How to enable IPv6 on the China Telecom optical modem? Even when the router switch is turned on, the device still has no address—it's 90% stuck on the optical modem layer

did something foolish last month: I turned on the IPv6 switch in the router's backend, saved it, then excitedly tested it on my phone, and test-ipv6.com gave it a zero. Even though the switch is open, the device still can't get the address. It took me until midnight to figure out one thing—the switch was on the router, and the key was in the optical modem. This article will cover how to enable IPv6 at the telecom optical modem layer, the pitfalls I encountered, and how to verify it all in one go.

take a minute first to figure out which floor your home is stuck on

Don't just go straight into the backstage and mess around. IPv6 has long links—broadband, optical modem, router, device—if any link is disconnected, the result is "no address." My method is rustic but effective, tested in three steps:

Step

: Turn off WiFi on your phone and use data to turn on test-ipv6.com. This isn't testing your own home, it's testing whether telecom currently offers V6. Nowadays, newly installed telecom broadband is basically provided by default. Old plans from ten years ago might not exist, so you have to call number 10,000 first to ask. I tested it, 10 points, which means the broadband side is fine.

Step two: find a network cable and plug the computer directly into the optical modem's LAN port (port 1), then test again. If it works, it means the optical modem layer is good; If it doesn't work, the problem is locked in the optical modem. The third step is when it's time to connect to the router for testing.

By the way, before testing, make sure your family is dialing up. I don't know how to judge it, but just look at the I wrote about the difference between optical modems and routers in article. Just look at the router's WAN port IP and you'll get a clear. This directly determines which path you take next.

optical modem is in bridge mode: the modem doesn't need to move, just turn it on the router

If your optical modem has already switched to bridging and the router handles PPPoE dialing, congratulations—you don't need to change any configuration lines on the optical modem. IPv6 addresses and prefixes are negotiated during dial-up. When the router initiates a PPP connection, IPv6CP shakes hands, the operator hands over both the address and prefix.

All you need to do is turn on V6 on the router. Mercury's network parameters are in advanced settings, Xiaomi's is all the way to the internet settings, and Tenda's WAN method is carefully selected—I wrote the full pitfalls for these three brands in Mercury IPv6 , Xiaomi IPv6 , and Tenda IPv6 here. In bridge mode, 99% of the issues are on the router side; the optical modem really doesn't take the blame.

optical modem is routing mode: the backend changes the IP mode to IPv4 and IPv6

most households are like this: the installer assums the optical modem for dial-up, and the router is left as an AP. At this point, the internet connection on the modem only runs IPv4 by default, so you have to manually switch to dual-stack.

browser, most browsers enter the optical modem backend, and most Telecom settings are 192.168.1.1 or 192.168.2.1. Go to "Network" → "Network Settings" (some models call it Broadband Settings), and in the row of connection names, find the one labeled INTERNET_R. R stands for Route Mode. Select it, change the "IP mode" from IPv4 Only to "IPv4 & IPv6," and save.

Then go to 'User Management' → 'IPv6 Settings' and check DHCPv6 Server to enable it. This step is to have the optical modem send the v6 address downward; if you don't check it, the optical modem won't send it down even if it opens automatically.

here's a real-world issue: the ordinary useradmin account is visible and unchangeable on the Huawei HS8145V5 and ZTE F7015T I've seen—the IP mode bar is grayed out. To activate it, you need a telecomadmin super administrator account. I wrote the method in the of the super password. Be mentally prepared for modifying the super admin parameters: some provincial ITMS will push your changes back at midnight. I've written a separate article about what to do if pushed back. You can find it ITMS pushed back. Fortunately, IPv6 options are generally not on the priority list, and I haven't been rejected for over two months after changing them.

after the modification, restart the optical modem and wait two or three minutes before testing.

the most hidden pitfall: the router has an address, but the underlying device has nothing

This is the section I most want to write about in this whole article, because I've been stuck here the longest. Particularly frustrating symptom: When I entered the router's backend, the WAN port clearly showed an IPv6 address starting with 240e, but when the phone and computer connected and checked the ipconfig, the IPv6 address either didn't exist or only had an internal link starting with fe80. test-ipv6.com still 0 points.

root problem is 'prefix delegation.' Huawei's official documentation has a page specifically investigating this issue, showing that quite a few people have fallen into this trap. I'll try to put it plainly: IPv6 doesn't use the same NAT as IPv4—a public address shared by all devices in the house. It requires each device to have its own global address. Where does that address come from? The operator assigns a segment of address (called a prefix like /60 or /56) to your home, the optical modem cuts a segment for use, and the rest is distributed downward to the router, which in turn is distributed to the phone or computer.

problem lies in the "downward division" step. In the optical modem routing modem, many Telecom optical modems only care about their own firmware — they get the prefix from the carrier, use it themselves, and don't assign the prefix to the router that is plugged in. The router's WAN port can use SLAAC to access its own address (so the backend can see the 240e), but since it doesn't have a prefix to split down, it becomes a blank commander, and the device is naturally empty.

three solutions, ranked by their convenience

my top recommendation. Take the Xiaomi router as an example: in the internet settings, just select Passthrough as v6, and your phone will immediately get 240e. The downside is that the router is just a pipe at this layer, the firewall has weaker control over V6, and if you have a NAS at home and want to connect from outside, you have to pay extra attention to security settings.

after the change, how do you confirm it really works

look at three places, choose one:

the most straightforward is test-ipv6.com, which counts as 10 points. On a Windows computer, type ipconfig and find the line for "IPv6 address." The address starting with 240e is the true global address provided by China Telecom; those starting with fe80 don't count—that's the internal network code the device has set up itself. You can also see the IPv6 section in the WiFi details section on your phone. The status page of the optical modem backend also has an IPv6 information section, showing the address and prefix length received on the WAN side.

here's a reminder about the score reading: test-ipv6.com a score of 10 means "you have public network v6," but it does not mean external connections can actively connect. V6 firewalls default to blocking incoming stations, which is correct—don't turn it off blindly. If you really want to use v6 for something useful, like connecting directly to your home NAS without penetration, I've written an article about three remote NAS solutions, v6 is the most cost-effective option among them.

three types don't work, don't blame the light mode

First, device caching. Windows ipconfig /flushdns clears DNS cache, then disconnects and reconnects; Forget about WiFi and reconnect your phone—don't just stand there refreshing.

the second option, which didn't fully reboot. After saving the modem, restart once for two to three minutes; The router's WAN also needs to be reconnected; some routers require a full reboot before re-initiating the v6 request. After making corrections, wait five minutes before making a conclusion.

third, DNS takes a wrong turn. If you get the address but the webpage can't be opened, if you can ping the IP or the domain name doesn't work, that's the DNS issue—in a v6 environment, the DNS server used by the device may still be stuck in the old location. How to check and modify DNS on the optical modem side? I wrote about this in the about changing DNS on the optical modem, so I won't elaborate here.

to set my expectations flat: IPv6 does not increase speed. It solves the problem of "whether each device can have its own unique address number," the download speed remains the same, and game latency won't improve just because V6 is enabled. Its value lies in scenarios like remote direct connections. The article about checking public IPs about the operator's side door number issue is , and V6 is its alternative solution.

wrap up with a sequence: follow it to avoid going far: traffic test broadband→ plug in the computer directly to the optical modem, test modem→ connect to router, check full-link → bridge, check router → change routing mode, change IP mode to DHCPv6→ WAN has addresses, device not to use Passthrough→ don't forget flushdns to add redconnection. In the end, it comes down to one thing: the router's switch is just a name, the modem doesn't add a prefix, and it's all just empty talk.