Reverse DNS and single IP address space

[Jaime]

On Thu, 27 Mar 2003, James Earl wrote:
> Or, do I even need to worry about reverse DNS entries since my ISP
> already has them setup?

	They have probably done the reverse lookup already.  IIRC, the
reverse DNS for a single IP address can not be handed off to you by the
ISP without some interesting tricks.  The ISP that my job uses allowed us
to do reverse DNS for our 16 IPs, but they did some interesting tricks
with CNAME records to do it.

	The catch of this is that the reverse and forward lookups are
unlikely to match.  For example, you might want www.example.com -->
1.2.3.4 and 4.3.2.1.in-addr.arpa --> www.example.com.  However, the ISP
has already set up 4.3.2.1.in-addr.arpa --> customer15.dialup.isp.com.
This would mean that your DNS wouldn't be
www.example.com-->1.2.3.4-->www.example.com (as it should be) but would be
www.example.com-->1.2.3.4-->customer15.dialup.isp.com.  This isn't tragic
in most situations, but its not perfect.

	Talk to your ISP for details.

							Good luck,
							Jaime