DCC server locations for anon clients

Vernon Schryver vjs@calcite.rhyolite.com
Thu Aug 15 23:55:41 UTC 2002

> From: Tim Wicinski <tim@meer.net>

> ...
> Remember, it's not geographical distance, but routers hops to your site.
> We reach one of our peers in TX just fine.

After network-distance, the speeds and loads of the servers matters.
That is why the DCC client code picks the IP address with the smallest
gross round trip time (RTT) including queuing and processing delays
to all of the servers listed in the client's map file.  Every hour or
two or when the current choice has become a lot slower, the client
code checks all of the known servers.

The first column of that table in the web page now contains links to
a CGI script that does `cdcc "host hostname; stats all; info"`
Those RTTs displayed by `cdcc "host...info"` are an instantaneous
measure of the overall speeds of the servers with "hostname" A records
as seen at www.rhyolite.com or www.dcc-servers.net, or wherever you
run the command.  The bald `cdcc info` command shows the long term
RTTs of the servers your client is using.

All of the IP addresses represented in that table could be announced
as a single FQDN.  However, that would introduce a single point of
failure.  If the DNS servers for that domain stopped working for
technical or other reasons, things would be broken.  

That suggests that you might want to put two or three of the FQDNs in
your map, and let the computer decide which server is faster tonight.

There is no harm in having the FQDNs overlap, because the DCC client
code notices and does the right thing.  Those who control the other
FQDNs are welcome to add (z.dcc-servers.net) to their
FQDNs.  Given permission I'd happily add to dcc.dcc-servers.net.

Recent versions of the source automatically generate a default map
file containing localhost and dcc.dcc-servers.net.  That means that
if your server is listed in dcc.dcc-servers.net, it will get at least
hourly traffic from many anonymous users, including the SpamAssassin
users who don't follow the bogus advice to replace dcc.dcc-servers.net
with dcc.rhyolite.com.

Vernon Schryver    vjs@rhyolite.com

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