A straightforward transition plan (was: Re: V6 still not supported)

JORDI PALET MARTINEZ jordi.palet at consulintel.es
Mon Mar 28 13:44:04 UTC 2022

I don't think we can say that NAT64 is a disaster. I will say so if we want to keep IPv4 only hosts in the "6" side, of course it doesn't work. However, that's why we moved further with 464XLAT. And the demonstration is that most of the operators are using it.

I think in your picture you're missing 2 phases:
4) IPv6-only with IPv4aaS (we have 5 technologies, see RFC8585 for a summary of what is needed in the CPEs), when there is still a significant amount of IPv4 traffic in the customer LANs.
5) IPv6-only with IPv4aaS when IPv4 traffic is residual in most of the customers LANs. How fast we move to this phase depends on more and more devices, and apps using IPv6.

The advantage is:
a) The job is done in the CPE (no need for a more powerful one, etc.), customers are not aware of it. Part of the job is done in the operators networks, of course, but it is comparable and much cheaper, in terms of OpEx and CapEx, to alternatives such as dual-stack or NAT444/CGN.
b) When moving to 5 above, the operators can measure the reduction on the usage of the NAT64 (in the case of 464XLAT), and even in the usage of IPv4 public addresses, so they can transfer them, so laggers can use them for their own transition. On the side of the customers, there is nothing to do. You may remove IPv4, but actually is not costing you "anything" to keep it.


El 28/3/22, 15:23, "NANOG en nombre de Philip Homburg" <nanog-bounces+jordi.palet=consulintel.es at nanog.org en nombre de pch-nanog-2 at u-1.phicoh.com> escribió:

    >If by ?straightforward transition plan? one means a clear and rational set of 
    >options that allows networks to plan their own migration from IPv4-only to IPv
    >6, while maintaining connectivity to IPv4-only hosts and with a level of effor
    >t reasonable comparable to just running IPv4, then I would disagree, as such a
    >n "IPng transition plan? was achievable, expected, and we collectively failed 
    >to deliver on it (as noted below) 

    I'm a bit confused about the achievable part.

    Obviously, the adoption of IPv6 without a clear transition plan was a process
    failure. However, it is not clear to me that waiting a few years would 
    have brought something much better. And waiting more than a decade would
    mean that today there would not be a mature IPv6.

    Transition to IPv6 so far seems to have consisted of 3 phases:
    1) Lots of tunnels due lack of a wide spread IPv6 backbone.
    2) Early adopters being happy that they can run IPv6 native, usually as
       dual stack.
    3) Lots of people looking into IPv6-only.

    I'd say 1) mostly worked. 6to4 was a bit of mess. But otherwise tunnels
    worked. Obviously, deploying IPv6 using tunnels is a lot more complex
    than deploying native IPv4 without NAT. 
    From a technical perspective 2) just works. From an operational perspective
    it is about twice as expensive as IPv4-only. So 2) is popular with people
    who really want IPv6. 

    The big issue is 3). If we look at the current internet, there are parties
    who lack IPv4 addresses and want to switch to IPv6. Obviously, they
    want to be IPv6-only. The lack of IPv4 address makes dual stack even harder.
    On the other hand, there are parties who have enough IPv4 addresses and
    have no reason to switch to IPv6.

    So we are clearly in the situation of 'migration from IPv4-only to IPv6,
    while maintaining connectivity to IPv4-only hosts'

    It should be clear that an IPv4-only host only speaks IPv4. This means that
    communication with an IPv4-only host has to be IPv4. So either the
    IPv6-only host or something in the network has to speak IPv4. If the
    IPv6 host speaks IPv4 then we get dual stack, which has been rejected
    as a broken solution. Technically, it is also possible to tunnel IPv4
    packets, then the host is in some sense dual stack, but most of the network
    is not. However, automatic tunnel configuration is hard, and tunnels
    tend to be fragile.

    So the only option is a device in the network that translates between
    IPv6 and IPv4. Currently we have such a protocol, NAT64. And from
    a technical point of view it is a disaster.

    Looking back, we can say that the only feature of IPv6 that makes people
    invest in IPv6 is the bigger address space. So it is safe to say that
    most of the internet would have waited to invest in IPv6 until we were
    (almost) out of IPv4 addresses. So by its very nature this transation 
    between IPv6 and IPv4 would have NAT component.

    In my opinion, It is clear that during the time IPv6 was developed, any
    solution involving NAT would have been rejected.

    So I'm confused, what transition technology was achievable (also in the
    political sense) but not delivered?

    If there is a magical transition technology that allows an IPv6-only host to
    talk to an IPv4-only host, then let's deploy it.

IPv4 is over
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