Similar discussion from a couple of months ago: https://news.ycombinator.com/item?id=46468625

I personally feel that IPv6 is one of the clearest cases of second system syndrome. What we needed was more address bits. What we got was a nearly total redesign-by-committee with many elegant features but had difficult backwards compatibility.

https://en.wikipedia.org/wiki/Second-system_effect

▲

adrian_b 2 hours ago | parent | next [-]

In my opinion the redesign of IPv6 was perfectly fine. The IPv6 headers are significantly simpler that those of IPv4 and much easier to process at great speed.

There was only 1 mistake, but it was huge and all backwards compatibility problems come from it. The IPv4 32-bit address space should have been included in the IPv6 address space, instead of having 2 separate address spaces.

IPv6 added very few features, but it mostly removed or simplified the IPv4 features that were useless.

▲

fanf2 16 minutes ago | parent | next [-]

There are several ways to map the IPv4 address space into the IPv6 address space, going right back to the first IPv6 addressing architecture RFC. Every compatibility protocol added a new one.

IPv6 added IPSEC which was backported to IPv4.

IPv6 tried to add easy renumbering, which did’t work and had to be discarded.

IPv6 added scoped addresses which are halfbaked and limited. Site-scoped addresses never worked and were discarded; link-scoped addresses are mostly used for autoconfiguration.

IPv6 added new autoconfiguration protocols instead of reusing bootp/DHCP.

▲

throw0101d 43 minutes ago | parent | prev | next [-]

> The IPv4 32-bit address space should have been included in the IPv6 address space, instead of having 2 separate address spaces.

> Addresses in this group consist of an 80-bit prefix of zeros, the next 16 bits are ones, and the remaining, least-significant 32 bits contain the IPv4 address. For example, ::ffff:192.0.2.128 represents the IPv4 address 192.0.2.128. A previous format, called "IPv4-compatible IPv6 address", was ::192.0.2.128; however, this method is deprecated.[5]

* https://en.wikipedia.org/wiki/IPv6#IPv4-mapped_IPv6_addresse...

▲

xorcist 2 hours ago | parent | prev [-]

> The IPv4 32-bit address space should have been included in the IPv6 address space,

That's ... exactly how IPv6 works?

Look at the default prefix table at https://en.wikipedia.org/wiki/IPv6_address#Default_address_s... .

Or did you mean something else? You still need a dual stack configuration though, there's nothing getting around that when you change the address space. Hence "happy eyeballs" and all that.

	▲	iso1631 2 hours ago \| parent [-]
		> You still need a dual stack configuration though, there's nothing getting around that when you change the address space Yes there is, at least outside of the machine. All you need to do is have an internal network (100.64/16, 169.254/16, wherever) local to the machine. If you machine is on say 2001::1, then when an application attempts to listen on an ipv4 address it opens a socket listening on 2001::1 instead, and when an application writes a packet to 1.0.0.1, your OS translates it to ::ffff:100:1. This can be even more hidden than things like internal docker networks. Your network then has a route to ::ffff:0:0/96 via a gateway (typically just the default router), with a source of 2001::1 When the packet arrives at a router with v6 and v4 on (assume your v4 address is 2.2.2.2), that does a 6:4 translation, just like a router does v4:v4 nat The packet then runs over the v4 network until it reaches 1.0.0.1 with a source of 2.2.2.2, and a response is sent back to 2.2.2.2 where it is de-natted to a destination of 2001:1 and source of ::ffff:100.1 That way you don't need to change any application unless you want to reach ipv6 only devices, you don't need to run separate ipv4 and ipv6 stacks on your routers, and you can migrate easilly, with no more overhead than a typical 44 nat for rfc1918 devices. Likewise you can serve on your ipv6 only devices by listening on 2001::1 port 80, and having a nat which port forwards traffic coming to 2.2.2.2:80 to 2001::1 port 80 with a source of ::ffff:(whatever) (using colons as a deliminator wasn't great either, you end up with http://[2001::1]:80/ which is horrible)

▲

lxgr 2 hours ago | parent | prev [-]

Which IPv6 “gratuitious” features (i.e. anything other than the decision to make a breaking change to address formats and accordingly require adapters) would you argue made adoption more difficult?

IPv6 gets a lot of hate for all the bells and whistles, but on closer examination, the only one that really matters is always “it’s a second network and needs me to touch all my hosts and networking stack”.

Don’t like SLAAC? Don’t use it! Want to keep using DHCP instead? Use DHCPv6! Love manual address configuration? Go right ahead! It even makes the addresses much shorter. None of that stuff is essential to IPv6.

In fact, in my view TFA makes a very poor case for a counterfactual IPv4+ world. The only thing it really simplifies is address space assignment.

▲

avidiax an hour ago | parent | next [-]

It's not that they loaded it up with features, it's that elegance was prized over practicality.

Simplifying address space assignment is a huge deal. IPv4+ allows the leaves of the network to adopt IPv4+ when it makes sense for them. They don't lose any investment in IPv4 address space, they don't have to upgrade to all IPv6 supporting hardware, there's no parallel configuration. You just support IPv4 on the terminals that want or need it, and on the network hardware when you upgrade. It's basically better NAT that eventually disappears and just becomes "routing".

	▲	lxgr an hour ago \| parent [-]
		> They don't lose any investment in IPv4 address space What investment? IP addresses used to be free until we started running out, and I don't think anything of value would be lost for humanity as a whole if they became non-scarce again. > they don't have to upgrade to all IPv6 supporting hardware But they do, unless you're fine with maintaining an implicitly hierarchical network (or really two) forever. > It's basically better NAT How is it better? It also still requires NAT for every 4x host trying to reach a 4 only one, so it's exactly NAT. > that eventually disappears Driven by what mechanism?

▲

iso1631 an hour ago | parent | prev [-]

Having both a real address, a link-local address, and a unique local address, and the requirement to use the right one in each circumstance

The removal of arp and removal of broadcast, the enforcement of multicast

The almost-required removal of NAT and the quasi-relgious dislike from many network people. Instead of simply src-natting your traffic behind ISP1 or ISP2, you are supposed to have multiple public IPs and somehow make your end devices choose the best routing rather than your router.

All of these were choices made in addition to simply expanding the address scope.

	▲	lxgr an hour ago \| parent [-]
		> Having both a real address, a link-local address, and a unique local address, and the requirement to use the right one in each circumstance Only use the real one then (unless you happen to be implementing ND or something)! > The removal of arp and removal of broadcast, the enforcement of multicast ARP was effectively only replaced by ND, no? Maybe there are many disadvantages I'm not familiar with, but is there a fundamental problem with it? > The almost-required removal of NAT Don't like that part? Don't use it, and do use NAT66. It works great, I use it sometimes!