strange ping and traceroute results

[Amos Shapira]

Anycast is not suitable for TCP.
It IS fantastic for DNS (which uses UDP), which is the first thing a client
does most of the time to find the server.
Akamai control server groups by allocating per-customer per-object host
names, then these can be resolved using their very highly customised DNS
servers to the right server (also taking into account dynamic changes like
server cluster load or failure).
Since DNS uses UDP and the traffic consists on one packet in each
direction, Anycast is ideal for that scenario.
The actual content transfer (e.g. move streams, which is where I with
Akamai for stan.com.au) doesn't use Anycast.

On 24 November 2016 at 04:06, Shachar Shemesh <shachar at shemesh.biz> wrote:

> On 22/11/16 02:19, Amos Shapira wrote:
>
> On 21 November 2016 at 18:20, Shachar Shemesh <shachar at shemesh.biz> wrote:
>
>> The DNS resolving google.com 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:
>>
>
> 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.
>
> It's pretty neat, personally I find it a fascinating trick:
> https://en.wikipedia.org/wiki/Anycast
>
> 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.
>
> 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.
>
> 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.
>
> Shachar
>



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