Re: maximum ipv4 bgp prefix length of /24 ?

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

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
by reinstalling some of the routes and figuring out the minimum set of /21, /22, /23, /24
to make it happen. Then to avoid a transient, it needs to make before break.
Quite a bit of FIB programming needs to happen just to modify a single /24.
Then the next /24 in the set also modifies its nexthop. and so on for 100000 routes.
All because a peer link flapped.
Affecting convergence.
Then you need to buy a line card that can hold all the individual routes, because you
can't always compress, because not all the routes in your compressed set have the
same nexthop during a transient.
Finally, it's all nicely compressed.
Now what? You have lots of empty slots in your FIB.
I'm sure lots of nerds can come up with transient reduction algorithms, but I'd rather not.

Kind Regards,
Jakob

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Date: Sat, 30 Sep 2023 20:04:29 -0700
From: Owen DeLong <owen () delong com>

Not sure why you think FIB compression is a risk or will be a mess. It?s a pretty straightforward task.

Owen