BSD is very nearly where TCP/IP networking was invented. Yes, there were a several other IP stacks back in the 80's... But BSD was where it was at!
However... ISP core networking was usually the domain of high end Cisco kit, and that derived from the Stanford "Blue Box" multi-protocol router written by Bill Yeager, and basically stolen from Stanford by Lerner & Bosack to start Cisco. They were forced to resign from Stanford, and the resulting scandal was settled in 1987 with a licensing agreement.
http://pdp10.nocrew.org/docs/cisco.html