Re: lists of DNS servers by region.

[Valdis.Kletnieks () vt edu]

On Thu, 12 Dec 2002 14:42:08 EST, Haesu said:
> > Many DNS "load balancing" solutions will return the address of the web
> > server closest to the _query source_.  This means these systems work best
> > when your recursive DNS servers are topologically closest to your users.
>
> Correct me if I am wrong.. But..
>
> I don't think multiple 'A' record load balancing will return the IP
> address of the web server that is closest to the _query_source_. If this
> is true, then Akamai has reinvented the wheel with their near-by DNS
> setup on *.g.akamai.net entries.

Akamai doesn't use the usual round-robin.  They do OTHER magic.

Some solutions use a special magic DNS backend that will launch a PING or
other RTT detector from the multiple service locations, and then return the
location with the lowest RTT.  Of course, this means you're measuring the RTT
from the servers to the user's DNS server - if they're using a DNS server
that's a long way away network-wise, this can produce odd results.

The problem is that the backend doesn't know the source of the original query,
they only know the IP address of the DNS server that's doing the recursion.
-- 
                                Valdis Kletnieks
                                Computer Systems Senior Engineer
                                Virginia Tech

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