address Translation Overview