Speeding up DNS change propagation

John Miller johnmill at brandeis.edu
Fri Sep 18 18:51:39 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 ?

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.


More information about the bind-users mailing list