While I did allude to some of the complexity, my main point is that FIB compression does not allow you to install a FIB with less memory. Because you must be prepared for transients during which the FIB needs to store mostly uncompressed anyway. All it does is to increase convergence time. Kind Regards, Jakob From: William Herrin <bill@herrin.us> Date: Sunday, October 1, 2023 at 6:32 PM To: Jakob Heitz (jheitz) <jheitz@cisco.com> Cc: nanog@nanog.org <nanog@nanog.org> Subject: Re: maximum ipv4 bgp prefix length of /24 ? On Sun, Oct 1, 2023 at 5:40 PM Jakob Heitz (jheitz) via NANOG <nanog@nanog.org> wrote:
Among the issues: Suppose the FIB has all the /24 components to make a /20, so it programs a /20. Then one of the /24's changes nexthop. It now has to undo all that compression
Yeah... all this stuff is on the same level of complexity as implementing a B-Tree. Standard task on the road to an undergraduate computer science degree. Compared to decoding a BGP update message, where nearly everything is variable length and you have to nibble away at the current field to find the start of the next field, this is a cakewalk. It doesn't actually get complicated until you want to do more than just joining adjacent address blocks. Regards, Bill Herrin -- William Herrin bill@herrin.us https://bill.herrin.us/