maximum ipv4 bgp prefix length of /24 ?

Mon Oct 9 18:35:38 UTC 2023

> On Oct 5, 2023, at 15:51, Geoff Huston <gih at apnic.net> wrote:
> 
>> On 6 Oct 2023, at 6:13 am, Owen DeLong <owen at delong.com> wrote:
>> 
>> Ratio of FIB to RIB is only part of the equation.
>> 
>> IPv6 is NOT under the disaggregation pressure that IPv4 is under because there is no pressure (other than perhaps scarcity mentality from those that don’t properly understand IPv6) to dense-pack IPv6 assignments or undersize IPv6 allocations.
>> 
>> Look at the difference in prefixes per ASN across the two tables and that tells a much grimmer story for IPv4 in terms of RIB growth vs. IPv6.
> 
> 
> hmm - IPv4 is at [1], IPv6 is at [2]
> 
> Now I’m trying to understand what your grimmer story for IPv4 might be here Owen. Since 2005 the number of IPv4 FIB entries per origin AS has increased fropm 8 to 12 in the past 20 years - or a 50% increase. Over ther same period the number of IPv6  prefix advertisements per origin AS has increased from 1.5 to 6, or a fourfold increase. If anything, the IPv6 story appears to me to be a far greater cause for concern, but you may have a different interpretation of this data.

I admit I’m surprised that IPv6 has gotten to an average of 6, but it would be interesting to know why that is. Honestly, I expected it would end up closer to 4. I wonder how much of that is PI stub networks being originated by upstream transit networks. I also wonder to what extent the “average” might be misleading here. Is it a few ASs with large numbers of prefixes and mostly 1-2 prefixes per AS or is the average representative?

I know that in IPv4, for example, there are several ASs originating MANY prefixes and lots of smaller ASs originating <4 prefixes.

My grimmer picture for IPv4 is about the intrinsic pressure to deaggregate that comes from the ever finer splitting of blocks in the transfer market and the ever finer grained dense packing of hosts into prefixes that is forced from address scarcity. Those pressures don’t (or at least shouldn’t) exist for IPv6.

YMMV

Owen