I am pretty sure that this Zyxel GS1900-8H (no P) got openwrt installed a few years ago and was unused then. A network scan doesn't find it, so it has probably another network assigned or DHCP is disabled.
What happens, if openwrt is installed and I press the reset-button with a needle?
I have no idea what is installed. This device has 2 flash partitions.
It will not reset on its own, but you can use the reset button to enter failsafe mode. From there, you can reset the device to defaults or fix the configuration. \
So if there is no openwrt installed, a reset should work, but this is very unlikely that the original firmware is installed.
What does this mean? It is no problem if the openwrt configuration would be set to default. I am pretty sure there was not much configured.
Sets the failsafe mode the IP to 192.168.1.1 and DHCP? That would be fine.
I never used this, so the 1st step is to know the correct network. I am unsure too, if I know the password for openwrt. It is a long time ago, that I played with this device
I would start by using the reset button as described in the user guide from the manufacturer. Then try to connect to the device at the default address that is listed in that guide. If this works, that indicates that the device is running the original vendor firmware. If it doesn't....
Then try failsafe mode which will work if OpenWrt is installed.
you can reset the config once in failsafe mode by issuing firstboot -y && reboot.
There is a good choice, that it has openwrt installed, because I found from 2021:
Failsafe mode starts the router with the IP address 192.168.1.1, and disables DHCP
The openwrt-version is very old and I want to install 25.12.5
There are 2 versions:
Zyxel GS1900-8 A1 and B1. Is the differnce the partition which is flashed?
Correct.
No. This would be different hardware versions.
How can I find out which hardware version I have? Can I see this with failsafe mode?
Can I use "scp -O" to copy the openwrt-image to /tmp in the Zyxel in failsafe mode?
I would like to copy the image to the Zyxel and then use "sysupgrade -n". Is this okay with failsafe mode?
With routers I add normally:
arp-scan iperf iperf3 nmap openssh-sftp-server rsync rsyncd
Does any of these make sense with the switch? At least I need ssh.
It looks like I found the network.
$ nmap -sn 192.168.1.0/24
Starting Nmap 7.98 ( ``https://nmap.org`` ) at 2026-07-04 23:55 +0200
Nmap scan report for 192.168.1.1
Host is up (0.0027s latency).
This is the manual configured pc:
ifconfig -a
enp1s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.146 netmask 255.255.255.0 broadcast 192.168.1.255
So the other must be the Zyxel, but 192.168.1.1 cannot be found with Firefox.
Is there a way to check if openwrt is installed now?
Usually this is found on the info sticker on the bottom of the device. Otherwise, try ubus call system board
Yes.
No. And ssh is already included.
This is expected. The web server does not run in failsafe mode. You need to use ssh.
I didn't use failsafe mode, just guessing and trying this network.
ssh root@192.168.1.1
ssh: connect to host 192.168.1.1 port 22: Connection refused
If there would be Zyxel FW the webserver would answer, as well as the openwrt-webserver.
And it is very unsure, if the ssh-password works, which I know.
Did you disconnect all other network cables except for just one ethernet connection between your computer and the GS1900-8H? You also need to disable wifi on your computer. This is to make sure that you can guarantee that the device to which you think you are connecting is the only device that could possibly respond.
Yes
The pc is a minipc with 1 ethernetport and this is connected to the switch. No other cables are connected or plugged in.
Always done.
$ nmap -p- 192.168.1.1
Starting Nmap 7.98 ( https://nmap.org ) at 2026-07-05 00:29 +0200
Nmap scan report for 192.168.1.1
Host is up (0.049s latency).
Not shown: 65533 closed tcp ports (conn-refused)
PORT STATE SERVICE
80/tcp open http
443/tcp open https
Nmap done: 1 IP address (1 host up) scanned in 78.35 seconds
Can I try something from the terminal?
http://192.168.1.1/cgi-bin/luci/
404 Not Found
The requested URL /cgi-bin/luci/ was not found on this server.
Not sure why I see luci, it is expanded automatically when entering the ip only, but maybe it is a result of the last openwrt-device.
Note this must be a very old openwrt, i discussed it 5 years ago.
What is the address of your PC right now?
Nothing changed.
try http://192.168.1.1 (specifically omitting the stuff beyond the address)
it always expands to http://192.168.1.1/cgi-bin/luci/
I will install another browser, so it was never used.
If the installed version of OpenWrt is very old (hint-hint-hint, don't lag behind the current stable version, if you want to have it easy), you may still need VID 100 on lan1 to connect.
The gs1900-8 has 3 Philips head screws and a nicely accessible 3.3V(!) UART header onboard (labelled, but not quite correctly, switch rx/ tx). If you are impatient.
Only recent (25.12.x and up) versions of OpenWrt can really distinguish between A1 and B2, the A1 version will run 'everywhere', but -if your SOC is recent enough- the B2 version is a bit more efficient.
I think the browser cache is fooling us.
I installed chromium and it opens with 192.168.1.1 the zyxel webif. So it looks like I have another GS1900 with openwrt installed years ago.
Sorry for asking.