Speeding up DNS change propagation

[Danny Sinang]

As a follow-up to your answer for question #2, after my clearing the cache
or restarting BIND, won't BIND find an old cache of "ftp.example.com" in
the ".com" top level DNS server ?

Regards,
Danny

On Fri, Sep 18, 2015 at 2:51 PM, John Miller <johnmill at brandeis.edu> wrote:

> 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 ?
>
> Whatever TTL you have cached when the vendor makes the switch is how
> long it'll take for your caching servers to pick up the change.
>
> >      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 ?
>
> If you want to know the full TTL, ask the company's NSs directly -
> authoritative servers only give out the full TTL.
>
> > 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) ?
>
> Sure can.  Depending on your BIND version, you can also run rndc
> flushname <name> and it'll clear just that name from your cache.
>
> If the TTL is very long, don't forget about client-side caching as
> well.  Windows and OS X cache DNS lookups by default.
>
> John
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