[ntp:questions] Interface IP address Change.

kiran shirol kiran.shirol at gmail.com
Tue Jul 1 04:07:11 UTC 2008


That would be good so that the user need not have to worry about any changes 
in the IP addresses in
future. I read some other mail thread on the forum and the solution 
suggested was to restart NTP. But
that approach needs user/admin intervention and thus not a good thing to do. 
I will keep a watch on the
bug IDs too.

Thanks Frank for the responses.


"Frank Kardel" <kardel at ntp.org> wrote in message 
news:48694671.8010207 at ntp.org...
> Kirian,
> the core for the dynamic interface code *is* actually event based.
> ntpd listens to routing messages on the routing socket. The routing socket 
> has been part of BSD and BSD derived stacks for quite some time.
> Whenever a routing message that indicates a possible routing change
> is received a rescan is started within two seconds. This approach is
> even better than just watching interface changes as it detects changing
> routes for peer associations on the fly.
> Unfortunately the BSD routing socket API is not available in every OS. 
> Linux has a similar but different mechanism. Windows has another. For 
> these systems ntpd currently uses the periodic scan approach to pick up 
> changes.
> Thus there are two bugs waiting to be closed:
> 1) Windows: https://support.ntp.org/bugs/show_bug.cgi?id=991
> 2) Linux: https://support.ntp.org/bugs/show_bug.cgi?id=992
> For these and other operating systems not supporting the BSD routing
> socket interface a small piece of code is needed to support event driven 
> re-scans.
> I am still waiting for people to provide the respective patches....
> Frank
> kiran shirol wrote:
>> Frank,
>> Instead of using a polling approach, would it not be better we use a 
>> notification model, where in whenever there
>> is a change in the IP address a notification be generated from the 
>> interface managing module. I am not sure if
>> there is such a facility availble currently, I will check the same a get 
>> back.
>> My point is , the probability of change in the IP address is low and 
>> hence periodic polling may not be the best
>> approach. Let me know your comments.
>> Thanks
>> Kiran
>> "Frank Kardel" <kardel at ntp.org> wrote in message 
>> news:4867F324.7080506 at ntp.org...
>>> 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.
>>> Frank

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