Setting sensible max-prefix limits

Wed Aug 18 13:38:30 UTC 2021

On Wed, 18 Aug 2021 11:33:09 +0200
Lars Prehn <lprehn at mpi-inf.mpg.de> wrote:

> As I understand by now, it is highly recommended to set a max-prefix 
> limit for peering sessions. Yet, I can hardly find any recommendations 
> on how to arrive at a sensible limit.

Maybe because there isn't a simple, universal approach to setting it.
Probably like a lot of people, historically I'd set it to
some % over the current stable count and then manually adjust when the
limits were about to be breached, or often was the case when they were
and I wasn't ready for it. Not ideal.

I've never felt the automation of this setting however was worth the
effort.  Of course I am not usually responsible for hundreds of routers
and thousands of peering sessions.

At the risk of advocating for more junk in BGP or the RPKI, a max prefix
setting might be something that could be set by the announcing peer in
a BGP message, or possibly as an RPKI object with an associated ASN.
I'll let the masses debate how that would work and all the reasons that
isn't ideal, but I'm not sure there is a one-size-fit all solution for
this in the near term.

John