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I'm trying to find a way of "identifying" anycast IPs. This turns out to be rather tricky, as it's (usually) dependant on BGP routes directing you to the nearest available host.

What are common techniques of identifying if a certain IP address is a unicast or anycast IP?

I've thought of tracerouting the IP several times and find any differences in the last hops (usually the datacenter where it resides), but with dynamic paths (sometimes you hop via switch-1, sometimes via switch-2) this turned out to be quite unreliable.

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I'm wondering what is the problem that you're trying to solve? Or are you just curious? –  dsolimano Mar 5 '11 at 18:54
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up vote 2 down vote accepted

Routes change all the time, for all kinds of reasons. Also, in a stable environment there is no real reason for an anycasted ip block to change routes. So that's not good to go on.

The best way would be to find some open looking glasses, have them show the route tables to that specific network. An anycasted network would have serveral routes, often differing depending on where you queried.

To confirm, you can use the traceroute facilities offered by those looking glasses. Compare the latency/path from different countries/cities. If the network beats the speed of light (quick responses no matter what the continent), it's a sure bet it is anycasted.

To practice this, check out hosts in the DNS services offered by the large providers. They are easy to find in the nameservers of large corporations.

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