Re: any dangers of filtering every /24 on full internet table to preserve FIB space ?

[Mike Hammett <nanog () ics-il net>]

Feasibility of adding some middleware that culls unneeded routes (existing more specific and aggregate routes pointing 
to the same next hop), when that table starts to fill? 


Not great for passing downstream, but should fill a need internally. 




----- 
Mike Hammett 
Intelligent Computing Solutions 
http://www.ics-il.com 

Midwest-IX 
http://www.midwest-ix.com 

----- Original Message -----

From: "Edvinas Kairys" <edvinas.email () gmail com> 
To: "NANOG Operators' Group" <nanog () nanog org> 
Sent: Monday, October 10, 2022 9:58:45 AM 
Subject: any dangers of filtering every /24 on full internet table to preserve FIB space ? 


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