[db48x]

> Well, an ostensible advantage of IPv6 is publicly routable addresses. I know how to configure my internal IPv4 network with host table entries and so on. If I move to IPv6 then my "internal" network address space is at the whim of my ISP.

This is not quite correct. You have two simple options for avoiding this: DNS and SLAAC. By giving all of your hosts dns names you don’t have to care about the individual addresses much. If they change just update the dns zone.

The second is to configure a Unique Local Address for each host using SLAAC. Have your router announce a prefix inside of fd00::/7 so that every one of your computers ends up with a private address as well as the public one. This is like using a reserved private address in IPv4, such as 10.0.0.0/8, except that there are a lot more possible networks. There is only one 10.0.0.0/8, but the convention with IPv6 ULAs is to generate 40 random bits and use them to make a /40. Add 16 more bits for a subnet id to create a /64 that your router will advertise as a prefix. This is probably overkill for most of us, but it does enable us to merge networks without causing address collisions. You can keep using them no matter what happens. Even changing ISP won't change these addresses.

Of course the third option is to buy IP transit service instead of internet access service. You can then go to your local RIR and ask them to assign you your own address block. Announcing that address block using BGP gives you a permanent block of routable addresses that follows you from ISP to ISP. But most people find that to be a bit of a hassle compared to consumer–grade internet service.

[everdrive]

>Of course the third option is to buy IP transit service instead of internet access service. You can then go to your local RIR and ask them to assign you your own address block.

Or I could just log into my router and disable IPv6

[db48x]

That’s boring.

[ninkendo]

> By giving all of your hosts dns names you don’t have to care about the individual addresses much. If they change just update the dns zone

"just" update the zone? Yikes. I prefer to not take that downtime in the first place. (And I know from experience, I've written hooks for dhcpcd that automatically reconfigure my zone file, firewall rules, rad.conf, etc, if I get a new network prefix! But I don't pretend that this is a workable approach for everyone.)

> The second is to configure a Unique Local Address for each host using SLAAC

Yes, this is the way. Where you used to use RFC1918 addresses, just use ULA. It's simple and fits the mental model you used to have with IPv4. You don't even need NAT, just give both the GUA and ULA addresses to each host, and use the ULA everywhere you want LAN-like semantics.

[strenholme]

“There is only one 10.0.0.0/8”

Also:

- There are 16 172.{16-31}.0.0/16s (I used 172.23 because Docker uses one of these)

- There are 256 192.168.{0-255}.0/8s

And that’s just what RFC1918 gives us. There are other private subnets defined in newer RFCs.

I like IPv6 but it caused issues with browsers accepting my Letsencrypt certs on my website, so my website is now IPv4 only.

“Announcing that address block using BGP gives you a permanent block of routable addresses that follows you from ISP to ISP.”

Enough people have done this that BGP networking has become a real mess at the ISP level. Can BGP really handle every person in the world doing this?

[gerdesj]

Class B or the 12 block is 172.16.0.0/12. So: 10/8, 172.16/12, 192.168/16.

[db48x]

Yes, I know that there are other private subnets in IPv4. My comparison was specifically between IPv6 ULAs and 10.0.0.0/8 specifically because of the size. You won’t have to renumber your networks when you grow in size because 2⁷² addresses is enough for just about any organization.

> Can BGP really handle every person in the world doing this?

Eh, probably not. I did say that it wasn’t for everyone. You have to fill out a form, and then they announce to the world that you did it. And if you configure your BGP announcements wrong you’ll get laughed at by everyone who watches those things. Most people can’t handle it.

On the other hand, the VP of Network Operations at the ISP I used once promised that they’ll honor BGP announcements even from residential customers. I guess once it’s automated that it doesn’t cost them anything extra. Could be a fun hobby.

And if enough people do it then we can simply improve BGP. Anything we invent we can improve, right?

[cromka]

Very interesting, had no idea IPv6 had this as an option. Thanks for the write-up!

[db48x]

You’re welcome. Have fun with it!