Why IPv6 is so complicated • Hacker News Board

Re: Why IPv6 is so complicated

#301

Post by simoncion » Sat, May 02, 2026, 4:58 PM UTC

ninkendo wrote: post #275

api wrote: post #268

It’s not. It’s IPv4 with more bits and some changes to Ethernet level lookup. The SLAAC vs DHCPv6 mess is not really a problem with the core V6 spec.

The changes to Ethernet lookup mandate that you have a link-local address in addition to your “real” address, and this starts the ball rolling on the idea that machines have multiple IP addresses in general. Which makes privacy addresses commonplace, ULA+GUA addresses on the same machine, etc. I think this is the biggest change with IPv6: that a machine’s IP addresses is no longer its identity, and you can’t easily p…

> I think this is the biggest change with IPv6: that a machine’s IP addresses is no longer its identity, and you can’t easily predict what address will be used when connecting somewhere.

Can't you unset the "Use autonomous addressing" bit and set the "Use DHCPv6 for addressing and other config" bit in your RAs, and then refuse to hand out anything other than DHCPv6 Normal Addresses? Or do OS's ignore the fact that Temporary Addresses are an entire other category of DHCPv6 addresses and just go off and make their own "privacy addresses" off of the advertised prefix in the RA... ignoring the router's command to not use SLAAC for addressing? [0]

[0] Yes, I'm very aware that Android doesn't support anything that DHCPv6 provides other than getting an entire damn prefix delegated. For the duration of this discussion, let's ignore Android.

Re: Why IPv6 is so complicated

#302

Post by johncolanduoni » Sat, May 02, 2026, 5:00 PM UTC

tryauuum wrote: post #274

evilmonkey19 wrote: post #269

Personally, i feel it is complicated because ISPs are highly afraid of trying it. I understand that such novel technology would be risky to use. But after 20+ years there are still many countries, like Spain, which are barely using it. After that much time has passed, it is already well battle-tested. At this point, you don't want to make the move either because you are too afraid of anything or you have commercial r…

I think they are not afraid, they just see 0 reasons to without IPv6: everything works already, your customers can access any website with IPv6: ...what are the benifits to them? they still have to provide IPv4 to customers or do some ipv6 to ipv4 translation to make sure ipv4 websites still work (I've never worked at an ISP so my opinion might be useless)

There are some reasons, which is why you do see IPv6 use increasing. IPv4 exhaustion means that almost all mobile (and in some countries landline) internet connections have to access the IPv4 internet through Carrier Grade NAT. ISPs have to buy the equipment to operate these and pay for their maintenance, and they have to do so in proportion to how much traffic is stuck on the IPv4 internet. At a certain point making the necessary investments to send more traffic over IPv6 end-to-end becomes a better bet than continuing to maintain a growing CGNAT stack.

The tough part is that while ISPs can largely control whether their mobile and residential users have IPv6 available they can’t really do so for their business users, let alone arbitrary website operators they have no relationship with. So the reality is that everyone is going to have to maintain both 4to6 and 6to4 basically forever. But as it becomes less common it’ll no longer need to be especially fast or efficient and the costs to operate it will come down.

Re: Why IPv6 is so complicated

#303

Post by Ekaros » Sat, May 02, 2026, 5:01 PM UTC

dgoodell wrote: post #279

api wrote: post #268

It’s not. It’s IPv4 with more bits and some changes to Ethernet level lookup. The SLAAC vs DHCPv6 mess is not really a problem with the core V6 spec.

IPv4 + all the other stuff you need to actually make it work in the real world actually seems more complicated than IPv6 to me. Maybe they’re comparing the minimal implementation on a home network. But even then I’m not sure the claim holds up. People learned IPv4 when they were younger in a more incremental manner and take it for granted now.

ARP and DHCP really look really dirty whenever I look at them. Like pretty bad designs overall. From more neutral viewpoint it feels that whole stack would be better with something else than these clear hacks.

Re: Why IPv6 is so complicated

#304

Post by tonymet » Sat, May 02, 2026, 5:02 PM UTC

evilmonkey19 wrote: post #269

Personally, i feel it is complicated because ISPs are highly afraid of trying it. I understand that such novel technology would be risky to use. But after 20+ years there are still many countries, like Spain, which are barely using it. After that much time has passed, it is already well battle-tested. At this point, you don't want to make the move either because you are too afraid of anything or you have commercial r…

it’s the cost of dual stack. The transition from ipv4 to dual stack to ipv6-only goes from low cost, high cost, moderate cost.

There is little value to run dual stack.

Find me a business that would like to spend a lot of money on something of little value.

Re: Why IPv6 is so complicated

#305

Post by Dylan16807 » Sat, May 02, 2026, 5:03 PM UTC

amelius wrote: post #298

> Just adding bits to the address isn't as simple as it seems. They said the same in Y2K, and turned out that people were able to extend their date fields and the systems ran just fine.

You can add bits to your own systems fine.

When you want your packets to work on other people's routers, it stops being fine.

Re: Why IPv6 is so complicated

#306

Post by speedgoose » Sat, May 02, 2026, 5:03 PM UTC

I installed a new bare metal server from a european cloud provider this week.

Both my clean Debian and the rescue system couldn’t reach internet through IPv6 despite getting an address through DHCP.

I immediately permanently disabled IPV6. I usually do that pretty late in my installation scripts anyway.

I understand the perfect solution didn’t exist and still doesn’t exist, but it’s frustrating. I wish IPv6 could work reliably, not only on major CDNs, and that is appreciated. Then IPv4 would be a vanishing memory.

Re: Why IPv6 is so complicated

#307

Post by zhdc1 » Sat, May 02, 2026, 5:05 PM UTC

seanalltogether wrote: post #278

personally I just hate this -> http://[0123::4567]:5000/whatever

This. It’s ugly.

All of talk about the technical merits or demerits misses the point. I can spout of a dozen or more memorized IPv4 addresses. IPv6? Good luck.

Re: Why IPv6 is so complicated

#308

Post by Dylan16807 » Sat, May 02, 2026, 5:06 PM UTC

zadikian wrote: post #299

I disagree that it would've been just as hard anyway. The people who say "I just wanted v4 with more bits" have a point that most of these arguments completely ignore, but this one touches on it: Actually, we tried that: the "IPv4-Compatible IPv6 address" format was defined in [RFC3513] but deprecated by [RFC4291] because it turned out to be of no practical use for coexistence or transition. The practical use would'v…

Going all-in in what way?

The only thing I can think of is making it easier to run your local network v6-only. But if you're translating at the router like that, you don't need any particular mappings.

Re: Why IPv6 is so complicated

#309

Post by sethops1 » Sat, May 02, 2026, 5:08 PM UTC

Plasmoid wrote: post #290

hackthemack wrote: post #288

I think this is the kind of the topic that can be endlessly debated because you can not easily go back in time and test out alternate hypothesis. I will say that I do not like ipv6 because it tried to fix multiple accumulated problems. I know! How contrarian! How can you be against trying to fix things. But all of those issues made ipv6 a dual stack solution that replaced ipv4. Address exhaustion, Routing table scala…

> keeping backward operational compatibility It is not possible to be backwards compatibility with a larger address space

And yet 50% of the internet is using CGNAT just fine. The extra bits are just in a different place.

Re: Why IPv6 is so complicated

#310

Post by johncolanduoni » Sat, May 02, 2026, 5:08 PM UTC

zadikian wrote: post #299

I disagree that it would've been just as hard anyway. The people who say "I just wanted v4 with more bits" have a point that most of these arguments completely ignore, but this one touches on it: Actually, we tried that: the "IPv4-Compatible IPv6 address" format was defined in [RFC3513] but deprecated by [RFC4291] because it turned out to be of no practical use for coexistence or transition. The practical use would'v…

How would this have worked in practice, in a way that the NAT464/NAT64 schemes that most mobile operators use haven’t? Would IANA have dedicated some blocks of IPv4 to be used for IPv4-compatible IPv6 addresses on the public internet?