Speeding up DNS change propagation

Danny Sinang d.sinang at gmail.com
Fri Sep 18 19:46:11 UTC 2015


Ah, many thanks ! :)

On Fri, Sep 18, 2015 at 3:37 PM, John Miller <johnmill at brandeis.edu> wrote:

> The .com nameservers don't know anything about ftp.example.com; they
> just know the nameservers for example.com.  So have no fear -- BIND
> will not cache an upstream response for ftp.example.com: you'll only
> hear about ftp.example.com from the example.com nameservers.
>
> Pretty much all upstream nameservers: root NSs, .com NSs, example.com
> NSs--are authoritative-only.  They don't cache or offer cached
> responses.  (Not 100% accurate, but nearly always so.)
>
> John
>
> On Fri, Sep 18, 2015 at 2:58 PM, Danny Sinang <d.sinang at gmail.com> wrote:
> > 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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> >>
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> >
> >
>
>
>
> --
> John Miller
> Systems Engineer
> Brandeis University
> johnmill at brandeis.edu
> (781) 736-4619
> _______________________________________________
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