Reverse lookups on local IPs

[Barry Margolin]

In article <9li9cc$j1e at pub3.rc.vix.com>, Jon Booth  <jon at lucidlogic.com> wrote:
>A while ago, about 2 years I think reverse lookups on local LAN IPs were
>working. ie nslookup 192.168.1.1 returned something (I can't exactly
>remember what though)
>
>Does anyone remember if it was a global setup or just my local (Telstra
>Australia) ISP's DNS server.
>
>It was very handy as it meant you didn't have to do the task yourself.
>
>Am I just talking trash or was it really set up by whoever controls those
>IP's (ICANN or whoever). Why don't the set it up again?

The machines that the RFC 1918 addresses have their reverse DNS delegated
to (blackhole.isi.edu and blackhole.ep.net) used to actually exist and
respond, although I believe the zone files were empty.  This would permit
you to get a rapid NXDOMAIN error, rather than a timeout.  I suspect they
took them down because they were getting hammered by many queries, and/or
they decided it would be better if folks found out that they didn't have
their private reverse DNS configured properly by making them suffer through
the timeouts.

When blackhole.isi.edu went away, we configured our caching nameservers
with empty zones for all the RFC 1918 blocks.  If you were getting actual
hostnames for this reverse DNS, either you had the reverse domains
installed on your internal servers and you filled it in with your local
machine names, or your ISP created reverse domains and filled them in with
dummy entries.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Woburn, MA
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