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Follow-up work on NAT-PT

2007-10-10 12:51:14


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 appropriate.

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



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