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<LI class=title><A href="http://www.dyndns.com/developers/">Developers'
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<H2>Detect IP Changes</H2>
<P>To determine whether a client should update, it must have a reliable method
to determine what its current IP address is so it can compare the current
address to last updated address. There are two methods.</P>
<H3>Directly Connected</H3>
<P>A client may determine, automatically or through the input of the user, that
it is directly connected to the Internet. The device would have a publicly
addressable IP address. In this case, the optimal method is to use API methods
from the parent operating system's network stack.</P>
<H3>Web IP Detection (CheckIP)</H3>
<P>A client may determine, automatically or through the input of the user, that
it is not directly connected to the Internet. The client is on a machine with a
private IP, usually on <A href="http://rfc.net/rfc1918.html">RFC 1918</A> space
(10/8, 172.16/12, 192.168/16). In this case, the optimal method is to use web IP
detection.</P>
<P>DynDNS operates a <A
href="http://www.dyndns.com/developers/checkip.html">CheckIP service</A> which
may be used with clients that work with DynDNS.</P>
<H3>Complications</H3>
<H4>Initialization</H4>
<P>When a client starts for the first time, it is expected that it will perform
an update when it is first enabled. This may result in a <CODE>"nochg"</CODE>
return code which increments an abuse counter. Great care should be taken to
prevent initialization unless it is necessary.</P>
<P>It is expected that the IP address will be stored in a non-volatile manner.
This is especially true for hardware based devices.</P>
<H4>Multiple Interfaces</H4>
<P>Some clients can be installed on devices with multiple network interfaces,
such as a gateway or router. If this is the case, the developer needs to base a
basic assumption or the user needs to be given the option as to which interface
to use for IP detection.</P></DIV><BR clear=all><!--htdig_noindex-->
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