Sorry for being off-topic since this is not quite programming related but more structure related. I have a network at home containing an ADSL router (with dhcp server; not disablable), a switch, an wlan access point (with dhcp server; disabable) and several machines. Due to some circumstances, I have the DSL router and the switch on the second floor of my house and the wlann access point on the ground floor. They are linked like this :

   ADSL router  (192.168.1.1)
       |
       +--> Comp1 (192.168.1.2)
       +--> Comp2 (192.168.1.3)
       |
       |
       +--> WLAN AP (192.168.1.5 due to ADSL router; 192.168.123.254 for the sub-lan)
               |
               +--> Comp3 (192.168.123.100)
               +..........> Laptop (192.168.123.101)

The ADSL router has a fix IP, the 192.168.1.2, 1.3 and 1.5 are DHCP. 192.168.123.100 and 123.101 are DHCP, too, but this time handed out by the WLAN Access point whose 123.254 is fix. My problem : The 1.x are not visible from the 123.x sub network. Is there any way to access the subnet ? I've tried to reconfigure the WLAN AP to disable the DHCP server but I cannot access anything after I did this. Does anyone have an idea what to do ?

I haven't any option where I can disable the DHCP server on the ADSL router.

I don't really need two networks. In fact, I would like to have just one. Unfortunately, I cannot put the wlan AP on the second floor of my house. If I do that, I don't have a connection on the ground floor.

So I had to put the AP on the ground floor and keep the (old switch) on the second floor.

I tried to disable the dhcp server in the wlan AP and I tried to set the IP of the wlan AP to the 192.168.1.x domain but then I can't get an connection to the AP from any computer on the ground floor that is connected to the AP (through wire or not).

Your wireless AP needs to be set into "bridging" mode.

Depending on the model, you do it different ways. However, one way that works most of the time is to hook up the AP to the main network using the same network ports as other computers, and leave the "uplink" port alone. Then force the wireless AP to a specific IP within the subnet, that you won't use as DHCP. 192.168.1.254, for example.

If your ADSL router/switch doesn't have reversing ports, you can use a cross-over cable to go from the ADSL router to the wireless AP.