Understanding my network

[Frank Pikelner]

On Wed, Aug 29, 2012 at 3:40 PM, Arthur Dent
<misc.lists at blueyonder.co.uk> wrote:
> Hello all,
>
> I am part-way through a bare-metal rebuild of my small home server (it
> was F15, I am rebuilding as F17). This machine serves up my IMAP mail
> with Dovecot and Squirrelmail and hosts my small (mainly static)
> website.
>
> The machine in question sits on my home network at 192.168.2.2. I have
> opened port 993 on the firewall. I have a domain name (let's call it
> example.org) with dyndns.org which points to my IP address (let's call
> that 123.456.789.123) and my router forwards port 993 to 192.168.2.2.
>
> So here's the thing - and I don't remember having this problem with F15
> (or previous):
> I can access my mail using a client on another machine in my network if
> I configure it to use 192.168.2.2, but for my mobile devices I configure
> the email client to point to example.org. If I am outside of my network
> they can access mail fine, but if I am at home and they are connecting
> via my own wi-fi... no joy...
>
> The same by the way is true of SSH. Although I use a non-standard port
> for SSH the principle is the same.
>
> I have obviously messed up or missed out some configuration step, but I
> can't understand where I have gone wrong.
>
> Can anyone help me to fix this?
>

Mark,

Your issue is likely at your firewall - firewall does not typically
allow something like this. If you're accessing your mail servers using
an external IP (DynDNS) while you are connected to the inside portion
of the network (private IP), this will not be permitted by your
firewall. You are essentially going out to the firewall (for the
external IP) and coming back in as the firewall already owns the
external IP - to access and internal mail server.

To overcome the problem one possible solution is to have a DNS server
on your network (your client needs to have it assigned with DHCP) with
the mail server entry with the private IP of your mail servers and
your mail client use the internal DNS server for name resolution (for
all other entries the DNS server would relay to an outside DNS).

Therefore, when you are inside your network you get the private IP for
your mail server and when outside you get the public IP from DynDNS.

Hope this helps,

Frank