[arin-ppml] inevitability of NAT?

Scott Helms khelms at zcorum.com
Thu Feb 10 10:53:33 EST 2011

> CGN is a NAT, and is essentially just a higher-scale implementation of the NAT that we all know and "love".  I think you're right to challenge the oft-repeated belief that CGN is somehow fundamentally different.  That being said, the deployment model of CGN is significantly different from CPE-based NAT, and that fact does results in some differences in how it can be used.  The two fundamental differences are fairly obvious: 1) CGN is run by a carrier, and so the subscriber doesn't necessarily have the same degree of control.  2) CGN allows for greater oversubscription of public IP addresses, and so there is potentially a many-to-one relationship between subscribers and public addresses.


    I know the vendors have all thought about the issue of over 
subscription of IP's and logging of translations so you can go back and 
identify who was using a specific IP for a LEA request so over 
subscribing doesn't doesn't bother me as much.  The other issue I didn't 
think of was that the people who are most likely to be attracted to 
CGNAT/LSN are also the networks that are most likely to have CPE NAT at 
or near 100% of their end users.  That creates the likelihood of double 
NAT if they don't change their CPE's, which is very problematic.  DSL 
systems aren't like DOCSIS networks where I know I can change the 
configuration of the premise gear with ease.

Scott Helms
Vice President of Technology
ISP Alliance, Inc. DBA ZCorum
(678) 507-5000

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