The components of this illustration are as follows:
•
Private IP4 subscribers: It denotes a private network.
•
Interface/VLAN: It denotes a designated interface or VLAN which is associated with the VRF.
•
Inside VRF: It denotes the VRF that handles packets coming from the subscriber network. It is known
as inside VRF as it forwards packets from the private network.
•
App SVI: It denotes an application interface that forwards the data packet to and from the ISM. The data
packet may be sent from another line card through a backplane. Because the ISM card does not have a
physical interface, the APP SVI acts as a logical entry into it.
The inside VRF is bound to an App SVI. There are 2 App SVIs required; one for the inside VRF and
the other one for the outside VRF. Each App SVI pair will be associated with a unique "inside VRF"
and a unique public IP address pool. The VRF consists of a static route for forwarding packets to App
SVI1.
•
Outside VRF: It denotes the VRF that handles packets going out to the public network. It is known as
outside VRF as it forwards packets from the public network.
•
Public IPV4: It denotes a public network.
The following figure illustrates the path of the data packet from a private network to a public network in a
NAT implementation.
The packet goes through the following steps when it travels from the private network to the public network:
Cisco IOS XR Carrier Grade NAT Configuration Guide for the Cisco CRS Router, Release 5.2.x
OL-32659-01 9
Implementing Carrier Grade NAT on Cisco IOS XR Software
Implementing NAT 44 over ISM
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