> I don't know much about your imaging servers: Do they accept incoming https connections, or is it some other kind of TCP or UDP protocol?

Yes

>why do you need to stick with IPv4?

To support devices and routes that do not have ipv6 support?

>1: If you require IPv4, that needs to be part of the contract with your ISP. If they just arbitrarily turned you off, it means that you didn't contract for the services you thought you had.

That is correct in principle. Although, in the absence of a contract, if a service has been provided for a long time in one way, I'd say there's an argument for breach of contract when that way changes for the worst.

Another argument for breach of contract, which can work jointly with the previous, are industry standards, as far as they define the terms that are implied by common words like "internet connection".

Finally, there's the specifications themselves, since the service is billed as "internet", one can refer to the Internet Protocol Specification, although if they do offer IPv6, that might be reasonably considered a substitute, it is a material change that was not agreed to originally (this being a pre IPv6 contract). That said, an IPv4 with a local address might technically still be defined as internet, what is broken in this case is TCP, not the IP, although by lacking a public IP address, TCP is broken via an IP protocol failure, so there's an argument that something is being sold as Internet but it isn't really internet, there's no written contract necessary, the term used to describe the product creates the contract in the same way that selling a carton labeled Milk would create a contract based on milk coming from mammaries of a domestic mammal, and not pressed Soy Juice with artificial coloring.

>2: IPv6 is supposed to solve a lot of these problems... So again, why can't you move to IPv6?

I'm open to proposals to moving IPv6, I'm not content with having that be forced and removing it from people and institutions, if there's a shortage, then that means no new IP addresses can be issued, why are we normalizing the removal of IPv4 addresses? Are they being removed from lower priority users in order to serve high priority usecases? If so is a hospital a low priority user?

The main issue with IPv6 seems to be IPv6 proponents that try to kill IPv4, no one will migrate if you force them to, if you propose, we will consider.

Have you noted that in the mainline Linux build config file, the option to enable IPv4 functionality is CONFIG_LEGACY_IP= ?

I can tell you that in cicd for production Linux systems today, we have

  CONFIG_LEGACY_IP=""

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What might work well for your organization is ZeroTier which will make you immune to what any ISPs do. The downside is your organization would be dependent on ZeroTier, but ZeroTier is much less likely to screw you over than any ISP.

  https://www.zerotier.com/

I appreciate your speculation on the principles of contract law. Like you, I believe those principles should be upheld and I believe in morality. If you lived under a monarchy and I were of the monarch, I would cross-examine your ISP in public and solve your problem in minutes. I would also on occasion take someone to the side of the road and chop off their head in front of the entire village, and everyone would know on a visceral level they are all much better off with someone taking out the trash now and then.

But, as many technical workers know, the contract stuff takes months or years to resolve, and technical issues involving IP addresses are best worked around with technical approaches.

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What I would suggest your network team (you and whoever) do in your shoes is:

- set up NAT64 and DNS64 at the edges of subnets that contain devices that don't do IPv6 properly, because if these devices do not have updates to do IPv6 properly then they are broken in a fundamental way, and a workaround is necessary;

- dictate that starting on December 1st, all new devices and VMs have IPv6 addresses with all userspace services listening on IPv6 addresses or some nftables rule to kludge IPv6:$port -> 127.0.0.1:$port if necessary, with firewall configured to block that IPv6 traffic, then at a later date firewalls not blocking those IPv6 addresses, then at a later date prohibit any new IPv4 addresses being assigned anywhere with special exception to devices tagged "legacy" or "end of life" requiring documentation of such;

- use a combination of IPv6 GUA addresses assigned by whatever ISP and IPv6 ULA addresses chosen by your team -- in IPv6, multiple local gateways and multiple addresses on a network interface issued by those local gateways via RA is relatively a norm rather than an exception (requires userspace tooling in IPv4, DHCP doesn't have this functionality), so leverage this advantage;

- use IPv6 AH (authenticated headers) wherever possible;

- because in an ideal world, ISPs would behave consistently and IPv6 GUA addresses would always be stable, but we aren't living in an ideal world, so be ready to update your internal DNS to drop AAAA records containing IPv6 GUA that an upstream ISP fumbled;

- or, if you have the internal resources, register your own AS and command your own official block of IPv6 addresses;

- use a combination of OpenTOFU (Terraform) and Salt or Ansible, all versioned with Git, be very strict with your team about versioning with Git, to manage everything, and use

  terraform plan -detailed-exitcode

- move userspace services to Podman where possible.

Personally I like Salt. I know Ansible is more popular out there with more inertia.

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>> why are we normalizing the removal of IPv4 addresses?

This was normalized a long time ago actually. "The future is already here, it's just not evenly distributed".

You and I are total strangers on different corners of the globe. You may not like what you're about to read, but it's better that you get a hint where the wind is blowing sooner than not.

If my team were consulting with your organization's execs and we caught a hint that the existing internal resources were not already proactively staying current with internet protocol (which is IPv6), we would point out there is urgency to start right away with emphasis that the existing internal team is over two decades behind staying current.

Or, if a detected hint the internal team were at all resistant to IPv6, we would advise the executive team to start developing a plan to flush out the replacements for the internal team ASAP.

Many network engineers at many ISPs would gladly drop all IPv4 traffic if they thought they could get away with it.

IPv6 only seems more complicated if you still need to unlearn IPv4. IPv6 does have a steeper learning curve, but once that learning curve is overcome, IPv6 is actually much simpler than IPv4. More people than not don't like reading RFCs, but professionals do slowly read RFCs on their own time.