Understanding my network

[Dale Dellutri]

On Thu, Aug 30, 2012 at 8:11 AM, Frank Pikelner
<frank.pikelner at gmail.com> wrote:
> On Wed, Aug 29, 2012 at 3:40 PM, Arthur Dent
> <misc.lists at blueyonder.co.uk> wrote:
>>...
>> 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...
>>...
>
> 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.
>...

I must respectfully disagree with this.  This situation should be handled by a
router/firewall correctly.  If a device internal to the lan sends a
request meant
for the router/firewall's external ip address, the router/firewall
should recognize
its own external ip address and deal with it internally, correctly.

The fact that a reboot of the router/firewall solved the problem shows
that this is
true.  I assume that the reboot solved it because it cleared out some old, stale
ARP and NAT/NPT tables.  I'd be curious to hear if this will work the next time
the router/firewall gets a new (dynamic) external ip addr, or whether it will
then require another reboot.

-- 
Dale Dellutri