A Question

I had this question recently posed to me in an interview:

You are a cloud services provider.

You have multiple remote customers separated by any number of AS's from you.

You advertise your BGP prefixes along an optimal path and a sub-optimal path where, receiving both, all customer routers will by default choose the optimal path.

For specific reasons you want to force customer A to install prefixes learned through the sub-optimal path, without affecting any other customers.

You have control over your network only, and no control over any customer or transit networks.

How would you do this?




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Admittedly I had to be led to the answer and then it was obvious. I was disappointed to learn after the fact that this is a corner case, dug up to see how you thought through this. With some big name companies, I expect the toughest questions, further expecting that this reflects on the complexity of the work itself. Too many engineers who interview end up researching the tough questions from Google. It's a fair question in its own right, but it distracted from the general plainness of the actual work to be done.

Still, a few good questions that serve as food for though after are well worth the rigor of the interview.