Comment by icehawk
It would fit in RAM but then you actually have to search through RAM. I have a router that is doing a very modest 3gbps of traffic, or about 2000pps that all need lookups, and about 40 updates per second that goes into that table.
I should also mention that's 40 updates per second for a default free zone of about 950,000 routes. 8 billion routes would be an minimum update frequency of ~370,000 routes per second assuming the same stability.