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.sin...@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 <johnm...@brandeis.edu> wrote: >> >> On Fri, Sep 18, 2015 at 2:35 PM, Danny Sinang <d.sin...@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 >> _______________________________________________ >> Please visit https://lists.isc.org/mailman/listinfo/bind-users to >> unsubscribe from this list >> >> bind-users mailing list >> bind-users@lists.isc.org >> https://lists.isc.org/mailman/listinfo/bind-users > > -- John Miller Systems Engineer Brandeis University johnm...@brandeis.edu (781) 736-4619 _______________________________________________ Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe from this list bind-users mailing list bind-users@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-users
