Don't throw away the old optical modem you swapped out: no fiber optic plug, switch to AP as a switch—I'll cover all three pitfalls for you

first think about it: without fiber optic plugging, how much capability do the optical modem have left

Last month, my colleague Xiao Zhou upgraded to Gigabit, and the service center got a free replacement of a 10-Gigabit optical modem HN8145X6. I unplugged the old TEWA-750G and tossed it into the drawer. A few days ago, he tidied up the room and found it, asking me if this thing could be revived, and it would be a shame to throw it away.

can. But first, you need to understand that the optical modem's capabilities are two pieces pieced together: one is photoelectric conversion, which converts optical signals from the fiber into electrical signals in the network cable, which requires the OLT equipment on the other end of the data center to be valid; The other is the local small switch. The network port on the back and its own WiFi antenna are originally bridged into a local area network, which doesn't rely on fiber optics and is plugged in.

So the optical modem without fiber optic mode only loses half of the upper line—dial-up, IPTV, and landline are all useless, and the LOS light keeps flashing red. Don't panic, the red light means "I couldn't find the fiber optic," not because the machine is broken. The complete light message comparison table is this . The local half is doing just fine: exchanges between ports are carried out, WiFi is sent as usual. If you connect the incoming line from the main router to its network port, it becomes a Wi-Fi mute switch.

old rule is to first clarify the ownership: Strictly speaking, a telecom fiber modem is the operator's asset. When you cancel broadband, the technician has to reclaim it. I accompanied my mother-in-law to disassemble the device I was carrying the fiber modem. If you bought an optical modem out of your own pocket, like the second-hand TEWA I got for my old house, or if the technician didn't take the old one with you when replacing the machine, then that's your turn to dispose of. Xiao Zhou's unit was bought out by him at the same time as he built the PC, so he could build it however he wanted.

three things before starting a fight: identifying the mouth, entering the backend, and closing the DHCP

The first step is identifying the mouth. Eight out of ten old optical modems are pitfalls: the whole device has only 1 gigabit Ethernet, the rest are 100Mbps, and the IPTV port is tied to a VLAN, so it can't be used as a regular port. Regarding the law, I wrote thoroughly in the article Gigabit and Hundred-Gigabit : look at the silk screen, GE is Gigabit, FE is Gigabit; The most reliable option is to go to the backend status page and see if each port negotiates for 1000M or 100M. Xiao Zhou's TEWA-750G has a 1GB Ethernet port, 400Mbps port 2 and 400Mbps, and port 3 is IPTV. This determines its quality as a switch: only one leg can run fast.

the second item, go backstage. Browser type 192.168.2.1, username useradmin, password is on the sticker on the back of the optical modem. If the technician changed the password back then or the stickers wore out, don't try it hard. If you reset the SIM card and restore the factory password, the password will return to the sticker version, but the cost is all the specs inside—anyway, I don't plan to register for broadband again. Once the specs are cleared, it's just clean. The full factory reset process is in this article. If you can't get in at all, check if the network is correct and if the address is wrong. Check the order of troubleshooting the that can't be opened.

The third item is the Vital Gate: turn off DHCP. The optical modem comes out of the factory as a router, with DHCP enabled and sending IPs to the down-to-back device. Now you want it to be silent. Go to the backend and find network and LAN settings (some firmware calls LAN settings), turn off the DHCP server, save and restart. This entry point is on the same page as changing the LAN port IP. the about moving the network segment has three model paths to be checked. Why

have to shut it down: There can only be one person at home who posts IPs. If the optical modem's DHCP is left off, the main router is also sending messages, and both units call out together—one device answers first and listens to whom. The behavior is especially confusing—half the device uses the main router's IP and everything works fine, while the other half uses the optical modem's IP. The gateway points to an optical modem with no outlet, and the internet can't be accessed, causing issues that fluctuate. Restart and replace the devices to get infected. I wrote about the pitfall of dual DHCP in the article about connecting two routers via optical modem expanding on the topic: one network can only have one transmitter.

after closing it, do one more thing: change the optical modem's own LAN port IP to one wrong digit on the same network segment, and the main router is 192.168.2.1. Change the optical modem to 192.168.2.2. If you don't change it, after turning off DHCP, its own address will be randomly sent by the main router. In a couple of days, if you want to check WiFi in its backend, you'll have to check the main router's device list one by one. Nail one down, and from then on, 192.168.2.2 will always find it.

for switches: plug the incoming cable into the LAN port, get three free ports

In short: the main router uses one LAN cable to plug into the old optical modem's network port 1 (the gigabit one), and the rest connects to the device. It's the same idea as converting an old router to an AP. The sister article is in the article about router as a switch. The difference is that the router still needs to go into the background to switch to working mode, while the optical modem doesn't even need to switch modes. It doesn't even have this concept to begin with; turning off DHCP is like a hub with an antenna.

Xiao Zhou's study has a dedicated network port on the TV wall, which turns out to be NAS exclusive. Desktops and TV boxes can only squeeze into WiFi. Now that cable is plugged into the old optical modem port 1, one port becomes three, and not a cent was spent.

to say the ugly thing up front: a hundred Mbps port is just a hundred Mbps, actual tests max out around 11MB/s, but the physical limit can't be changed. I want to use it to transfer large files between two gigabit devices, for example, copying a 4K original drive from a desktop to a NAS, and the speed drops directly from 110MB/s to just over 10MB/s. If you really need internal network mutual transmission, honestly buy an eight-port gigabit dumb switch, 80 to 90 yuan. I've written key points for choosing. The value of the old optical modem lies in feeding devices that are sufficient for 100Mbps: TV boxes, printers, and wired gateways for smart homes.

2.4G private network AP: Feeding the camera and sweeping machine

WiFi The modification on that side is simpler. The WiFi settings in the background do three things: change the name from ChinaNet-XXXX to something you can recognize; Change the password to the one unified at home; Turn off dual-band integration, leaving only the 2.4G network; just turn off 5G and avoid messy connections. The positions of dual-band switches differ by model. the article on removing dual-band has a comparison table of three models. By the way, the WiFi signal built on the optical modem is notoriously weak. At the same location, the speed is only about half that of a proper router. I counted in the actual test, so its WiFi is only suitable for heavy work—don't expect to supplement the signal.

the answer to this 2.4G network data card is: IoT private networks. Cameras, robot vacuums, and temperature and humidity meters—all slow devices that only recognize 2.4G—are all fixed to the optical modem's network, and the main router's network is quiet. When configuring the network, just make sure to connect with the new name. If your device keeps failing to connect to the internet, about network failure has a complete checklist. After

Xiao Zhou's family made this change, they had an unexpected discovery: the vacuum and camera used to be connected to the dual-band integration of the main router, often offline. I guess the device roamed to 5G on its own, then dropped back when the signal was poor. After being stuck on the old Optical modem's pure 2.4G, it hasn't dropped for half a month. The device is fixed in those few rooms, with 2.4G coverage and speed sufficient.

three pitfalls. In order of stepping on

pit one, LAN ports are not connected. After the modification, Xiao Zhou noticed something strange: the desktop plugged into Ethernet port 4, the NAS plugged into port 2, both connected to the internet, but the desktop couldn't ping the NAS. After some research, I found that some carriers' custom firmware isolates the LAN port, causing a two-layer gap between ports and only speaking to the uplink, meaning "everyone can access the internet but can't find each other." It doesn't matter about box printers, but the need for mutual access to "desktop access to NAS" is fatal. The testing method is simple: after modification, first use two devices to ping each other. Once the connection works, arrange the work; if not, don't force it—leave the mutual access request to the dumb switch.

pitfall 2: not all optical modems have WiFi. My ZTE F7015TV3 focuses on 2.5G ports and 10Gbps, but it doesn't have a WiFi module at all. This can only be used as a wired switch. Proof: The back doesn't have an antenna seam; if the specs page doesn't mention wireless, then it doesn't have it. Before you start, make sure your unit has an antenna. Don't modify it only after drawing up the plan to find out the machine is dumb.

Pitfall 3, can't find the backend. After turning off DHCP, the optical modem's IP drifts (if you didn't listen to the earlier advice stuck in .2). If you want to enter 192.168.2.1 but can't get in, don't think the machine is broken—go to the main router's device list to find its new address, or simply reset and start over. The machine wasn't broken, just the house number was changed.

Conclusion: In what situations is it worth keeping

electricity bill counted: the optical modem runs around 6W all year, and the annual electricity bill is just over thirty yuan; A 3W dumb switch costs only half that amount. Paying for three speakers for electricity is actually about that 2.4G antenna—if the antenna isn't needed, it's not worth it.

Here's the final note: after the upgrade, first change the WiFi password to a strong password. From now on, this machine won't have fiber optic or ITMS to care about; the configuration will be entirely up to you and you to keep it in your own hands. After modifying, take a photo of the wiring and save it on your phone. After half a year, you forget which cable goes in and out. The photo is more reliable than your memory.