[ntp:questions] Interface IP address Change.

Frank Kardel kardel at ntp.org
Sun Jun 29 20:40:04 UTC 2008

David Woolley wrote:
> Kiran Shirol wrote:
>> In one of my setups with just one interface I had configured ntp server.
>> Everything works fine till here. Now I change the IP address of the
>> interface
> Interface addresses aren't supposed to change, not just for ntp.  You 
> will probably also confuse named.
>> My question is How can I make NTP automatically detect this change and
>> rebind
>> upon the change in the IP address of the interface ?

Since 4.2.4 ntpd detects changed interface addresses. Depending on the
OS used this happens sooner or later. The fasted detection is on systems
that have the routing socket interface (*BSD and maybe Solaris). For
Windows and Linux interface scans are done every five minutes by 
default. This default can be changed with the -U <secs between scans>
command line switch for faster detects (60s is the current lower limit).

If some good souls from the Linux and Windows communities would
contribute the code needed the for fast detection on these systems 
reaction time would improve there.

> I believe some work has been done on working round broken ISPs who 
> deliberately, or otherwise, misoperate DHCP.

The dynamic interface update code was introduced in 4.2.4 to make
ntpd work correctly in dynamic/mobile environments.

   I'm not sure what state it
> is in, but you should certainly be using the very latest release 
> version, if not a development version.
4.2.4 (the current stable version) is just fine.

> You are, of course, welcome to submit a patch to the source code.


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