Re: [Ddclient-support] DDClient Detecting a Second Gateway (Provider)???

[Ingo S. <isc...@as...>]

Hi Larry,

i admit i didn't look at the captured packets,
but the following explanation looks plausible in general:

Larry Houston wrote on Wed, Feb 03, 2010 at 03:55:41PM -0500:

> possible explanations as to why this Asymmetric Routing has occurred?

Usually, DNS changes do not take effect immediately.
It is very common to employ caching on DNS servers.
Sometimes, it takes up to a full day until some caches expire.

Thus, if you change DNS information on the DynDNS server,
some servers may pick it up fairly quickly, but some others
may take more time.  In your case, even very small delays can
make a difference.

In general, the routing of a response IP packet does not depend
on the routing of the packet it responds to.
Thus, if you send a packet via the new route to a host using a caching
DNS server still having your old IP address in its cache, the response
packets will arrive via the old route, possibly triggering another switch
of the address you have registered with DynDNS.

Again, this is just one relatively simple, plausible explanation.
The real effects may be more involved; both DNS and routing can be
quite tricky.

In any case, i think combining "use=web" in your ddclient configuration
with multiple Internet uplinks is asking for trouble - in fact, just
the trouble you are experiencing, unstable DNS and routing.
The "use=web" method may be sufficient for trivial setups,
but it's not that useful once things get more complicated.
You might wish to look at other configuration methods;
as i said, there are plenty.

So far, i see no indication that you suffer from a bug in ddclient.

Yours,
  Ingo

--
Ingo Schwarze <isc...@as...> | Software Engineer | Framework Team
Astaro AG | www.astaro.com | 76227 Karlsruhe | Germany