Zyxel USG Flex 100 — login, gateway address and status lights

Name: Zyxel USG Flex 100
Brand: Zyxel

Open a browser on a device connected to your Zyxel USG Flex 100 and go to 192.168.1.1, or myrouter.local.

The documented default login is admin with the password 1234.

Before you reset anything: a lost admin password on this model cannot be recovered. A factory reset is the only way back in and it erases the entire configuration.

The Zyxel USG Flex 100 is a firewall router from Zyxel, in UK use 2020-present. This page covers the four things people actually come looking for: its settings address, how its login works, what its lights mean and how to reset it safely.

What is the Zyxel USG Flex 100 gateway address?

The Zyxel USG Flex 100 settings page is at 192.168.1.1. Type that into the address bar of a browser — not into a search box, which will just search for the number instead of opening the page.

You can also use myrouter.local, which reaches the same page and is easier to remember.

Your device has to be connected to the Zyxel USG Flex 100 itself for this to work — over its Wi-Fi or by cable. On mobile data, or connected to a different network, the address goes nowhere.

Over HTTPS — Zyxel says the device "automatically routes this request to its HTTPS server, and it is recommended to keep this setting". Current firmware also answers on myrouter.local, which the older guide does not mention. The exception to watch for: if the unit has been adopted into Zyxel Nebula Control Center, Zyxel lists the login address as the address NCC assigned, and 192.168.1.1 may simply be wrong for that unit.

What is the default username and password for the Zyxel USG Flex 100?

Documented default — check the label too

The manufacturer publishes a default login for the Zyxel USG Flex 100, but it is worth checking the unit before you rely on it:

Username: admin
Password: 1234

Check the unit as well. Zyxel refers to "the Zyxel Device label" without saying which face of the case it is on, so we are not going to guess. A label definitely exists — Zyxel tells you to read the hardware revision off it — but its position is undocumented for this model. If there is a sticker, the value printed on it wins.

Try admin and 1234 first, and check the label before you conclude the unit has been configured. The reason for the hedge is that Zyxel's own current guide disagrees with itself. The front matter of the V5.42 guide says "Password See Zyxel Device label or 1234", while the body of that same document says twice that the default is 1234 — including in the reset description, which is the most load-bearing statement of the three because it describes what state the unit is in after a factory reset. The 2020 edition of the guide says 1234 with no ambiguity at all. Our reading is that 1234 is right for this model and that the "or label" wording leaked in because the V5.42 guide is shared across the FLEX 100, 100AX, 100W, 200, 500 and 700, and Zyxel's newer platforms genuinely do use per-unit label passwords. Either way, first login forces you onto the Update Admin Info screen to change it.

What do the lights on the Zyxel USG Flex 100 mean?

Here is what each light on the Zyxel USG Flex 100 is telling you, and what to do about it.

Light	What it means	What to do
PWRsolid green	The device is turned on.
PWRoff	The device is turned off.	Check the power lead and the socket.
PWRsolid red	A hardware component has failed.	Zyxel's instruction is to shut the device down, wait a few minutes and restart it. If it comes back red, it is a hardware fault and needs the supplier.
SYSsolid green	The device is ready and running.
SYSflashing green	The device is booting.	Wait for it to settle. This is also the light that tells you a factory reset has taken, if you are holding RESET.
SYSoff	The device is not ready, or has failed.	If it stays off well after power-up, treat it as a boot failure rather than a configuration problem.
SYSsolid red	The device has an error or has failed.
2.4Gsolid green	The 2.4GHz wireless interface is ready. Applies to the 100W and 100AX only — the plain FLEX 100 has no radio.
2.4Gflashing green	The 2.4GHz wireless connection is active. 100W and 100AX only.
5Gsolid green	The 5GHz wireless interface is ready. 100W and 100AX only.
5Gflashing green	The 5GHz wireless connection is active. 100W and 100AX only.
P1 SFP LINKsolid yellow	The SFP port has a 1000 Mbps link.
P1 SFP LINKsolid green	The SFP port has a 100 Mbps link.
P1 SFP LINKoff	No connection on the SFP port.	Check the module is seated. Note that units at hardware revision 2.0 may not support SFP at all — Zyxel tells you to check the device label.
P1 SFP ACTflashing green	The device is sending or receiving packets on the SFP port.
Port LINK (yellow)solid yellow	That port has a 1000 Mbps link.
Port LINK (yellow)flashing yellow	Sending or receiving packets at 1000 Mbps.
Port LINK (green)solid green	That port has a 10 or 100 Mbps link.	If you expected gigabit, check the patch lead and the far end.
Port LINK (green)flashing green	Sending or receiving packets at 10 or 100 Mbps.
Port LINKoff	No connection on that port.	Reseat both ends of the cable, then try a known-good lead.

How do you reset a Zyxel USG Flex 100?

What you lose. The reset overwrites startup-config.conf with the system defaults, which clears all security policies, NAT rules, IPsec and SSL VPN configuration and pre-shared keys, VLANs and interface addressing, zones, address and service objects, user accounts and directory integration, content filtering and anti-malware policy, and the controller configuration for any Zyxel access points the unit manages. The LAN goes back to 192.168.1.1 and the password to 1234. One genuinely softer detail than most firewalls in this class: Zyxel states that "any configuration files or shell scripts that you saved on the Zyxel Device should still be available afterwards", so a saved .conf file on the box survives and can be re-applied.

There is a RESET button on the front panel. Zyxel documents it as: "Press the button in for about 5 seconds (or until the SYS LED starts to blink), then release it to return the Zyxel Device to the factory defaults." The Troubleshooting chapter gives the fuller version — make sure the SYS light is on and not blinking, hold RESET until it starts to blink, then release and wait for the restart.
Hold it for About 5 seconds, or until the SYS light starts to blink. The light is the real signal; the 5 seconds is Zyxel's approximation..
Release, and give the unit a few minutes to restart before trying to connect.

Because saved configuration files survive, a site that kept a named config on the unit can reset and reload rather than rebuild. That is worth doing deliberately before you need it.

A reboot is not a reset. A power cycle or a restart from the web interface keeps every setting. Only RESET clears them.

What if you cannot get into the Zyxel USG Flex 100 at all?

A lost password cannot be recovered on this model. There is no backdoor, no master password and no way for the manufacturer to retrieve it.

There is no dedicated password recovery route. Zyxel's documented answer to a forgotten password is the reset button: "if you still cannot access the Zyxel Device by any method or you forget the administrator password(s), you can reset the Zyxel Device to its factory-default settings". There is a console port and a full CLI, but Zyxel documents no console password reset for this platform. The partial mitigation is the saved-configuration behaviour above — reset, log back in with 1234, and reload the config file you left on the box.

That leaves two options, in this order: find whoever set the unit up and ask them, or factory reset it and rebuild the configuration from scratch. Restoring a configuration backup does not help, because the backup contains the same password you do not know.

Worth knowing about the Zyxel USG Flex 100

Zyxel changed its own documented default between guide editions. The 2020 guide says the password is 1234, full stop; the 2026 guide's front matter says "See Zyxel Device label or 1234" while its body still says 1234. Try 1234, then check the label.
The unit can be adopted into Zyxel Nebula Control Center. Once it has been, the login address becomes whatever NCC assigned and local administration changes character, so a promise of 192.168.1.1 will be wrong for that unit.
There is a hardware revision split: units at HW Rev 2.0 may not support SFP. Two USG FLEX 100s with the same model number can therefore have different port capability, and Zyxel tells you to check the device label to find out which you have.
Password complexity enforcement is not switched on by default, so after the forced first change 1234 can legitimately be replaced with another weak password. Turn the setting on if you care.
myrouter.local works on current firmware as an alternative to the IP address, and is not mentioned in the older guide at all.
The console runs at 115200 baud — different again from the Sophos at 38,400 and the FortiGate at 9600.
The security services — IPS, anti-malware, content filtering, reputation filter and sandboxing — are licensed with a one-year bundled validity. The firewall keeps routing when they lapse; it just stops inspecting.

Where this comes from

Zyxel USG FLEX 100 User's Guide V5.42 — Current guide, January 2026. Source of the address, the reset procedure, the light table and both sides of the password contradiction.
Zyxel USG FLEX 100 User's Guide V4.50 — The 2020 edition, which gives admin / 1234 with no ambiguity.
Zyxel download library — USG FLEX 100 — Evidence the model is still actively maintained: firmware dated August 2026 and a guide dated February 2026.