202401100645.AYC Re: IPv4 address block

Thu Jan 11 09:40:14 UTC 2024

On Wed, Jan 10, 2024 at 11:06 AM Tom Beecher <beecher at beecher.cc> wrote:
>>
>> There's a whole bunch of software out there that makes certain
>> assumptions about allowable ranges. That is, they've been compiled with
>> a header that defines ..
>
>
> Of course correct. It really depends on the vendor / software / versions in an environment. A lot of vendors removed that years ago, because frankly a lot of large networks have been using 240/4 as pseudo RFC1918 for years. Others have worked with smaller vendors and open source projects to do the same.
>
> It's consistently a topic in the debates about 240/4 reclassification.

There's debates still? I gave up. After making 240/4 and 0/8 work
across all of linux and BSD and all the daemons besides bird (which
refused the patch , I took so much flack that I decided I would just
work on other things. So much of that flack was BS - like if you kill
the checks in the OS the world will end - that didn't happen. Linux
has had these two address ranges just work for over 5 years now.

240/4 is intensely routable and actually used in routers along hops
inside multiple networks today, but less so as a destination.

I would really like, one day, to see it move from reserved to unicast
status, officially. I would have loved it if 0/8 was used by a space
RIR, behind CGNAT, for starters, but with a plan towards making it
routable. I am not holding my breath.

The principal accomplishment of the whole unicast extensions project
was to save a nanosecond across all the servers in the world on every
packet by killing the useless 0/8 check. That patch paid for itself
the first weekend after that linux kernel deployed. It is the
simplest, most elegant, and most controversial patch I have ever
written.

https://news.ycombinator.com/item?id=20430096

>
> On Wed, Jan 10, 2024 at 10:45 AM Michael Butler <imb at protected-networks.net> wrote:
>>
>> On 1/10/24 10:12, Tom Beecher wrote:
>> > Karim-
>> >
>> > Please be cautious about this advice, and understand the full context.
>> >
>> > 240/4 is still classified as RESERVED space. While you would certainly
>> > be able to use it on internal networks if your equipment supports it,
>> > you cannot use it as publicly routable space. There have been many
>> > proposals over the years to reclassify 240/4, but that has not happened,
>> > and is unlikely to at any point in the foreseeable future.
>>
>> While you may be able to get packets from point A to B in a private
>> setting, using them might also be .. a challenge.
>>
>> There's a whole bunch of software out there that makes certain
>> assumptions about allowable ranges. That is, they've been compiled with
>> a header that defines ..
>>
>> #define IN_BADCLASS(i)  (((in_addr_t)(i) & 0xf0000000) == 0xf0000000)
>>
>>         Michael
>>

-- 
40 years of net history, a couple songs:
https://www.youtube.com/watch?v=D9RGX6QFm5E
Dave Täht CSO, LibreQos