OK just my 2p (lets see if anyone can see anything wrong here?)
one point first
if you install without DHCP running on your router Lmce will assign itself 2 iIP addresses 192.168.80.1
and internal 192.168.80.254
it cannot connect to the internet like this initiallly and brings it's own problems so
(again in my opinion)
assuming you dont need Lmce as a router device for your internet and you only want 1 NIC
here is what SEEMS to work out...
during install have DHCP on on the router WITH ONLY LMCE BOX CONNECTED!
once install is complete set up the WAN side to static at its current IP settings IE if your router is at 192.168.0.1 then set your LMCE ext IF to 192.168.0.254 then turn OFF DHCP server on the router...
now at your roter/switch you have 2 subnets available...
192.168.0.X original LAN and 192.168.80.X LMCE lan (with DHCP)
at this point if you want to share anything belonging to the LMCE LAN you must either turn off LMCE's firewall or configure it accordingly..
dont forget LMCE is INSIDE your existing firewall entirely so turning off LMCE's firewall should be fine
now.. anything you don't want to commit to LMCE's control should be set with a static IP in the subnet 19.168.0.X LMCE will not see nor try to control this
anything you want LMCE to use.. you enable DHCP on
that will end up on the 192.168.80.X subnet
this way both networks can share one switch and one lot a cabling and there should be no unwanted interaction
if you need to access something inside LMCE's subnet from your original network (say a NAS)
you can do so by it's IP address (or presumably it's DNS name) THROUGH LMCE's router
anyone see anything wrong with this solution??
(my background is in networking NOT Linux)
cheers
Gazzzman