about 5-7 years ago had a hard limit at 256.000 routes - and that came
quite close for a number of ISPs. The hardware upgrade to support 1 million
routes did cost significant money (like, 10.000-50.000 EUR/router), and
it does not truly support "1 million IPv4" routes, if you also have IPv6
and MPLS in your network - more like 700.000 IPv4 routes in typical
deployments. Now, before the big discussion starts: there is other
gear in the market that scales up to 2 million, etc., but I wanted to
point out that these are real-world hard limits, and the amount of "headroom"
we have between "what is out there today" (500k) and "what some of the
fairly widely deployed core routers can do today" (700k) is not so big
that we want to risk an explosion by factor 2.