<i>>The 512,000 route limitation can be increased to a higher number, for details see this Cisco doc</i><p>and that doc goes ahead to explain how to increase the limit at the cost of space for IPv6. Worse: The sample code (which everybody is going to paste) doubles the space for IPv4 at the cost of nearly all the IPv6 space, even though we should soon cross the threshold when we're going to see more IPv6 growth than IPv4 growth.
That's a nice site with some interesting graphs. They are a bit higher level than the simplest level of surveillance systems so I wouldn't start at an inappropriately higher level to see if there even is a problem. One lower level simple technique to determine or isolate if a problem even exists is to monitor TCP port 179 traffic rate (aka BGP) between your BGP speakers and your peers / customers. If the routers have nothing to talk about between each other, then there IS nothing to talk about, at least WRT routing problems. Or if one of "my" routers was having an intense discussion with another router, I knew something was up in that general direction. And it can be basically completely passive and completely isolated from the routing systems, which is cool. Just sniff -n- graph TCP 179 bandwidth over time. You'd like to see a nice horizontal low line of keepalives. Reboots or restarts make a nasty spike, never got much agreement but log-y-axis is probably for the best.<p>Obviously this only finds routing level problems. We can send a /17 to you just fine, but if you're having an IGP problem and sending every byte of it to null, well, from the BGP perspective that's just fine. Much as if you insist on sending us RFC1918 traffic we'll drop that route and traffic for you just fine, just like we had to eat your 0/0 route you're trying to get us to advertise to the entire internet. I think my head still has a flat spot from hitting it on the desk arguing with people.<p>Its been a decade since I did that stuff professionally at a regional ISP and I really don't miss it. Not much, anyway.
I like Renesys's take [1] on the subject as well:<p><i>Note that there’s no good exact opinion about the One True Size of the Internet — every provider we talk to has a slightly different guess. The peak of the distribution today (the consensus) is actually only about 502,000 routes, but recognizably valid answers can range from 497,000 to 511,000, and a few have straggled across the 512,000 line already.</i><p>[1] <a href="http://www.renesys.com/2014/08/internet-512k-global-routes/" rel="nofollow">http://www.renesys.com/2014/08/internet-512k-global-routes/</a><p>It's interesting how they explain that since there's no true consensus for the actual size of the routing table, the "event" of crossing the 512k barrier has frankly already begun ... and, so far, hasn't been catastrophic, nor likely to be.