SDN Internet Router (sir)

Christopher Morrow morrowc.lists at
Thu Jan 5 18:27:08 UTC 2023

On Thu, Jan 5, 2023 at 11:18 AM Mike Hammett <nanog at> wrote:

> Initially, my thought was to use community filtering to push just IXes,
> customers, and defaults throughout the network, but that's obviously still
> sub-optimal.
> I'd be surprised if a last mile network had a ton of traffic going to any
> more than a few hundred prefixes.

I think in a low-fib box at the edge of your network your choices are:
  "the easy choice, get default, follow that"

  "send some limited set of prefixes to the device, and default, so you MAY
choose better for the initial hop away"

you certainly can do the second with communities, or route-filters
(prefix-list) on the senders, or....
you can choose what prefixes make the cut (get the community(ies)) based on
traffic volumes or expected destination locality:
   "do not go east to go west!"

these things will introduce toil and SOME suboptimal routing in some
instances... perhaps it's better than per flow choosing left/right though
and the support calls related to that choice.

In your NOLA / DFW / ATL example it's totally possible that the networks in
question do something like:
  "low fib box in tier-2 city (NOLA), dfz capable/core devices in tier-1
city (DFW/ATL), and send default from left/right to NOLA"

Could they send more prefixes than default? sure... do they want to deal
with the toil that induces? (probably not says your example).

SDN isn't really an answer to this, though.. I don't think. Unless you
envision that to lower the toil ?
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