Re: maximum ipv4 bgp prefix length of /24 ?

["Jakob Heitz \(jheitz\) via NANOG" <nanog () nanog org>]

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/