Earlier quoted context omitted.
Which is why Room 641A is filled with Juniper gear. https://en.wikipedia.org/wiki/Room_641A
That doesn't make any sense, the operators of Room 641A don't need to backdoor their own gear.
The Wikipedia article says, as do other accounts, that beam splitters were used to tap into fiber optic lines. That might in fact be how it was done, but I do not think that was necessary.
IIRC, Juniper core routers were (uniquely, at the time?) capable of duplicating traffic on a NIC to another NIC without performance impact on capacity as a whole. This would have made them particularly suitable for mass surveillance that would not show up in network management metrics.