"Tactical" /24 announcements

Mon Aug 9 17:29:40 UTC 2021

----- On Aug 9, 2021, at 9:22 AM, Masataka Ohta mohta at necom830.hpcl.titech.ac.jp wrote:

Hi,

> It should be 14M.

Just for fun, I did the math. A total of 16,777,216 /24s fit in 32 bits. Take away all the reserved space as per IANA (this is 1,266,696 /24s, see below), and we end up with 16,777,216 - 1,266,696 = 15,510,520 potential /24 advertisements.

The largest FIB table I have seen (hi Jim!) was 3,563,546 routes in hardware. This was in a lab environment, of course.

Thanks,

Sabri

https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml 
Subnet		Number of /24s

0.0.0.0/8	65536
10.0.0.0/8	65536
100.64.0.0/10	16384
127.0.0.0/8	65536
169.254.0.0/16	256
172.16.0.0/12	4096
192.0.0.0/24	1
192.0.2.0/24	1
192.31.196.0/24	1
192.52.193.0/24	1
192.88.99.0/24	1
192.168.0.0/16	256
192.175.48.0/24	1
198.18.0.0/15	512
198.51.100.0/24	1
203.0.113.0/24	1
240.0.0.0/4	1048576

Total reserved	1,266,696