[dns-operations] anycasting for fun and profit

paul vixie paul at redbarn.org
Tue Oct 16 12:33:11 UTC 2012

dns anycasting can also be done solely with provider-assigned space and
no ASN of your own. for ISC we have three anycast clouds, one for f-root
which has its own prefix and its own ASN, one for our public benefit
secondary service which has its own prefix adjacent to f-root, and one
for our commercial secondary service which uses provider-assigned
address space for each named server.

the advantage to using provider-assigned space is that the global
routing table carries no separate burden on your behalf. i call this
"green networking" since it's more ecologically friendly. the
disadvantage is that if you want to change providers you have to
renumber. renumbering in this case isn't all that painful since you are
in control of the NS target name. there's a description at

note that the term "anycast" is sometimes overloaded to mean "DNS CDN"
where each server decides what answer to give for an A or AAAA request
based on that server's current guess about the client's locality
relative to various web farms. if the original question is really about
that, then the answer will have to go beyond routing policy. (ISC does
not do this, so my description above does not cover it.)


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