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0 pointsthrow0101c1mo ago0 comments

> So 10.20.30.40 would be an IPv4 address, and 10.20.30.40:fa:be:4c:9d could be an IPv6 address. With the :00:00:00:00 suffix being equivalent to the IPv4 version.

> 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...

Or:

> For any 32-bit global IPv4 address that is assigned to a host, a 48-bit 6to4 IPv6 prefix can be constructed for use by that host (and if applicable the network behind it) by appending the IPv4 address to 2002::/16.

> For example, the global IPv4 address 192.0.2.4 has the corresponding 6to4 prefix 2002:c000:0204::/48. This gives a prefix length of 48 bits, which leaves room for a 16-bit subnet field and 64 bit host addresses within the subnets.

* https://en.wikipedia.org/wiki/6to4

So you have to ship new code to every 'network element' to support your "IPv4+" plan. Just like with IPv6.

So you have to update DNS to create new resource record types ("A" is hard-coded to 32-bits) to support the new longer addresses, and have all user-land code start asking for, using, and understanding the new record replies. Just like with IPv6. (A lot of legacy code did not have room in data structures for multiple reply types: sure you'd get the "A" but unless you updated the code to get the "A+" address (for "IPv4+" addresses) you could never get to the longer with address… just like IPv6 needed code updates to recognize AAAA, otherwise you were A-only.)

You need to update socket APIs to hold new data structures for longer addresses so your app can tell the kernel to send packets to the new addresses. Just like with IPv6. In any 'address extension' plan the legacy code cannot use the new address space; you have to:

* update the IP stack (like with IPv6)

* tell applications about new DNS records (like IPv6)

* set up translation layers for legacy-only code to reach extended-only destination (like IPv6 with DNS64/NAT64, CLAT, etc)

You're updating the exact same code paths in both the "IPv4+" and IPv6 scenarios: dual-stack, DNS, socket address structures, dealing with legacy-only code that is never touched to deal with the larger address space.

Deploying the new "IPv4+" code will take time, there will partial deployment of IPv4+ is no different than having partial deployment of IPv6: you have islands of it and have to fall back to the 'legacy' IPv4-plain protocol when the new protocol fails to connect:

* https://en.wikipedia.org/wiki/Happy_Eyeballs

"Just adding more bits" means updating a whole bunch of code (routers, firewalls, DNS, APIs, userland, etc) to handle the new data structures. There is no "just": it's the same work for IPv6 as with any other idea.

(This idea of "just add more addresses" comes up in every discussion of IPv6, and people do not bother thinking about what needs to change to "just" do it.)

> If IPv4 were more painfully broken then the switch would have happened long ago.

IPv4 is very painful for people not in the US or Western Europe that (a) were now there early enough to get in on the IPv4 address land rush, or (b) don't have enough money to buy as many IPv4 addresses as they need (assuming someone wants to sell them).

So a lot of areas of the world have switched, it's just that you're perhaps in a privileged demographic and are blind to it.

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zamadatix1mo ago

> IPv4 is very painful for people not in the US or Western Europe that (a) were now there early enough to get in on the IPv4 address land rush, or (b) don't have enough money to buy as many IPv4 addresses as they need (assuming someone wants to sell them).

The lack of pain is not really about the US & Western Europe have plenty of addresses or something of that nature, it's that alternative answers such as NAT and CG-NAT (i.e. double NAT where the carrier uses non-public ranges for the consumer connections) deployments are still growing faster in those regions than IPv6 adoption when excluding cellular networks (they've been pretty good about adopting IPv6 and are where most of the IPv6 traffic in those regions comes from).

jcgl1mo ago

I think your summary is really great. One of the better refutations I've seen about the "what about v4 but longer??" question.

However, I think people do get tripped up by the paradigm shift from DHCP -> SLAAC. That's not something that is an inevitable consequence of increasing address size. And compared to other details (e.g. the switch to multicasting, NDP, etc.), it's a change that's very visible to all operators and really changes how things work at a conceptual level.

zamadatix1mo ago

The real friction with SLAAC was that certain people (particularly some at Google) tried to force it as the only option on users, not that IPv6 ever forced it as the only option. The same kind of thing would likely occur with any new IP version rolling out.

For comparison IPv4 had:

  - Static (1980 - original spec)
  - RARP   (1984 - standalone spec)
  - BOOTP  (1985 - standalone spec)
  - DHCP   (1993 - standalone spec)

And for IPv6:

  - Static (1995 - pre, 1998 final spec)
  - SLAAC  (1996 - pre standalone, 1998 final standalone)
  - DHCPv6 (2003 - standalone)

Some of these have had subsequent minor updates, e.g. DHCP was updated in 1997 and so on.

WorldMaker1mo ago

SLAAC isn't something that is an inevitable consequence of increasing address size, it's something that is a useful advantage of increasing address size. Almost no one had big enough blocks in IPv4 where "just choose a random address and as long as no else seems to be currently claiming it it is yours" was a viable strategy for assigning an address.

There are some nice benefits of SLAAC over DHCP such as modest privacy: if device addresses are randomized they become harder to guess/scan; if there's not a central server with a registration list of every device even more so (the first S, Stateless). That's a great potential win for general consumers and a far better privacy strategy than NAT44 accidental (and somewhat broken) privacy screening. It's at odds with corporate device management strategies where top-down assignment "needs to be the rule" and device privacy is potentially a risk, but that doesn't make SLAAC a bad idea as it just increases the obvious realization that consumer needs and big corporate needs are both very different styles of sub-networks of the internet and they are conflicting a bit. (Also those conflicting interests are why consumer equipment is leading the vanguard to IPv6 and corporate equipment is languishing behind in command-and-control IPv4 enclaves.)

wmf1mo ago

DHCPv6 now exists and every OS except Android supports it.

jcgl1mo ago

> except Android

That alone is significant.

Furthermore, DHCPv6 holds you back from various desirable things like privacy addresses and (arguably even more importantly) IPv6 Mostly.

throw0101d1mo ago

> Furthermore, DHCPv6 holds you back from various desirable things like privacy addresses and (arguably even more importantly) IPv6 Mostly.

Why would DHCPv6 hold back privacy addresses? Can't DHCPv6 servers generate random host address bits and assign them in DHCP Offer packets? Couldn't clients generate random addresses and put them in Request packets?

See perhaps OPTION_IA_TA (Temporary Address):

* https://datatracker.ietf.org/doc/html/rfc8415#section-21.5

* https://en.wikipedia.org/wiki/DHCPv6#Option_Codes

    DHCPv6 temporary addresses have the same properties as SLAAC
    temporary addresses (see Section 4.6).  On the other hand, the
    properties of DHCPv6 non-temporary addresses typically depend on the
    specific DHCPv6 server software being employed.  Recent releases of
    most popular DHCPv6 server software typically lease random addresses
    with a similar lease time as that of IPv4.  Thus, these addresses can
    be considered to be "stable, semantically opaque".  [DHCPv6-IID]
    specifies an algorithm that can be employed by DHCPv6 servers to
    generate "stable, semantically opaque" addresses.

* https://datatracker.ietf.org/doc/html/rfc7721#section-4.7

How does DHCPv6 hold back IPv6-mostly? First, most clients will send out a DHCPv4 request in case IPv4 is the only option, in which case IPv6-mostly can be signalled:

* https://datatracker.ietf.org/doc/html/rfc8925

And hosts would also have to send out an IPv6 RS, and the RA can signal IPv6-mostly:

* https://datatracker.ietf.org/doc/html/rfc8781

* https://datatracker.ietf.org/doc/html/draft-ietf-v6ops-6mops...

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zamadatix1mo ago

jcgl1mo ago

I think your summary is really great. One of the better refutations I've seen about the "what about v4 but longer??" question.

zamadatix1mo ago

For comparison IPv4 had:

  - Static (1980 - original spec)
  - RARP   (1984 - standalone spec)
  - BOOTP  (1985 - standalone spec)
  - DHCP   (1993 - standalone spec)

And for IPv6:

  - Static (1995 - pre, 1998 final spec)
  - SLAAC  (1996 - pre standalone, 1998 final standalone)
  - DHCPv6 (2003 - standalone)

Some of these have had subsequent minor updates, e.g. DHCP was updated in 1997 and so on.

WorldMaker1mo ago

wmf1mo ago

DHCPv6 now exists and every OS except Android supports it.

jcgl1mo ago

> except Android

That alone is significant.

Furthermore, DHCPv6 holds you back from various desirable things like privacy addresses and (arguably even more importantly) IPv6 Mostly.

throw0101d1mo ago

> Furthermore, DHCPv6 holds you back from various desirable things like privacy addresses and (arguably even more importantly) IPv6 Mostly.

See perhaps OPTION_IA_TA (Temporary Address):

* https://datatracker.ietf.org/doc/html/rfc8415#section-21.5

* https://en.wikipedia.org/wiki/DHCPv6#Option_Codes

    DHCPv6 temporary addresses have the same properties as SLAAC
    temporary addresses (see Section 4.6).  On the other hand, the
    properties of DHCPv6 non-temporary addresses typically depend on the
    specific DHCPv6 server software being employed.  Recent releases of
    most popular DHCPv6 server software typically lease random addresses
    with a similar lease time as that of IPv4.  Thus, these addresses can
    be considered to be "stable, semantically opaque".  [DHCPv6-IID]
    specifies an algorithm that can be employed by DHCPv6 servers to
    generate "stable, semantically opaque" addresses.

* https://datatracker.ietf.org/doc/html/rfc7721#section-4.7

How does DHCPv6 hold back IPv6-mostly? First, most clients will send out a DHCPv4 request in case IPv4 is the only option, in which case IPv6-mostly can be signalled:

* https://datatracker.ietf.org/doc/html/rfc8925

And hosts would also have to send out an IPv6 RS, and the RA can signal IPv6-mostly:

* https://datatracker.ietf.org/doc/html/rfc8781

* https://datatracker.ietf.org/doc/html/draft-ietf-v6ops-6mops...

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