maximum ipv4 bgp prefix length of /24 ?

Fri Sep 29 05:21:35 UTC 2023

On Thu, Sep 28, 2023 at 9:54 PM Owen DeLong <owen at delong.com> wrote:
> > In principle, a company could make a business out of announcing a
> > large block from a bunch of peering points and then tunneling (vpn)
> > parts of it back to customers with sub-/24 assignments. With a broad
> > enough selection of peering points, the routing would not be too
> > inefficient. And it would divorce the IP addresses from the last-mile
> > Internet infrastructure, allowing you to take your addresses with you
> > as long as you kept paying the tunnel company.
>
> Actually, such a service would be much easier to stand up as a bunch
> of virtual routers running on VPS instances in various cloud providers.
> Simple as standing up a VPS running Debian 12 and FRR, then sell
> routed blocks to people.

Sure, depending on the data rates. I do something similar with my own network.

It would be a challenge to push multiple gbps of data this way. Just
because a user's demand for IP addresses is small doesn't mean their
demand for bandwidth is.

> > You're thinking of DRAM. But that's not the way it works. Some routers
> > use heavily parallel routing engines, each of which need enough dram
> > to hold the full forwarding information base and which can suffer from
> > CPU cache exhaustion even then. Others use an expensive kind of memory
> > called a TCAM that's very fast but both expensive and power hungry, so
> > generally not sized for huge numbers of tiny routes.
>
> Trio and Later generations of Juniper MX line cards (which are getting fairly
> long in the tooth these days) can handle more than 5M routes in the FIB.

Maybe. That's where my comment about CPU cache starvation comes into
play. I haven't delved into the Juniper line cards recently so I could
easily be wrong, but if the number of routes being actively used
pushes past the CPU data cache, the cache miss rate will go way up and
it'll start thrashing main memory. The net result is that the
achievable PPS drops by at least an order of magnitude.

No free lunch I'm afraid. The exact characteristics differ, but both
approaches grow rapidly in expense with the size of the forwarding
information base (FIB).

Regards,
Bill Herrin

-- 
William Herrin
bill at herrin.us
https://bill.herrin.us/