Re: [arch-d] Treating "private" address ranges specially

[Brian E Carpenter <[e-mail]>]

Hi,

On 31-Mar-21 22:07, Ted Hardie wrote:

<snip>

> The document's description of the address space architecture is:
> 
> 
>       2.1. IP Address Space
> 
> Every IP address belongs to an IP address space, which can be one of three different values:
> 
>  1. local: contains the local host only. In other words, addresses whose target differs for every device.
> 
>  2. private: contains addresses that have meaning only within the current network. In other words, addresses whose target differs based on network position.
> 
>  3. public: contains all other addresses. In other words, addresses whose target is the same for all devices globally on the IP network.

The problem is that this classification is worse than heresy; it's nonsense.

1) local. That seems trivially true (assuming that it covers virtual hosts, not just physical ones). Or is it? If a device has multiple interfaces (physical or virtual) which might lie in different administrative domains, each of which has several IP addresses, including but not limited to loopback addresses, are they all equally "local"?

2) private. There is no definition of "private" address in any IETF document. There is no way of looking at the bits in an address and determining that it's private, because there's no definition of private.

3) public. Ditto. Globally reachable != public. "Globally reachable" itself is an over-simplification. See recent very loud discussions in IPv6-land about ULA addresses.

The attempt to use the IANA registry to determine things that are undefined is just nonsense. It's an attempt to over-simplify something that is inherently complex. The ground truth about address scope exists only in the entire Internet's routing tables, and simply *cannot* be deduced from the bits in an address.

BTW, whoever designed the Python ipaddress module got this wrong too.

So IMHO this whole effort is fundamentally misguided and should be scrapped.

   Brian