Re: Modified IPv6 to unmodified IPv4

[james woodyatt <jhw@apple.com>]

On Oct 22, 2007, at 01:53, Iljitsch van Beijnum wrote:
> If 1. is out this basically leaves either modifying IPv4 hosts so  
> they can talk to unmodified IPv6 hosts, or modifying IPv6 hosts so  
> they can talk to unmodified IPv4 hosts. The former has the  
> advantage that it keeps IPv6 clean, the latter is more pragmatic  
> because a good part of the IPv4 installed base is presumably  
> unupgradable.

There is one significant way that unmodified IPv4 applications will  
never be able to manage communicating with IPv6-only peers, i.e. when  
their peers store their translated IPv6 addresses in some persistent  
storage, like a logfile or a web page or a report or anything  
generally intended for offline automated analysis, and the IPv4-only  
application needs to do that and finds that it can't cope with its  
address being translated out of the IPv4 address family.

The reverse of this is not a problem.  IPv4-only applications need to  
be upgraded for IPv6 if they expect to communicate effectively with  
IPv6-only peers.  IPv6-only applications can get along just fine  
using IPv4-compatible IPv6 addresses (or some other address type  
representing the IPv4->IPv6 function) when keeping track of the  
translate IPv6 addresses of their IPv4-only peers.


--
james woodyatt <jhw@apple.com>
member of technical staff, communications engineering