5 ms·

Not by default it’s not. An ipv6-only deployment cannot natively access an ipv4 network, there is no backwards comparability in the protocol.

ahoef 2y ago
One of the many missed opportunities of IPv6.
- ziedaniel1 2y ago
  What are some others?
- teraflop 2y ago
  I keep seeing people say this, but nobody ever takes the next step of proposing how this "missed opportunity" might have been fixed. The reality is that there is no possible way IPv6 could have been designed that would both solve the IPv4 address exhaustion problem and natively interoperate with IPv4. When you send a packet to an IPv4 host, it needs to know where to send the response, and there simply aren't enough bits in the IPv4 header to fit more than 2^32 possible addresses. You need something in the middle to translate between IPv6 and IPv4 addresses, and we already have that: it's called NAT64. It works the same way you would expect NAT to, and just like NAT on IPv4, there's no need to codify it as an explicit part of the IP protocol itself.
  - Bluecobra 2y ago
    I think it was bad timing. We might have been able to migrate to IPv6 wholesale when the Internet was much smaller in the early 90s. One thing that comes to mind is the kumbaya moment when everyone got together to switch from BGP v3 to BGP v4 to support CIDR.
    - dboreham 2y ago
      That was the plan. V6 was killed by NAT and the commercial forces that promoted its use.
      - kstrauser 2y ago
        "Killed" is a bit harsh, given that it's half of all Google's traffic. A huge chunk of that is probably from cell phones where IPv6 support is the norm.
    - Borg3 2y ago
      Not really.. IPv6 was theoretically ready in 1997. But, it was theoretical. It was still buggy. In 2000s Internet expansion skyrocketed and noone really cared about IPv6. Buggy, too different from IPv4, basically overengineered. They made prediction that was absolutly off.. And thats why adoption is crappy.
      - andrewshadura 2y ago
        IPv6 is not overengineered. It is, in fact, simpler in design than IPv4.
    - throw0101a 2y ago
      > We might have been able to migrate to IPv6 wholesale when the Internet was much smaller in the early 90s. In the early 1990s IPng/IPv6 was not yet invented, and when it was being considered they realized a flag-day (like (mostly) happened with NCP->IP) was unlikely: We believe that it is not possible to have a "flag-day" form of transition in which all hosts and routers must change over at once. The size, complexity, and distributed administration of the Internet make such a cutover impossible. Rather, IPng will need to co-exist with IPv4 for some period of time. There are a number of ways to achieve this co-existence such as requiring hosts to support two stacks, converting between protocols, or using backward compatible extensions to IPv4. Each scheme has its strengths and weaknesses, which have to be weighed. Furthermore, we note that, in all probability, there will be IPv4 hosts on the Internet effectively forever. IPng must provide mechanisms to allow these hosts to communicate, even after IPng has become the dominant network layer protocol in the Internet. * https://datatracker.ietf.org/doc/html/rfc1726#section-5.5 https://datatracker.ietf.org/doc/html/rfc1726#section-5.5
commandersaki 2y ago
I'm pretty sure we're discussing about connecting to the Internet. What I understood is being implied is that ipv6 has little utility if it cannot access ipv4, but is not the case the other way around.
- Arnt 2y ago
  How would v6 connect to v4? Specifically, how would the return packets back from v4 to v6 be routed?
  - yjftsjthsd-h 2y ago
    Through a NAT64 NAT. Which is extra work, but not that bad.
    - Arnt 2y ago
      Well, we have that. What GP refers to is a missed opportunity, so NAT64 can't be what GP has in mind.
  - deleted 2y ago
    [deleted]
  - commandersaki 2y ago
    Not really my point, was just pointing out there's scant incentive to transition from the incumbent.
    - Arnt 2y ago
      And to do that, you mentioned a condition that's either ① satisfied by current IPv6 or ② impossible to satisfy, and for which that's clear on even a moment's reflection. Not sure which of those two you had in mind, but in either case: Please don't do such things.
      - commandersaki 2y ago
pclmulqdq 2y ago
I get that you're trying to make a point, but NAT64 makes this not a real problem. Every practical use of IPv6 can access IPv4 hosts.

ahoef 2y ago

One of the many missed opportunities of IPv6.

ziedaniel1 2y ago
What are some others?
teraflop 2y ago
I keep seeing people say this, but nobody ever takes the next step of proposing how this "missed opportunity" might have been fixed. The reality is that there is no possible way IPv6 could have been designed that would both solve the IPv4 address exhaustion problem and natively interoperate with IPv4. When you send a packet to an IPv4 host, it needs to know where to send the response, and there simply aren't enough bits in the IPv4 header to fit more than 2^32 possible addresses. You need something in the middle to translate between IPv6 and IPv4 addresses, and we already have that: it's called NAT64. It works the same way you would expect NAT to, and just like NAT on IPv4, there's no need to codify it as an explicit part of the IP protocol itself.
- Bluecobra 2y ago
  I think it was bad timing. We might have been able to migrate to IPv6 wholesale when the Internet was much smaller in the early 90s. One thing that comes to mind is the kumbaya moment when everyone got together to switch from BGP v3 to BGP v4 to support CIDR.
  - dboreham 2y ago
    That was the plan. V6 was killed by NAT and the commercial forces that promoted its use.
    - kstrauser 2y ago
      "Killed" is a bit harsh, given that it's half of all Google's traffic. A huge chunk of that is probably from cell phones where IPv6 support is the norm.
  - Borg3 2y ago
    Not really.. IPv6 was theoretically ready in 1997. But, it was theoretical. It was still buggy. In 2000s Internet expansion skyrocketed and noone really cared about IPv6. Buggy, too different from IPv4, basically overengineered. They made prediction that was absolutly off.. And thats why adoption is crappy.
    - andrewshadura 2y ago
      IPv6 is not overengineered. It is, in fact, simpler in design than IPv4.
  - throw0101a 2y ago
    > We might have been able to migrate to IPv6 wholesale when the Internet was much smaller in the early 90s. In the early 1990s IPng/IPv6 was not yet invented, and when it was being considered they realized a flag-day (like (mostly) happened with NCP->IP) was unlikely: We believe that it is not possible to have a "flag-day" form of transition in which all hosts and routers must change over at once. The size, complexity, and distributed administration of the Internet make such a cutover impossible. Rather, IPng will need to co-exist with IPv4 for some period of time. There are a number of ways to achieve this co-existence such as requiring hosts to support two stacks, converting between protocols, or using backward compatible extensions to IPv4. Each scheme has its strengths and weaknesses, which have to be weighed. Furthermore, we note that, in all probability, there will be IPv4 hosts on the Internet effectively forever. IPng must provide mechanisms to allow these hosts to communicate, even after IPng has become the dominant network layer protocol in the Internet. * https://datatracker.ietf.org/doc/html/rfc1726#section-5.5 https://datatracker.ietf.org/doc/html/rfc1726#section-5.5

commandersaki 2y ago

I'm pretty sure we're discussing about connecting to the Internet. What I understood is being implied is that ipv6 has little utility if it cannot access ipv4, but is not the case the other way around.

Arnt 2y ago
How would v6 connect to v4? Specifically, how would the return packets back from v4 to v6 be routed?
- yjftsjthsd-h 2y ago
  Through a NAT64 NAT. Which is extra work, but not that bad.
  - Arnt 2y ago
    Well, we have that. What GP refers to is a missed opportunity, so NAT64 can't be what GP has in mind.
- deleted 2y ago
  [deleted]
- commandersaki 2y ago
  Not really my point, was just pointing out there's scant incentive to transition from the incumbent.
  - Arnt 2y ago
    And to do that, you mentioned a condition that's either ① satisfied by current IPv6 or ② impossible to satisfy, and for which that's clear on even a moment's reflection. Not sure which of those two you had in mind, but in either case: Please don't do such things.
    - commandersaki 2y ago

pclmulqdq 2y ago

I get that you're trying to make a point, but NAT64 makes this not a real problem. Every practical use of IPv6 can access IPv4 hosts.