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Follow-up work on NAT-PT, 10 October 2007

Document Type IAB Statement
Title Follow-up work on NAT-PT, 10 October 2007
Published 2007-10-10
Metadata last updated 2023-08-09
State Active
Send notices to (None)
    To: The Internet Engineering Steering Group 
    Subject: Follow-up work on NAT-PT
    From: "Olaf M. Kolkman" 
    Date: Wed, 10 Oct 2007 21:34:10 +0200
    Cc: IAB IAB , IETF at

Dear Colleagues,

The IETF has previously standardized NAT-PT as a means of 
intercommunication by packet translation at the Internet layer. However 
subsequent analysis revealed a number of issues with NAT-PT that make it 
a poor choice for a general purpose interconnection mechanism. The IESG 
recently approved RFC 4966 which states:

  Although the [RFC2766] form of packet translation is not generally 
  applicable, it is likely that in some circumstances a node that can
  only support IPv4 will need to communicate with a node that can only
  support IPv6; this needs a translation mechanism of some kind.
  Although this may be better carried out by an application-level proxy
  or transport-layer translator, there may still be scenarios in which
  a revised, possibly restricted version of NAT-PT can be a suitable
  solution; accordingly, this document recommends that the IETF should
  reclassify RFC 2766 from Proposed Standard to Historic status to
  avoid it from being used in inappropriate scenarios while any
  replacement is developed.

As noted in the approved text quoted above, there may still be scenarios 
in which a revised, possibly restricted version of NAT-PT may be 

For example, one such scenario may be increasingly likely given the 
current rate of consumption of IPv4 address space. Namely, there may be 
legacy IPv4-only hosts in one part of the Internet that want to talk to 
dual-stack hosts in another part of the Internet that do not have public 
IPv4 addresses. The servers follow today's recommendation to be dual-
stack, but the scenario still does not work, therefore the general 
recommendation that servers be dual-stack is clearly not sufficient.

Furthermore, classic v4-v4 NAT is also not sufficient for this scenario. 
For example, one cannot put multiple web servers behind the same classic 
v4-v4 NAT since web browsing uses port 80, and the NAT has fewer public 
IP addresses than the number of servers behind it or else the NAT 
wouldn't be needed.

While the IETF has reclassified RFC 2766 as Historic, up to now there 
has been no replacement to RFC 2766 for such scenarios. The IAB note 
that the IESG has now begun discussion on what work is needed for 
transitioning to IPv6 and where it should be done, and the IAB 
encourages the IESG to strongly consider the scenario outlined above 
when chartering IETF work.

-- The IAB