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by anderstrier 1629 days ago
> In other words: The current IPv6 specifications don't allow public IPv6 addresses to send packets to public IPv4 addresses. They also don't allow public IPv4 addresses to send packets to public IPv6 addresses. Public IPv6 addresses can only exchange packets with each other. The specifications could have defined a functionally equivalent public IPv6 address for each public IPv4 address, embedding the IPv4 address space into the IPv6 address space; but they didn't.

Why didn't they? What are the arguments against this solution?

You would have to upgrade the software and OS of systems using IPv4-only to understand the IPv6 IP header. (Which is much simpler than upgrading to support IPv6 AND assigning IPv6 addresses)

I guess the bigger problem is that all routers in the path between an IPv6-only host and an IPv4-only host would have to support IPv6 to parse the destination IPv4/IPv6 address and make the proper routing decision.

This would make "IPv6 to IPv4 and vice-versa" traffic only work for some, depending on which ISPs has upgraded their equipment to support IPv6, and which IPv4-only hosts has upgraded their software+OS to support IPv6. This could result in IPv6 getting a very bad reputation, further delaying adoption.

Anything I am missing?
1 comments
throw0101a 1629 days ago
>> In other words: The current IPv6 specifications don't allow public IPv6 addresses to send packets to public IPv4 addresses.

> Why didn't they? What are the arguments against this solution?

They did. See "Stateless IP/ICMP Translation Algorithm (SIIT)"

   This document specifies a transition mechanism algorithm in addition
   to the mechanisms already specified in [TRANS-MECH].  The algorithm
   translates between IPv4 and IPv6 packet headers (including ICMP
   headers) in separate translator "boxes" in the network without
   requiring any per-connection state in those "boxes".  This new
   algorithm can be used as part of a solution that allows IPv6 hosts,
   which do not have a permanently assigned IPv4 addresses, to
   communicate with IPv4-only hosts.  The document neither specifies
   address assignment nor routing to and from the IPv6 hosts when they
   communicate with the IPv4-only hosts.
* https://datatracker.ietf.org/doc/html/rfc2765 (2000)

* https://datatracker.ietf.org/doc/html/rfc7915 (update in 2016)

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