nanog mailing list archives
Re: any dangers of filtering every /24 on full internet table to preserve FIB space ?
From: Jay Hennigan <jay () west net>
Date: Mon, 10 Oct 2022 08:39:06 -0700
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 - jay () west net Network Engineering - CCIE #7880 503 897-8550 - WB6RDV
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 ? William Herrin (Oct 11)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Matthew Petach (Oct 16)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? William Herrin (Oct 16)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Owen DeLong via NANOG (Oct 16)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Andrey Kostin (Oct 12)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? William Herrin (Oct 12)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? David Conrad (Oct 12)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Andrey Kostin (Oct 14)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Jon Lewis (Oct 12)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Joe Provo (Oct 15)
- Re: any dangers of filtering every /24 on full internet table to preserve FIB space ? Raymond Burkholder (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 ? Jay R. Ashworth (Oct 10)