How to see the gateway ip adress on a router that you cant connect to ? (TP-LINK)

So... I know its dumb, but, long time ago, about 4 years or something I moded this TP-LINK and got it to work as a router to connect from my ethernet to the wifi... Thing is, I stopped using it because it was having issues with my old modem, now I wanna try it again and cant connect to it... How to a I get to know the IP adress I used etc? (BTW I cannot reset it or anything, the buttons dont work anymore..)

Should I just install the firmware again ?

The first step would be, assuming you have OpenWRT/LEDE loaded on it, to try to get it into "failsafe" mode. Directions are on the OpenWRT wiki for most supported devices.

If you re-flash it, you will almost certainly lose any configuration you had on the device.

I'm pretty sure I have OpenWRT, it was the only thing back them, I look the wiki up, thanks

Another approach, if the buttons won't get you into failsafe mode, would be to see if you can either get a DHCP address from the router by attaching to its LAN side, or see if you can give the router a DHCP address on its WAN side from a different DHCP server (by plugging it in to your network on its WAN side).

In the first case, you can try to ssh into the box at the .1 of the subnet assigned by the router to the attached host. In the second case, you'd have the address assigned to the router by looking at your DHCP server's log or other state information. "Ancient" versions of OpenWRT might still enable telnet.

Can't help with "breaking" a password you might have assigned to the router. You'd need to get it into "failsafe" mode to change that.

I see, the only thing I need to know is the IP adress of the router... xd

...and the "root" password, unless you're in failsafe mode

the password is probably my basic throwaway pass

I guess I will just try a few numbers I usually use as IP, I only tried 3 so far

If the firmware running on the router has IPv6 capability you can also try to access it by its IPv6 link local address.

Connect your PC / Laptop ethernet cable to one of the TP-Link lan ports, then on your PC / Laptop issue a ping6 ff02::1%eth0 - replace "eth0" with the appropriate interface name if needed.

You'll see output similar to this:

jow@jow:~$ ping6 ff02::1%eth0
PING ff02::1%eth0(ff02::1%eth0) 56 data bytes
64 bytes from fe80::6666:b3ff:fe47:e1b9%eth0: icmp_seq=1 ttl=64 time=0.046 ms
64 bytes from fe80::20d:b9ff:fe35:8849%eth0: icmp_seq=1 ttl=64 time=1.44 ms (DUP!)
--- ff02::1%eth0 ping statistics ---
1 packets transmitted, 1 received, +1 duplicates, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.046/0.745/1.444/0.699 ms

One of the two IP addresses is the router, the other one is the PC you're pinging from. With a bit of luck, you should be able to SSH to it:

jow@jow:~$ ssh root@fe80::20d:b9ff:fe35:8849%eth0

BusyBox v1.26.2 () built-in shell (ash)

    /        /\      _    ___ ___  ___
   /  LE    /  \    | |  | __|   \| __|
  /    DE  /    \   | |__| _|| |) | _|
 /________/  LE  \  |____|___|___/|___|            
 \        \   DE /
  \    LE  \    /  -----------------------------------------------------------
   \  DE    \  /    Reboot (SNAPSHOT, r4497+16-a73471dea7)
    \________\/    -----------------------------------------------------------

root@jj:~# ^D
Connection to fe80::20d:b9ff:fe35:8849%eth0 closed.

you could also use ip neigh and compare the mac address on the device label