Shit got fucked up. I was out there for hours. The ISP guy was stumped. The customer was throwing up his hands, sure that yet again, it wasn't going to work. But by the second hour, the ISP's routing guy from their data center kept telling his own tech to put *me* on the phone, and asking me questions.
By the fourth hour, I made one final suggestion, ran traceroutes to all possible networks, and they all came up golden. Everything was working right. The customer's network was now running twice as fast as it was when I got there. The ISP's tech shook my hand and thanked me. The customer informed me there was a LOT more business to be done there.
And I played air guitar in my head the whole way out to the parking garage.