Partial vs Full tables

William Herrin bill at
Fri Jun 5 14:54:51 UTC 2020

On Thu, Jun 4, 2020 at 8:02 PM James Breeden <James at> wrote:

> I come to NANOG to get feedback from others who may be doing this. We have
> 3 upstream transit providers and PNI and public peers in 2 locations. It'd
> obviously be easy to transition to doing partial routes for just the peers,
> etc, but I'm not sure where to draw the line on the transit providers. I've
> thought of straight preferencing one over another. I've thought of using
> BGP filtering and community magic to basically allow Transit AS + 1
> additional AS (Transit direct customer) as specific routes, with
> summarization to default for the rest. I'm sure there are other thoughts
> that I haven't had about this as well....

Hi James,

When I was at the DNC in 2007, we considered APNIC-region /8s lower
priority than ARNI region (for obvious reasons) so I got some extra life
out of our router by pinning most APNIC /8s to a few stable announcements,
preferring one transit to the other with a fallback static route. This
worked in the short term but I wouldn't want to do it as a long term

As a more generic approach: filter distant (long AS path) routes because
there's a higher probability that they're reachable from any transit with
about the same efficiency.

Any time you summarize routes, you WILL lose connectivity during network
partitions. Which defeats part of the purpose of having BGP with multiple
transits. Partitions are rare but they can persist for days (*cough* cogent
*cough*). So that's a risk you should plan for.

Bill Herrin

William Herrin
bill at
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