Some doubts on large scale BGP/AS design and black hole routing risk

Mark Tinka mark.tinka at
Sun Apr 3 22:17:28 UTC 2016

On 31/Mar/16 10:12, magicboiz at wrote:
> My questions are:
> 1. What could happen in the case of total failure in the redundant
> leased lines? Black hole routing between POPs?

If you have redundant backhaul that completely fails, you've got real

However, if that does happen, any traffic coming into each individual
PoP destined for users in the other PoP will fail. Only traffic
terminating for customers at that PoP will succeed.

> 2. What are the best design methods to avoid this scenario?

Work on your backhaul.

Originate specific routes that cover customers present in each PoP, with
the aggregate as a backup route.

You can run a tunnel across the Internet to simulate a backbone between
both PoP's, using your side of your upstream's IP addresses as the
tunnel end-point. Not elegant, but keeps you up.

>    2.1: adding a third POP creating a triangle? What if a POP looses
> connection with the other two POPs at the same time? Another black hole?

Your fixation on a complete backhaul outage is interesting.

Purchase backhaul from different service providers to increase your
chances of uptime.

>    2.2: requesting another prefix and allocating 1:1 prefix:POP, so in
> the scenario each POP only would announce its prefix to the upstreams?

See above re: originating more specific routes based on the customers
you have at each PoP.

>    2.3: other?

Work harder on your backhaul.

Yes, bad things can happen, and they do happen. But more than likely, if
a 3-PoP network loses all connectivity from each other, I think routing
will be a much smaller problem to solve in the grand scheme of things.


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