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<div class="moz-cite-prefix">On 22/11/16 02:19, Amos Shapira wrote:<br>
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cite="mid:CAF9n_WW=V43FgSvvVS34qZhrFHh0m1uYOZON2Rtpsc0wCjJZsg@mail.gmail.com"
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<div class="gmail_quote">On 21 November 2016 at 18:20, Shachar
Shemesh <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:shachar@shemesh.biz" target="_blank">shachar@shemesh.biz</a>></span>
wrote:<br>
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<div class="gmail-m_-7321374812641881217moz-cite-prefix">The
DNS resolving <a moz-do-not-send="true"
href="http://google.com" target="_blank">google.com</a>
guesses your gegraphical location, and gives you an
answer that is nearest where you are. If you use
another DNS to query the domain, you will get a
different IP:<br>
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<div>It's not always a "guess your geographic location". The
smarter ones use Anycast to advertise the same IP address
from multiple locations on the Internet and let BGP do its
magic to route your packets to the nearest server, taking
into account any congestion or other transient connection
speed changes. This is how Google's DNS 8.8.8.8 works, or
Akamai's CDN. The nice thing about it is that you get
optimal response even at the host resolution stage. The
DNS server can then take its knowledge of the DNS query
source address into account when it decides which IP
address to resolve to.</div>
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<div>It's pretty neat, personally I find it a fascinating
trick: <a moz-do-not-send="true"
href="https://en.wikipedia.org/wiki/Anycast">https://en.wikipedia.org/wiki/Anycast</a></div>
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It is, quite fascinating. It is not, unfortunately, as useful as you
make it out to be. Neither Google nor Akamai use it for web traffic,
for example.<br>
<br>
The reason is twofold. First, anycast is poorly equipted to handle
TCP connections. There is a (remote) possibility that the handler of
your IP would change mid-request, which would not play nice with
your connection.<br>
<br>
The second, more pertinent, reason is that , at least for Akamai,
they would like to be able to control which server you reach when
you make a request. The would like to be able to re-route your in
case something bad happens to that server. DNS TTL can be set as low
as 30 or 60 seconds. BGP routes have much longer settle times.<br>
<br>
Shachar<br>
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