Class D addresses? was: Redploying most of 127/8 as unicast public

William Herrin bill at herrin.us
Sat Nov 20 19:51:24 UTC 2021


On Sat, Nov 20, 2021 at 11:02 AM Michael Thomas <mike at mtcc.com> wrote:
> Even if it has some niche uses, I seriously doubt
> that it needs 400M addresses. If you wanted to reclaim ipv4 addresses it
> seems that class D and class E would be a much better target than loopback.

Hi Mike,

If you follow the links there are multiple proposals split by the
address space they apply to. There's one for 240/4 and another for
224/4 in addition to the one we've been discussing for 127/8.

Obviously the one for 240/4 is the lowest hanging fruit of the bunch.

> There is just as big a block of addresses with class D addresses for
> broadcast. Is broadcast really even a thing these days?

Multicast is not the same as broadcast and yes, it's a thing. Mainly
it's a thing confined to the local broadcast domain but in that scope
it's quite widely used. A lot of routing protocols (including OSPF)
use multicast, for example. However, while it's widely used there
aren't very many -different- things using it so only a tiny fraction
of the 224/4 space has been assigned to anything in common use.

If I had to guess, changing 224/4 is probably the biggest lift. The
other proposals mainly involve altering configuration, removing some
possibly hardcoded filters and in a few cases waiting for silicon to
age out of the system. Changing 224/4 means following a different code
path which does something fundamentally different with the packets --
unicast instead of multicast.

Regards,
Bill Herrin



-- 
William Herrin
bill at herrin.us
https://bill.herrin.us/


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