nanog mailing list archives
Re: maximum ipv4 bgp prefix length of /24 ?
From: Owen DeLong via NANOG <nanog () nanog org>
Date: Mon, 2 Oct 2023 09:45:29 -0700
On Oct 2, 2023, at 01:18, Nick Hilliard <nick () foobar org> wrote: William Herrin wrote on 02/10/2023 08:56:All it means is that you have to keep an eye on your FIB size as well, since it's no longer the same as your RIB size.the point Jacob is making is is that when using FIB compression, the FIB size depends on both RIB size and RIB complexity. I.e. what was previously a deterministic 1:1 ratio between RIB and FIB - which is straightforward to handle from an operational point of view - becomes non-deterministic. The difficulty with this is that if you end up with a FIB overflow, your router will no longer route.
It was never 1:1 if you have more than one path for any route. The FIB only contains the chosen path(s) to any destination even without fib compression.
That said, there are cases where FIB compression makes a lot of sense, e.g. leaf sites, etc. Conversely, it's not a generally appropriate technology for a dense dfz core device. It's a tool in the toolbox, one of many.
Even at a dense DFZ core device, there are a large number of single-origin consecutive /24s in the table which can be fib compressed with no loss. For a long time, someone was teaching up and coming operators in Asia that they should always announce everything as disaggregated /24s to guard against route hijacking. This unfortunate practice persists still, making FIB compression quite practical even at core nodes. Owen
Nick
Current thread:
- Re: maximum ipv4 bgp prefix length of /24 ?, (continued)
- Re: maximum ipv4 bgp prefix length of /24 ? Owen DeLong via NANOG (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? William Herrin (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Tom Beecher (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Matthew Petach (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Tim Franklin (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Mark Tinka (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Delong.com via NANOG (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Matthew Petach (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? William Herrin (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Chris Hills (Oct 03)
- Re: maximum ipv4 bgp prefix length of /24 ? Owen DeLong via NANOG (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Jakob Heitz (jheitz) via NANOG (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Jon Lewis (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Owen DeLong via NANOG (Oct 02)
- Re: maximum ipv4 bgp prefix length of /24 ? Elmar K. Bins (Oct 04)
- Re: maximum ipv4 bgp prefix length of /24 ? Mark Tinka (Oct 04)
- Re: maximum ipv4 bgp prefix length of /24 ? Elmar K. Bins (Oct 04)
- Re: maximum ipv4 bgp prefix length of /24 ? Owen DeLong via NANOG (Oct 04)
- Re: maximum ipv4 bgp prefix length of /24 ? Musa Stephen Honlue (Oct 04)