If you filter out /23 or longer you cut the v4 table size about in half. I have done this with some edge and eyeball network clients that had really old or underpowered routing gear and upgrades were just not in the budget, and they could barely spell BGP.
I know of a number of ASNs with SUP720 era gear still in production this way in 2022 (the power bill is usually someone else’s budget!).
Be sure to take default from a couple upstreams and allow /24s for the peers on your IXP links that matter (CDN, etc) and your traffic is mostly fine. Maybe not always taking the most direct return path, but it gets there.
Inbound traffic distribution isn’t affected and that is all most eyeball networks care about.
On Mon, Oct 10, 2022 at 11:26 AM Nick Suan via NANOG <
nanog@nanog.org> wrote:
There's 69,055 pure /24's allocated or assigned directly from an RIRs. At least c,d,e, and g root servers only have /24s allocated to them. Major services like Cloudflare only advertise the /24 without advertising an aggregate.
Unless you're also getting a default from upstream, it sounds like you're going to end up wasting the money you saved on chasing down subtle brokenness.
On Mon, Oct 10, 2022, at 9:58 AM, Edvinas Kairys wrote:
Hello,
We're considering to buy some Cisco boxes - NCS-55A1-24H. That box has 24x100G, but only 2.2mln route (FIB) memory entries. In a near future it will be not enough - so we're thinking to deny all /24s to save the memory. What do you think about that approach - I know it could provide some misbehavior. But theoretically every filtered /24 could be routed via smaller prefix /23 /22 /21 or etc. But of course it could be a situation when denied /24 will not be covered by any smaller prefix.
What do you think about this approach ?
Also maybe you know - some advices for edge routers that have at least 8x100G interfaces and "good" memory for prefix count ? Thanks
Jim Troutman,
Pronouns: he/him/his
207-514-5676 (cell)