nanog mailing list archives
Re: any dangers of filtering every /24 on full internet table to preserve FIB space ?
From: William Herrin <bill () herrin us>
Date: Mon, 10 Oct 2022 08:26:22 -0700
On Mon, Oct 10, 2022 at 7:58 AM Edvinas Kairys <edvinas.email () gmail com> wrote:
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 ?
If you have a default route that works and you don't have any downstream customers which expect a full routing table, this is fine. You just won't get as good results with the /24s. Beware that MOST Internet /24 routes are NOT covered by a shorter prefix so unless you specifically cover them they will be lost. This will severely impact your Internet connectivity. The Internet FIB is around 900k IPv4 routes. You have years before exhausting a 2.2M table. Regards, Bill Herrin -- For hire. https://bill.herrin.us/resume/
Current thread:
- RE: any dangers of filtering every /24 on full internet table to preserve FIB space ?, (continued)
- RE: any dangers of filtering every /24 on full internet table to preserve FIB space ? Tobias Fiebig (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Geoff Huston (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? richey goldberg (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? David Bass (Oct 10)
- RE: any dangers of filtering every /24 on full internet table to preserve FIB space ? Tobias Fiebig (Oct 10)
- RE: any dangers of filtering every /24 on full internet table to preserve FIB space ? Adam Thompson (Oct 20)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Brandon Martin (Oct 21)
- RE: any dangers of filtering every /24 on full internet table to preserve FIB space ? Adam Thompson (Oct 24)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Jon Sands (Oct 27)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Jim Troutman (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Elmar K. Bins (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Mike Hammett (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? William Herrin (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Jeff Tantsura (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? William Herrin (Oct 10)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Matthew Petach (Oct 10)