[address-policy-wg] IPv4 reserved space

Hi,

> As we see ISPs and community would like to have more IPv4 space in use.
> 
> I would like to ask a question what do people think about other side of
> IPv4 numeration space. Because we have in IPv4 a lot of addresses not in
> use at all but that space could be easy used.
> 
> 240.0.0.0/4	Reserved (former Class E network)	RFC 1700

I remember people looking into that years ago, and the conclusion was that in too many routers and operating systems the 240/4 block was hard-coded as unusable. I just checked the Linux source code and that restriction was removed there around 2008, but similar code was present in so many different places that it wasn't a viable solution.

Remember that it wouldn't just be the organisation getting a block from 240/4, it would also affect everybody trying to communicate with them. Operating systems refusing to connect to a 240/4 address would make any website hosted on a 240/4 address badly reachable. Same for DNS servers hosted on such an address etc.

> it's 16 */8 networks. More then 256 Millions of routable and never used
> IPv4.


That is actually not that much. In 2012 when we ran out of free IPv4 space for normal use the rate of allocation world-wide was more than a /8 per month. Even if we could use 240/4 these days, it would probably last us a year or so, and then we would be back where we are today.

So in short:
- 240/4 use is problematic
- software needs to be changed in many places to make it usable
- same for configurations (bogon filters etc)
- it wouldn't last us much longer than a year anyway
- we still need to move to IPv6 because we will have again run out

Even shorter: we would use up 240/4 in less time than we would need to make it actually usable, so let's not.

If we are changing stuff let's just spend our energy on implementing IPv6 instead.

Cheers,
Sander

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