ST516 (bridge) + RT N66U questions

[rick155]

My current situation:

*****
Modem
*****

Speedtouch 516 (bridge mode)
web interface: 192.168.1.254 and 10.0.0.138
Official firmware (latest)

*****
Router
*****

Asus RT N66U (PPPoE)
web interface: 192.168.2.1
DHCP: 192.168.2.2 <--> 192.168.2.254
Official firmware (3.0.0.4.374_720)

                               <---LAN---> PC
ST516 <---WAN---> RT N66U ---< 
                               <---USB---> External HD

I need to share the external HD so that from outside LAN I can access it.
I have already activated AiDisk and FTP.
Everything works with flawlessly as long as router has public IP

Now I have noticed I cannot access modem web interface anymore because destination is unreachable

I have tried moving router to 192.168.1.2 (so that both router and modem are in the same subnet) but still the destination is unreachable

Now my questions:

1) Is this due to the the fact that LAN and WAN ports are separated so, even in the same subnet, I am not able to reach a WAN ip from LAN ip ?

2) Searching on internet I found there are two possible tricks to see modem web interface are:

a) Loopback

                      ---------------------------------
    _________________ | ___________                   |
    |               | | |         |                   |
    |               | | |         |                   |
---------     ---<LAN ports> <WAN port>---      -------------
|       |     |                          |      |           |
| Modem |     |          Router          |      |     PC    |
|       |     |                          |      |           |
---------     ----------------------------      -------------

This way modem is connected to LAN port and I should be able to access it, but I am not sure about these:

a1) is there a security problem if I let modem connect to all LAN ports ? Aren't all router's security measures (NAT/Firewall/etc.) bypassed ?

a2) using this configuration can I keep modem in bridge mode ? I need router to keep public ip otherwise, with modem in routed PPPoE, router will have internal IP and I won't be able to access disks from outside

b) modify routing tables so that WAN IP can be reached from LAN IP

b1) Is it possible to achieve this with official firmware ?
b2) are there any security risks in doing that ?

3) Previously I was running this configuration:

Modem (Router PPPoE)
Router (DHCP)

I was able to access modem web interface but, since my router had internal ip, I could not see it from outside and, by consequence, also external hd was not accessible.

Are there any settings I can change so that I can access disk from outside using "double NAT configuration" ?

Thanks

 

[rick155]

anyone ?

I know the topic is not the most interesting one, but I am sure many of you have a similar/identical configuration

please share with me how you were able to make it work