maximum ipv4 bgp prefix length of /24 ?

Thu Oct 5 19:11:11 UTC 2023

I think it needs to be slightly more nuanced than that…

Because IPv4 is driven to dense-packing and tight allocations, I think disaggregation of IPv4 will only increase over time.

The hope is that by issuing larger than needed blocks of IPv6, less disaggregation becomes necessary over time.

So far, that seems to be largely the case, with more than 50% of ASNs represented in the DFZ in IPv6, we see
roughly 191884 unique destinations in IPv6 and 942750 unique destinations in IPv4 (admittedly an instantaneous
snapshot a few moments ago from a single DFZ router, YMMV).

Even if we double the IPv6 prefix count or even quadruple it, we’re still looking at a much smaller level of disaggregation
in IPv6 than IPv4 in the current state.

Owen

> On Oct 4, 2023, at 22:49, Crist Clark <cjc+nanog at pumpky.net> wrote:
> 
> Been resisting adding to this thread...
> 
> But if the assumption is that networks will always eventually totally deaggregate to the maximum, we're screwed. Routing IPv4 /32s would be nothing. The current practice of accepting /48s could swell to about 2^(48 - 3) = 2^45 = 35184372088832.
> 
> What will prevent unrestricted growth of the IPv6 table if operators push everything out to /48 "to counter hijacks" or other misguided reasons?
> 
> On Wed, Oct 4, 2023 at 8:14 AM Owen DeLong via NANOG <nanog at nanog.org <mailto:nanog at nanog.org>> wrote:
>> If you maximally disaggregate to /24, you end up with about 12M fib entries. At /25 this doubles and you double it again for every bit you move right. 
>> 
>> At /24, we are on borrowed time without walking right. Also, the CPU in most routers won’t handle the churn of a 10M prefix RIB. 
>> 
>> Owen
>> 
>> 
>> > On Oct 4, 2023, at 03:15, Mark Tinka <mark at tinka.africa> wrote:
>> > 
>> > 
>> > 
>> >> On 10/4/23 12:11, Musa Stephen Honlue wrote:
>> >> 
>> >> Which one is easier,
>> >> 
>> >> 1. Convincing the tens of thousands of network operators and equipment vendors to modify configs and code to accept more specifics than /24, or
>> > 
>> > Equipment vendors can already support 10 million entries in FIB. They just ask for a little bit of cash for it.
>> > 
>> > Mark.
>> 
>> 

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