Multiple domains pointed to the same IP

[Jeff Cochran]

>>I understand that there can only be one entry in the PTR file which gives
>>one domain name for a given IP address when a reverse lookup is performed.
>
>>Does this mean you cannot have mutiple domains map to a single IP on the
>>Internet e.g.:
>
>>one.mydomain.com    -> 192.1.2.3
>>one.anotherdomain.com -> 192.1.2.3
>
>As far as I know, multiple PTR are legal, but usually not recommended.
>
>You can have multiple A or CNAME pointing to A for a name, but the PTR
>only needs to point to one name.  Usually I find one preferred name.

What about systems that check the reverse DNS to allow access, for FTP
for example?  If I have two domains:

foo.bar.com  192.1.2.3
foo.bar.net  192.1.2.3

but it would be the same 2.1.192.in-addr-arpa file with:

192.1.2.3  foo.bar.com

I would assume a reverse from foo.bar.net would go to foo.bar.com,
correct?

How about if the foo.bar.net entry was a CNAME to foo.bar.com?  Would
this correct the situation since the reverese would show foo.bar.com
with an alias of foo.bar.net?

Jeff