How to check if you have a public IP for Telecom broadband? You can tell in just three steps that after I call 10,000 and need to return, connecting remotely to NAS is truly stable
Last year, I set up port forwarding according to tutorials to upload photos of my home NAS while I was outside. My phone switched to data but couldn't connect, and the router restarted three times. At one point, I suspected the router was broken. Later, I realized the problem wasn't with the router: my broadband doesn't have a public IP at all, and no matter how standard port forwarding is, it's just useless. This article will explain how to use three steps to determine whether your home has a public IP address, how to get it back, and what pitfalls might be hidden after getting it back.
clarify first: what exactly is a public IP
public IP is a unique address on the internet, allowing others to directly find your home. Home broadband without a public IP receives the operator's internal network address, and the data must first pass through the operator's translator before being forwarded to your home. For example: having a public IP is a private courtyard, with a unique house number in the city, and delivery is delivered directly to your doorstep; Without a public IP address, living in an office building shares one front desk. Outsiders can only call the switchboard, which doesn't recognize you, and packages will never reach your desk.
Why is there basically no newly installed broadband nowadays? IPv4 addresses were allocated years ago. Giving one public IP to one household was too luxurious, so operators developed a technology called CGNAT (carrier-level NAT), allowing hundreds of households to share one or two public IPs without any impact on external internet access—after all, you just browse the web and watch videos. But the reverse connection—when you want to connect to your home while outside—the switchboard doesn't know who to relay.
CGNAT has a very recognizable mark: the IP obtained by the optical modem or router WAN port starts with 100.64 to 100.127. This address is specifically assigned to CGNAT; seeing it can basically be a verdict. The first time I saw 100.68.44.x on the modem modem status page, I was puzzled—what happened to the promised 192.168? After checking, I found out this was the code for sharing the front desk.
three-step self-check, results in two minutes
Step one: Find the WAN port IP of your 'device dialing that device' in your home. For optical modem dialing, connect your phone to the optical modem WiFi, enter 192.168.2.1 in your browser, log in with useradmin, and you can see the IP address on the status page or in the network-WAN connection. Huawei HS8145V5 is already on the first screen of the "Status" page. On the ZTE F7015T, click the internet connection in the "Network" menu to check. If you have changed the bridge or router dial-up yourself, then check the router's page: go to the router management page (usually 192.168.1.1), and the IP in the internet settings or WAN port status is the same. If you have both an optical modem and router at home, remember that only the direct dial-in WAN port IP of the unit counts.
Step two, check your export IP. Turn off your phone's WiFi, use data to access the internet, search for "IP" in your browser, or visit websites like IP138, where the page will give you an IP address. This step must be checked with data data—connecting to home WiFi only shows the internal network address, which is meaningless.
Step 3: Align the two IPs together.
| see the situation | conclusion |
| WAN port IP and export IP are exactly the same, and not starting with 100.64, 192.168, 10, or 172.16 | Congratulations, you have public internet IP |
| WAN port IP starts with 100.64~100.127 | CGNAT solid proof. Don't struggle |
| the two IPs don't match, and the WAN port looks normal IP | most likely CGNAT, the carrier has given a middle-tier |
my optical modem, WAN port 100.68.44.x, data check outbound 117.136.x.x, but the two characters don't match, solid proof. At that moment, I actually felt relieved—it wasn't that I had read the tutorial wrong, Qidian was gone.
it turns out to be CGNAT, there are two options
first way, call 10,000 and directly get a public IP. This is free, and many people don't know about it. The script is sophisticated: say, "I have storage devices at home and need to remotely access data from the company. Please help me activate a public IP address." Don't just say things like 'I want to run a server' or 'I want to start a website'—such statements are easily rejected on the spot. If customer service says, "They don't provide it now" or "The technology doesn't support it," insist on submitting a work order. Most provinces can issue home broadband. From making the call to redialing the optical modem and obtaining the public IP address, I waited two days, and in the meantime received a follow-up call to confirm the purpose. Some friends in their provinces changed their address on the spot—just one redial of the modem changed the WAN port from 100.68 to the official address starting with 117.
second path: avoid bargaining with carriers and go for IPv6. China Telecom now provides plenty of IPv6 addresses. Optical modem LAN devices can get addresses starting with 240e, and mobile data is basically all IPv6. If both ends are connected, you can connect remotely using IPv6 addresses plus DDNS, without needing public IPv4. I wrote about the specific approach to IPv6 in my about remote connection to home NAS, but I won't elaborate here. The downside is clear: many company and hotel WiFi haven't connected IPv6 yet, so you can connect anywhere you travel. IPv4 public IPs are still more stable.
if you don't even bother making calls, you can use internal network penetration services like FRP or Tailscale, but that's a different approach. The pros and cons were compared in the 763 article, but this article focuses only on the public IP route.
don't get too excited about public IPs—the optical modem is still holding back another layer of
this is the second big pit. By default, the installed optical modem is in routing mode, with the public IP on the modem. Your router has an additional NAT layer below the modem—Dual-layer Translation. If you set port forwarding on the router, packets at the outermost optical modem are blocked and can't enter the router at all. It's just like having no public IP: the forwarding is effective, but you just can't connect.
there are two ways to demolish this floor. To save the hassle, stay in optical modem routing modem, use telecomadmin to enter the optical modem backend for port mapping or DMZ, and point to the router. I've written about the operation details in the of the Super Password. But operations on optical modem are threatened by ITMS configuration pushes, and changes might be pushed back in the middle of the night. Identification and response methods are ITMS in that . My usual recommendation is to keep things straightforward: switch the optical modem to bridge, use the router for PPPoE dial-up, place the public IP directly on the router, and handle all port forwarding on your own router—clean and clean. For port forwarding or DMZ, check this comparison . For personal devices, it's best to stick to single-port forwarding, and for high-end ports, forget about 80 and 443—Jiakuan ports are sealed.
Pitfalls of dynamic IPs: IPs drift, DDNS save the
the public IP you want to bring back is dynamic, not lifelong. Normally, carriers won't touch it. My phone hasn't changed for two months, but the optical modem can be replaced by power cut-off and redialing, or data center cut-and-connect devices. I suffered this loss: after a whole night of partition cutting, the IP changed from 117.136.x.x to 111.72.x.x. I couldn't connect to my home NAS at the office. After checking the router for a long time, I finally remembered to check the IP—it had changed, and the domain still pointed to the old address.
solution is DDNS, dynamic domain names. The router comes with this feature (both ASUS and TP have the management page), NAS systems have it too, Synology is in external access in the control panel, and Feiniu is in the system settings network. Choose a service provider, enter your account, and it will automatically point the domain to the new address when your IP addresses change. There are only two key points to set up: update intervals of five minutes are sufficient; don't set it to flash every minute, as it wastes no use; DDNS runs on regularly running devices, and after the optical modem redials, something must be responsible for reporting the new address. You can use a free domain name; buying a legitimate domain for a few dozen yuan a year is much more worry-free.
who is worth the trouble, and who is the only one to quit
| your situation | I suggest |
| look at NAS photos and files at home when you're out | it's worth it. Calling 10000 is public internet IP |
| PS5. I can't find rooms when playing on Switch online | but the public IP can access NAT2. By the way, I checked the NAT type article |
| I installed surveillance at home and want to watch remotely | same as above Public IPs save money compared to vendor cloud storage |
| FamilyMart is just browsing the internet to watch videos | don't mess around. CGNAT has zero impact on you |
| you really can't make calls, and you're too lazy to switch to bridge__. HTML116__ | the inner mesh penetrates the ceiling, visible 763 |
really want to get started, follow this sequence: first check the IP in three steps to confirm the current status; if not, send a 10,000 work request request. After it takes effect, the optical modem redials to verify that the WAN port IP has changed, then switch to the bridge to remove the NAT layer on the optical modem. Then the router forwards the port to the DDNS configuration, and finally power-off and redial once for full rehearsal—if the IP changes, DDNS will catch up within minutes, and the domain can connect, then the link will truly be connected.
