[Mimedefang] MX -> 127.0.0.1

[Kevin A. McGrail]

New version  now at
http://www.pccc.com/downloads/MIMEDefang/contrib/check_primary_mx_stub.pl
which takes into account much more of the cases you stated.  Thanks for the
feedback and I've added some comments inline below.

> Comment: not sufficiently general

I've added a function called invalid_mx to make this more general.

> Failing 127.0.0.1 and 0.0.0.0 is a good start... but there's all kinds of
invalid IP assignments that are being missed.  How often are they used?  I
don't know.
>
> I believe there are some generic perl functions written along the lines of

I think I can avoid this with the use of regexp's.

> Intranets only:
> 10/8
> 172.16/12
> 192.168/16

I disagree with bouncing these but I've put the code in to allow for the
user to decide.

> DHCP auto-discover:
> 169.254/16
>
> Localhost:
> 127/8
>
> Multicast:
> 224/8 through 239/8
>
> IANA reserved:
> 0/8 # probably forever
> # various others probably temporary
> 255/8 # probably forever

Implemented all of these except I did not go with the temporary ones.

> Checking the IP against all of these "bad" subnets is probably cheap
computationally, as the expensive part is getting the DNS lookup in the
first place.

I agree.  The problem is ensuring they are all bad and they stay bad.  I
chose the ones I felt were just absolutely unlikely to change.

Regards,
KAM