This post was written by eli on August 6, 2023
Posted Under: Internet


These are my notes while setting up ZTE’s ONT for GPON on a Linux desktop computer. I bought this thing from AliExpress at 20 USD, and got a cartoon box with the ONT itself, a power supply and a LAN cable.

This is a follow-up from a previous post of mine. I originally got a Nokia ONT when the fiber was installed, but I wanted an ONT that I can talk with. In particular, one that gives some info about the fiber link. Just in case something happens.

The cable of the 12V/0.5A power supply was too short for me, so I remained with the previous one (from Nokia’s ONT).

The software version of the ONT is V6.0.1P1T12 out of the box, which is certified by Bezeq. Couldn’t be better.

By default, this ONT acts as a GPON to Ethernet bridge. However, judging by its menus on the browser interface, it can also act as a router with one Ethernet port: If so requested, it apparently takes care of the PPPoE connection by itself, and is capable of supplying the whole package that comes with a router: NAT, a firewall, a DHCP server, a DNS and whatnot. I didn’t try any of this, so I don’t know how well it works. But it’s worth to keep these possibilities in mind.

In order to reset the ONT’s settings to the default values, press the RESET button with a needle for at least five seconds while the device is on (according to the user manual, didn’t try this).

So how come this thing isn’t sold at ten times the price, rebranded by some big shot company? I think the reason is this:

The PON LED is horribly misleading

According to the user guide, the PON LED is off when the registration has failed, blinking when registration is ongoing, and steadily on when registration is successful.

The problem is that registration doesn’t mean authentication. In other words, the fact that the PON LED is steadily on doesn’t mean that the other side (the OLT) is ready to start a PPPoE session. In particular, if the PON serial number is not set up correctly, the PON LED will be steadily on, even though the fiber link provider has rejected the connection.

Nokia’s modem’s PON led will blink when the serial number is wrong, and it makes sense: The PON is not good to go unless the authentication is successful. I suppose most other ONTs behave this way.

The only way to tell is through the browser interface. More about this below.

Browser interface

The ONT responds to pings and http at port 80 on address A Chinese login screen appears. Switch language by clicking on where is says “English” at the login box’ upper right corner.

The username and password are both “admin” by default.

As already mentioned, this ONT has a lot of features. For me, there were two important ones: The ability to change the PON serial number, so I can replace ONTs without involving my ISP, and the ability to monitor the fiber link’s status and health. This can be crucial when spotting a problem:

Fiber link information on browser interface of ZTE ZXHN F601 GPON ONT

(click to enlarge)

Note that in this screenshot, the GPON State is “Authentication Success”. This is what it should be. If it says “Registration Complete”, it means that the ONT managed through a few stages in the setup process, but the link isn’t up yet: The other side probably rejected the serial number (and/or the password, if such is used). And by the way, when the fiber wasn’t connected at all, it said “Init State”.

Also note the input power, around -27 dBm in my case. It depends on a lot of factors, among others the physical distance to the other fiber transmitter. It can also change if optical splitters are added or removed on the way. All this is normal. But each such change indicates that something has happened on the optical link. So it’s a good way to tell if people are fiddling with the optics, for better and for worse.

These are the changes I made on my box, relative to the default:

  • I turned the firewall off at Security > Firewall (was at “Low”). It’s actually possible to define custom rules, most likely based upon iptables. I don’t think the firewall operates when the ONT functions as a bridge, but just to be sure it won’t mess up.
  • In Security > Service Control, there’s an option for telnet access from WAN. Removed it.
  • In BPDU, disabled BPDU forwarding.

I don’t think any of these changes make any difference when using the ONT as a bridge.

Setting the PON serial number

Note to self: Look for a file named pon-serial-numbers.txt for the previous and new PON serial numbers.

When I first connected the ONT to the fiber, I was surprised to see that the PON LED flashed and then went steady. Say what? The network accepted the ONT’s default serial number without asking any questions?

I then looked at the “PON inform” status page (Status > Network Interface > PON Inform), and it said “Registration Complete”. Wow. That looked really reassuring. However, pppd was less happy with the situation. In fact, it had nobody to talk with:

Aug 06 10:56:21 pppd[36167]: Plugin loaded.
Aug 06 10:56:21 pppd[36167]: RP-PPPoE plugin version 3.8p compiled against pppd 2.4.5
Aug 06 10:56:21 pppd[36168]: pppd 2.4.5 started by root, uid 0
Aug 06 10:56:56 pppd[36168]: Timeout waiting for PADO packets
Aug 06 10:56:56 pppd[36168]: Unable to complete PPPoE Discovery
Aug 06 10:56:56 pppd[36168]: Exit.

Complete silence from the other side. I was being ignored bluntly.

Note that I’m discussing the PPPoE topic in another post of mine.

Solution: I went into the Network > PON > SN menu in the browser interface, and copied the serial number that was printed on my previous ONT in full. It was something like ALCLf8123456. That is, four capital letters, followed by 8 hex digits. There’s also a place to fill in the password. Bezeq’s fiber network apparently doesn’t use a password, so I just wrote “none”. Clicked the “Submit” button, the ONT rebooted (it takes about a minute), and after that the Internet connection was up and running.

And of course, the GPON State appeared as “Authentication Success” in the “POD Inform” page.

So don’t trust the PON LED, and don’t get deceived by the words “Registration Complete”. Unless you feed the serial number that the fiber network provider expects, there’s nobody talking with you.

In fact, there’s an option in browser interface to turn off the LEDs altogether. It seemed like a weird thing to me at first, but maybe this is the Chinese workaround for this issue with the PON LED.

Bottom line

With the Internet link up and running, I ran a speed test. Exactly the same as the Nokia ONT.

So the final verdict is that this a really good ONT, which provides a lot of features and information. The only problem it apparently has is the confusing information regarding the PON link’s status when the serial number is incorrect. Which is probably the reason why this cute thing remains a Chinese no-name product.

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