People hate kludges and backward compatibility, but IPv4.1 with 5-byte addresses would have been the dominant standard by now.
This is thinking which appeals to people who don't understand the problem because it feels like a compromise, but you can't negotiate with silicon. If it expects a 4 byte address payload, then that's all it will ever handle.
Adding more bytes is exactly the same amount of redesign and replacement work as adding more. If the problem was solely software related, it would've been done by now.
Add a one-byte option into the header, give it an unassigned value (e.g. 6) and assume that any box that does not understand it will pass it through unchanged. Use it as the most significant byte of the address, and obsolete all routing equipment that doesn't understand it from the backbone so that they can be used to handle routing in one of the new 32-bit super-A class networks.
Sure it's ugly as hell, but it is just backward compatible enough to work.
Routers don't run packet addresses through software, they run then through silicon ASICs which know the address is 32 bits, that's it.
Your solution is literally how Cisco implemented IPv6 on a bunch of it's switches: the IPv6 routing path goes through the firmware and is slow as hell compared to the pure ASIC IPv4 handling. It didn't catch on because it was terrible at any scale (we were building Hadoop clusters, 100+ big data nodes with constrained throughout is money down the drain).
Your claim was that any change to the ASIC was the same design cost. But really? A 40-bit routing table design, where there is a 32-bit fall-back to preserve the top 8-bits vs a 128-bit routing table design. Why would these be the same cost?
When would you have done it? When the hardware was 5 years old? 10 years old? I've been on change operations where the hardware was over a decade old and our biggest concern was making sure we had replacement PSUs on hand since the thermal shock of a reboot might take them out.
This is the problem, you have absolutely no idea what anything costs or how it works - you're simply thinking "lifting those bits sounds heavy, what if we made them lighter?" as though a committee of engineers, designers and industry didn't spend a lot of time considering exactly that problem.
If you could add 1 byte in software and be done with it, it would have already happened.
You are arguing that all change has the same cost. I don't see your reasoning for this. A smaller change to a system has a lower cost in R&D, and a lower cost in manufacture.
Although it is probably true that the cost of updating all equipment dominates the cost of redesign, this is only an issue for a big bang update rather than a rolling upgrade.
As many have found out, unfortunately "any box that does not understand it will pass it through unchanged" is frequently false. What often happens is that a box which does not understand it silently drops the whole packet, under the mistaken impression that it's an attempt to invade the network.
> Use it as the most significant byte of the address, and obsolete all routing equipment that doesn't understand it from the backbone
You'd have to not only obsolete all routing equipment, but also all end hosts. Consider what happens when host A, which does not understand the option, receives a packet from host B, which has an address which requires the option; the reply packets from host A will never reach host B, since host A doesn't know it has to add the option.
These "just add another byte" solutions are often proposed in these discussions, and look deceptively simple at a first glance, but fall apart once you start looking at it in detail.
If you can articulate how this magic wand would work in practice we're all ears since you solved a worldwide problem, but I'm betting my salary that you can't.