"Tactical" /24 announcements

William Herrin bill at herrin.us
Mon Aug 9 17:17:44 UTC 2021

On Mon, Aug 9, 2021 at 9:24 AM Masataka Ohta
<mohta at necom830.hpcl.titech.ac.jp> wrote:
> William Herrin wrote:
> > I did some math on this years ago and it worked out to about 8.5
> > million IPv4 routes.
> It should be 14M.

Doubtful. Like I said, I did the math. The question I asked at the time was:

IPv6 fails to overtake IPv4 and
IPv4 continues to be divided and redistributed to progressively
higher-value uses and
the /24 public Internet announcement boundary holds then

What will the terminal size of the IPv4 Internet BGP table be?

There are 2^24 = 16.8M /24s in the IPv4 address space.

Many of these are reserved for non-unicast uses, e.g. 224/3, 0/8
Many of the unicast addresses are reserved for non-public uses, e.g. 10/8, 127/8
Some portion of the assigned address space is used off-Internet in
valuable enough ways that its owners are unlikely to release it for
use on the Internet.
Some portion of the address space won't be disaggregated to /24
because their owners won't find it convenient
Some portion of the address space will have overlapping announcements
(/24s and the overlapping the /20, that sort of thing)

I no longer have the exact formula but I made some reasonable
assumptions for each of these factors and it worked out to 8.5 million
as the probable terminal size of the IPv4 table. There were error
bands too, I forget what they were, but nothing came even close to

Bill Herrin

William Herrin
bill at herrin.us

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