Speeding up DNS change propagation

Bob Harold rharolde at umich.edu
Fri Sep 18 19:56:55 UTC 2015

On Fri, Sep 18, 2015 at 2:35 PM, Danny Sinang <d.sinang at gmail.com> wrote:

> Hi,
> Our vendor is changing their FTP server's IP address tomorrow.
> 1. How can I tell how long their DNS change will propagate to us ?
>      a. Do I just run dig a "ftp.example.com" and look for the TTL for
> that DNS entry ?
>      b. Every time I run that command, the TTL is shrinking. How do I find
> out the full TTL for it ?
> 2. Can I just restart BIND tomorrow to clear its cache and force it to
> query the "example.com" name server for "ftp.example.com" (so as not to
> wait for the propagation to reach us) ?
>      - BIND is not set up to be a Forwarding Server
> Regards,
> Danny

If the vendor would change the TTL on that DNS record to something short
(like 5 minutes?  'short' is a relative term) ahead of time (by at least
the current TTL), then the change would reach all users quickly, without
you or anyone else having to do any work.  Once everything is verified
working (could wait for the next business day), then the TTL can be changed
back to 'normal'.  This also helps them to be able to recover quickly if
something goes wrong.

Bob Harold
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