Cisco Cisco Packet Data Gateway (PDG) Fehlerbehebungsanleitung
Network Address Translation Overview
▀ How NAT Works
▄ Cisco ASR 5000 Series Network Address Translation Administration Guide
OL-22992-01
How NAT Works
The following steps describe how NAT works:
Step 1
In the subscriber profile received from the AAA Manager, the SessMgr checks for the following:
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
Step 2
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.
subscriber is determined. This is only applicable for not-on-demand allocation mode.
Important:
The private IP addresses assigned to subscribers must be from the following ranges for 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
192.168.255.255
Important:
A subscriber can be allocated only one NAT IP address per NAT IP pool/NAT IP pool 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.
to a subscriber.
Step 3
Flow setup is based on the NAT mapping configured for the subscriber:
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).
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.
installs a flow using NAT (public) IP address + NAT ports allocated for the subscriber.
The following figures illustrate the flow of packets in NAT processing.