I'm not clear on what setup your trying to achieve.
The thecus is like a pc with two network ports. You can configure it to route but dont expect it to work like a switch.
The dual network ports idealy would offer load balancing and failover for a single ip address which is the intended purpose of the ip sharing.
Unfortunately ipsharing has "issues"
I personally run all of my computers on one subnet 192.168.1.xxx
I have no valid reason to run multiple subnets. I have a router for routing.
Prior to 2.1.03 you could set both network ports to the same subnet. For name based file shares this worked well as a failover mechanism.
Digging through the html and php code i noticed that Thecus are working on including a PPPOE client and a routing option.
This seems to parallel the n5200 functionality.
As part of this philosophy the've stopped allowing people to set both ports on the one subnet.
Given that the routing functionality isn't yet enabled applying the restriction is pointless.
Here's the bit that makes it really stupid. If you've got a dhcp server set both ports to use dhcp and they'll both end up on the same subnet.
Here's the other thing. The cpu in the n2100 is just powerful enough for it's current tasks. Ask it to perform as a router (with suitable firewall) and you're asking for performance problems.
If you want both ports to be in the same subnet then here's the process...
Decide what network structure you want. If you need a switch then use a switch. Most good DSL and cable routers today have built in switches although usually just 10/100.
Gigabit switches do improve performance.
If you need a router then get a router. The thecus just doesn't have the power.
Decide what ip address you want for each port. Set port 2 to something different in a different subnet. Enter the 255.255.255.0 subnet mask.
Set port one to the final ipaddress that you want for it.
Apply and reboot etc.
Log in with ssh and use vi to edit /app/cfg/cfg_nic1 (this is the file for port 2)
You only need to change the ipaddress.
If you reboot now your job is finished because the thecus will now be running with each ports having the correct ip address.
If you look into the web gui you will notice that it's telling you the wrong ip address. That's because the web gui gets the value from the database and not from the config file.
This update statement will update the value in the database to whatever you choose to insert.
sqlite /app/cfg/conf.db "update conf set v='192.168.1.x' where k = 'nic2_ip'"Theoretically you could put what you want in there or leave it with what it's got indefinately. As far as the OS is concerned it's happily using the values in
/app/cfg/cfg_nic0 and
/app/cfg/cfg_nic1 It couldn't care less what the gui says...
If you want to play with expanded subnets then there are online subnet mask calculators out there (or there used to be) which you should use.
If you need advice on achieving a specific configuration then you'll need to supply more info on your intended network topology.
I feel that the product planner who included this restriction should be sat in the same corner as the one who put the mac files in the smb veto list and told to be quiet.
Perhaps though when the pppoe is finished it will all make a little more sense.