How do you modify DNS for Telecom optical modems? Most things can't be changed in useradmin, so I went through all three routes

last month, my home kept spinning when opening the webpage. There was a website that kept jumping to a navigation site. After searching online, everyone said the DNS was messed up by the carrier, so I just changed it to 223.5.5.5. After filling out the network card on my computer, I kept spinning when I needed to, and on the TV, I kept spinning. Later, I typed a line on the command line ipconfig /all and finally understood: the DNS for the whole house in my house is not controlled by the computer itself; it is issued by the optical modem. In this article, I'll go through the whole process of changing DNS on the Telecom optical modem (Tianyi gateway), from 'Who is sending DNS?' to 'Why the change didn't work.' You can skip the pitfalls I've made myself.

Before

get started, take two minutes to see who sent your DNS

changing DNS to the wrong location is the most common wasted effort. On the computer, press Win+R and type cmd and press Enter, type ipconfig/all, scroll down to find the "DNS server" line, and compare with three scenarios:

the first type, it displays 192.168.1.1 or 192.168.2.1—this is the backend address of the optical modem, indicating it operates in routing mode, and all the DNS for all the devices in the house is sent by it. If you only change the DNS of a computer within this structure, other devices won't get any light at all. If you can't tell whether 192.168.2.1 is the optical modem or the router, first check out my teardown comparison .

the second option, it shows the router's address (for example, 192.168.31.1)—meaning the modem has already changed its bridge, the router is dialing, and DNS is managed by the router. In this case, trying to modify the optical modem is completely the opposite.

the third option: if the device is directly connected to the optical modem's WiFi (for example, still connected to the ChinaNet signal), then there's no need to check—the DNS is 100% sent by the optical modem.

here's a detail most people don't know: in optical modem routing mode, the DNS address sent to the device is its own IP, and internally, it forwards these queries to the carrier's DNS, essentially acting as a middleman. So if you see DNS equal to 192.168.1.1, it's not a problem—it's the factory setup of the Tianyi gateway. If you want to understand why DHCP posts these parameters, you can check the I wrote about DHCP.

useradmin into the backend, try out the parts you can fix first

path: enter 192.168.2.1 (some systems use 192.168.1.1), log in with the regular useradmin account with the sticker on the back of the modem. If you can't get in, check this troubleshooting that won't open. After entering, find the "Network" menu and click "LAN Settings." Some models call it "LAN Settings," which has a DHCP configuration page where you can find the input boxes for primary DNS and secondary DNS.

my HS8145V5, the two boxes in useradmin are grayed out, so you can view but not save. This is the norm—many provinces have set LAN write permissions only for superadmin accounts, telecomadmins. So if you're stuck with the changes like me, don't doubt your mistake. Just follow the method the super password post, get it to Telecomadmin and come back to change it. Fill in the two boxes 223.5.5.5 and 119.29.29.29, and save.

Before you start, start by taking photos or copying the original two values in the primary DNS and secondary DNS boxes on paper and then modifying. The DNS addresses issued by carriers vary by province. If the public DNS you enter is even worse (some local banks or video apps recognize local DNS), the original value is your regret medicine—copying it back in two minutes. After saving after modification, the modem will restart once for two to five minutes. Restarting doesn't count as over—DNS is provided to the device under the DHCP lease. If the device doesn't reconnect, it still gets the old configuration. When your phone or computer reconnects to WiFi, it's best to turn off the power on the TV box for half a minute before plugging it in. The DNS cache is more stubborn than you might think.

one more thing: anyone who has altered the internal configuration of the optical modem may be pushed back by ITMS in the middle of the night. It's best to take a screenshot after modification and re-examine it the next morning. I've covered this mechanism thoroughly in the investigation I ITMS in this article.

families connected by optical modems, don't waste your efforts on optical modems

if your home already uses optical modem for bridge and router dialing, congratulations—you don't need to touch the optical modem at all. DNS is sent by the device that dials in, just change the router: see the common paths for all brands DNS the configuration article , and the Xiaomi router in the 31.1 backend Xiaomi version's .

the most awkward part is the middle structure: optical modem router routing modem, with your router and AP mounted below (most common for installation). AP mode doesn't send DHCP, and whole-house DNS is still sent by the optical modem. Changing the router won't take effect even if you say a word. I've drawn the differences between the three connection methods in this article the optical modem connecting two routers. For this kind of family, there are only two options: either use a super controller to switch to the optical modem, or convert the optical modem to a bridge to let the router dial. From now on, DNS and port mapping will all be managed by the router themselves, once and for all. The method of modification is the article on whether bridging is worth it.

changed or just jumped and spun around ads? I stepped into three pitfalls one by one

pit one: device cache. On the computer, the command ipconfig/flushdns cleared again, the phone forgot to reconnect to WiFi, and the TV box lost power. I failed here on my first trip. After modifying the optical modem, I tested for ten minutes with no effect, almost reverted the settings, but after the TV powered off and restarted, it was fine.

pitfall two: IPv6 takes a wrong turn. Currently, telecom broadband defaults to IPv6, but the system prefers IPv6 DNS, which is still sent by the optical modem. You only changed the IPv4 frame, but the v6 lane continues the old path. A quick look test-ipv6.com the V6 is open, which means it's splitting traffic. On Android phones, on the WiFi detail page, you can see the v6 gateway. If the "DNS server" line in the computer's ipconfig/all is followed by an address starting with 240e, it means the v6 DNS is still in the hands of the optical modem. The solution is either to change the v6 DNS on the optical modem's LAN side together (also with an over-moderator), or to point the v6 DNS on the device to Alibaba's 2400:3200::1 setup.

Pitfall 3: Carrier Rush to Answer, This Is the Most Covert. DNS queries go through UDP port 53, which is plaintext. The carrier's device can preemptively return packets on the link—if you clearly enter 223.5.5.5 on your device, the reply might be answered by the carrier on its behalf. Verification command: nslookup whether.114dns.com. This is the domain name officially registered by 114DNS. The returned result shows which DNS the actual response is from—not the one you provided, or it was pre-answered. In this situation, changing the optical modem or router won't solve the problem. The only solution is to encrypt DNS: enable "Use Secure DNS" in your computer browser (available in Edge and Chrome settings), and enter "Private DNS dns.alidns.com" in Android phone settings. Encrypted channel operators can't get a response.

two commands for verification, don't rely on intuition to guess

first cut, nslookup baidu.com, look at the server line at the top. If it shows 223.5.5.5, it means the new DNS has been issued; if it also shows 192.168.1.1, it means the device hasn't received the new configuration. Go back and reconnect to WiFi or clear the cache.

second cut, nslookup whether.114dns.com, specialized for quick answers. The replying party is not your specified DNS, and someone is already answering on your behalf. At this point, stop bothering with optical modems and go straight to encrypted DNS.

there's no command line available on the phone, Android checks the WiFi details to see if there's 'Private DNS', while iOS directly checks the router's background DNS status page. The easiest motion test: Open the site where you used to skip navigation sites, and it's clear at a glance whether it jumps or not. I've also discussed the connection between redirecting to the carrier page and DNS hijacking, in the of the login page redirect.

here's something to be honest about: changing DNS fixes "inoperability, ads appear, and parsing errors," not download speed. This parsing process only takes a few dozen milliseconds. Even with the fastest public DNS, downloading and testing won't increase speed by a single minute. Don't take online claims like "changing DNS doubles your speed." For your internet speed card, first check whether it's due to light degradation, network cables, or bandwidth being stolen—old speed test standards. Don't treat DNS like a cure-all.

wrap up, copy it exactly according to the spot

order is also set up for you: first ipconfig /all figure out who is sending DNS, useradmin enters the optical modem to see if it can be changed, if not, use the super controller or simply change the bridge, reconnect the entire home device, check NSLOOKUP, and if an ad pops up, you're getting a rushed answer. Then use the encrypted DNS on your browser and phone to finish. In the end, here's a simple rule: changing DNS isn't hard; the hard part is getting it right—first figure out where the optical modem stands in your home structure, which works better than any tutorial.