I like that idea.
----- Mike Hammett Intelligent Computing Solutions http://www.ics-il.com Midwest-IX http://www.midwest-ix.com ----- Original Message ----- From: "Jay Hennigan" <j...@west.net> To: nanog@nanog.org Sent: Monday, October 10, 2022 10:39:06 AM Subject: Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? On 10/10/22 07:58, 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 ? Are you multi-homed? If not you can simply take a default. If so, a better approach might be to apply a max AS rule and take full tables plus a default from both (all). Something like "bgp maxas-limit 4" will optimize routing down to /24 but drop routes with long AS paths and punt to default, reducing your table size at the cost of sub-optimal routing to destinations that are going to take a convoluted path anyway. -- Jay Hennigan - j...@west.net Network Engineering - CCIE #7880 503 897-8550 - WB6RDV