On 2022-10-10 09:39, Jay Hennigan wrote:
On 10/10/22 07:58, Edvinas Kairys wrote:
We're considering to buy some Cisco boxes - NCS-55A1-24H. That box
has 24x100G, but only 2.2mln route (FIB) memory entries. In a near
future it will be not enough - so we're thinking to deny all /24s to
save the memory. What do you think about that approach - I know it
could provide some misbehavior. But theoretically every filtered /24
could be routed via smaller prefix /23 /22 /21 or etc. But of course
it could be a situation when denied /24 will not be covered by any
smaller prefix.
If so, a better approach might be to apply a max AS rule and take full
tables plus a default from both (all). Something like "bgp maxas-limit
4" will optimize routing down to /24 but drop routes with long AS
paths and punt to default, reducing your table size at the cost of
sub-optimal routing to destinations that are going to take a
convoluted path anyway.
And run something like netflow to determine high traffic AS paths, and
optimize those into your filtering.
