How to tell if something is anycasted?

Peter Boothe peter at
Wed May 17 06:59:54 UTC 2006

On Tue, 16 May 2006, David Hubbard wrote:

> So I'm looking at a company who offers anycasted DNS;
> how do I tell if it's really anycasted?  Just hop on
> different route servers to see if I can find different
> AS paths and then do traceroutes to see if they suggest
> the packets are not ending in the same location?
> >From my routers' perspective I don't see a difference,
> but then I don't think I should, correct?

If they conform to the convention that the DNS root servers practice, then
a dig query from several locations should suffice.  Choosing an anycasted
DNS root at random, you can do
	dig hostname.bind chaos txt
And the response should include a line like
hostname.bind.          0       CH      TXT     ""

>From other locations, it might be "" or somesuch.
If they don't do that, then you are stuck with more ad-hoc methods like
traceroutes from many different locations, or checking out AS-PATHS in
Routeviews and using your intuition.


Peter Boothe
PhD Student                         "Young man, you think you're very
Computer Science                    smart, but it's turtles all the way
University of Oregon                down!"

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