[Ovmsdev] Firmware 2.8.1

[HONDA S-2000]

On Sep 24, 2015, at 5:46 AM, Collin Kidder <collink at kkmfg.com> wrote:
> On Thu, Sep 24, 2015 at 5:38 AM, Michael Balzer <dexter at expeedo.de> wrote:
>> I just checked the DNS record for tmc.openvehicles.com:
>> 
>> tmc.openvehicles.com.    14399    IN    A    54.197.255.127
>> 
>> I suggest reducing the TTL to 1 hour before we recommend the change to
>> users.
> 
> Keep in mind that much of the internet is ruled by caching name
> servers that will be quite stubborn about having to update their
> records. I seriously doubt that a TTL of 1 hour will be honored by
> much of anything. You're lucky if the ISP name servers bother to check
> for updates more than once or twice a day.

I'm fairly certain that there are no caching servers that ignore TTL. It would thwart emergency services if short TTL values were ignored. My ISP has changed my server ip address only once, and they went through the same process of shortening the TTL before the scheduled change, then increasing it back to normal after the new ip address was activated.

The catch is that any change does not take effect until the old TTL expires. The "14399" above is 4 hours. So, if the TTL were changed to 1 hour, it would not take effect on all caching servers until 4 hours later. At that point, though, all DNS servers would be working with a TTL of 1 hour. The typical is more like 24 hours, so the 4 hour entry above is rather short. If 24 hours were used, then the ISP would need to start the process 24 hours early by changing the TTL to 1 hour a whole day in advance of the ip address change. But at long as you know the current TTL and plan ahead, it's always possible to make a prompt transition.

Those name servers that only bother to check once or twice a day are doing exactly as they're told, and will check every hour if told to do so instead.

Brian