How to find the subnet and ip range on a blocked router

[pedropt]

ok this one is not easy , and frankly i have no clue how to get it .
Imagine that you buy an used router over ebay witch its configuration is :
-static ip (witch you have no idea the range of it)
- a different subnet config than 255.255.255.0
- reset option blocked in router configuration

now , you want to configure your network card to the router config so you can access its admin webinterface and change the static ip to dhcp , but you do not know either the subnet config or ip range .

Question : How it is possible to find this data ?

[rastamouse]

Why not just factory reset it? There's usually a reset button on the back somewhere, which, when held for a length of time (e.g. 10 seconds). You can then Google the default config for the make/model.

[pedropt]

Why not just factory reset it? There's usually a reset button on the back somewhere, which, when held for a length of time (e.g. 10 seconds). You can then Google the default config for the make/model.

what if the reset switch were you put the clip to restore the default config is disable .
you know that in some brands you can disable the manual reset of the device right ?
well , this is that case .

-static ip (witch you have no idea the range of it)
- a different subnet config than 255.255.255.0
- reset option blocked in router configuration

[rastamouse]

I've never seen that except for in DD-WRT, don't see why you would need that in a standard consumer router. Also, how do you know if you can't get into the config, just an assumption? Have you tried just plugging in and sniffing for random traffic? Or ARP scan, ping sweeps, possible hostnames etc?

[pedropt]

the issue is not for me , i don't have that issue .
i already also notice that using wireshark and disconnecting the device an reconnect again , the arp requests may reveal the ip range of the device , but not the subnet .
One of my router have static ip (i can access to it , is just for testing) , and i used dhcp to test wireshark and see if i could find the network config .
Guess what , nothing shouted from the router .

Static ip on a device could be good for protecting an intranet or a wifi ap , if anyone crack the wifi access password , it could be stuck in acquiring an ip to navigate .

[pedropt]

Well , i didn`t replied anymore to this thread because i forgot it .
The issue was that the router was configured as a switch , so , this particular modem router had manual reset option deactivated in settings .
I was able to make a reset to it by mistake without knowing .
Ususally when people want to reset their routers , what they do is they put a pin on the small reset orifice for a while and then the router blink all lights and reset is done .
Or , they press the reset button and unplug the power and plug again the power with the reset button pressed to make it .

These 2 options did not work .
To return the router (configured as switch) to its default settings as a modem router , i had to turn off the power plug , then turn it on , and wait for the bootload to start (power led change color) , when the power led changed color i press the reset button for a few seconds and the reset was made .

Because it was configured as a switch before , then i was unable to receive any arp requests or sub network info on wireshark , even if the case was a static ip configuration .