[ntp:questions] Interface IP address Change.

Frank Kardel kardel at ntp.org
Mon Jun 30 21:00:18 UTC 2008

David Woolley wrote:
> kiran shirol wrote:
>> Instead of using a polling approach, would it not be better we use a 
>> notification model, where in whenever there
> There is no direct event interface, because, when Berkeley sockets were 
> designed, interface addresses were fixed at system startup.  TCP was 
> designed for peer operation, which requires stable addresses, and DNS 
> was designed for very slow changes.

This statement needs to be refined slighly. The BSD stack has had for 
quite some time the routing socket interface. This interface allows to 
read notifications about network topology change events. While TCP 
requires stable addresses other protocols like UDP do not. NTP uses
UDP for communication and can perfectly cope with changes of local 
addresses since 4.2.4.
DNS is usually not troubled as the clients just get new addresses and 
thus just other DNS names, Stability of addesses is only required for 
servers. Having a server as moving target is not really fun.

There is, however, a weak spot in the reference implementation. It
resolves DNS names only once. This is problematic for slowly
(administratively) changing server addresses for long running client
daemons. This needs to be fixed in the future.

> What you are being told is that, on some operating systems, there is an 
> event interface for routing, which is dynamic, which provides enough 
> information to infer an interface address change.


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