For the APRANET in 1969, the BBN Interface Message Processor (IMP) did the packet routing.
(It’s another cool artifact of history in the back room, awaiting installation in the new Computer History Museum exhibition hall.)
The Honeywell 516 minicomputer inside had only 6,000 words of software (in 12K of core memory) and monitored network status and statistics. Cost: $82,200
The first transmission between UCLA and SRI took place on October 29, 1969.
Larry Roberts, architect of the Internet, diagrammed some of that rich history at our CEO Summit.