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Translation templates
Introduction
Translation template
24
4.7 Translation templates
Life is easy and nice in case the interface on the public network has a permanently
assigned IP address. However, what to do with public interfaces which have a
dynamically assigned IP address. For example in the case of PPPoA, 50.0.0.1 can
change to 50.0.0.x the next time the dial-up connection is established.
In order to still be able to configure incoming connections for these types of
interfaces, the concept of templates is available.
A template assigns a wildcard (0.0.0.x) to the IP address of the public interface.
When a PPP session is established, the wildcard is replaced by the effectively
dynamically assigned IP address of the PPP interface.
example
`
192.168.0.1
Src IP
Dest IP
50.0.0.200
192.168.0.1
The first entry listed in the address translation table (NAT box Internal Mappings) is
the template we created and is persistently stored. The second one is a temporary
entry which was added to the PPP setup, it is an "instance" of the template. This
instance is now a fully functional static address mapping entry with a lifetime equal
to the lifetime of the PPP connection.
Inside IP
192.168.0.1
192.168.0.1
0.0.0.1: wildcard
NAT enabled
TM
SpeedTouch
192.168.0.254
50.0.0.12
Src port
Dest port
80
5500
Figure 13:
Template example
NAT box Internal Mappings
Outside
Ouside IP
Dest. IP
Inside Port
Port
0.0.0.1
50.0.0.200
5500
2013
50.0.0.12
50.0.0.200
5500
2013
Public
Src IP
Dest IP
Src port
50.0.0.200
50.0.0.12
80
E-NIT-CTC-20040716-0004 v1.0
50.0.0.2
Dest
201
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