What do broadband errors 678, 691, and 651 mean? Who cares about understanding error codes? I skipped three trips to the service hall

Last year, my mom's broadband was cut off, and the computer dialed 'error 678.' My uncle insisted the router was broken, so he went to the service center to replace it with a new one, but when he got home, it was still 678. The second visit to the service hall said the account was fine. The third time, the technician came and saw that the corridor splitter tail was loose and just tightened. After three trips, I figured it out: the error code is just a responsibility assignment letter from the carrier. Once you understand it, you'll know whether to fix it yourself, check the wiring, or just call for repair—there's no need to fuss over it.

first distinguish who is reporting errors: numeric codes and text errors are two different camps

many people get confused by error codes because they don't notice one thing: the error is reported differently, so the explanation is different

directly set up a broadband dial-up connection on your computer (Win10 and Win11 still retain this feature, but the "Dial-up" option in the settings) will show numeric codes: 678, 691, 651, etc. This kind of scenario is rare nowadays; usually, you encounter it when the optical modem is modified to a bridge or the computer is directly connected to the optical modem during testing.

more common at home is router dial-up. The router does not report numbers, but text. After logging into the 192.168.1.1 backend, you can see the WAN port lines on the "Internet Settings" or "Network Status" page: "PPPoE authentication failed", "Server unresponsive", "WAN port not connected".

these two sets of explanations are actually one-to-one correspondence, and I will explain them together in the table. First, figure out which camp your home belongs to: optical modem router modem, router auto-dialing, check the router's backend text; For bridge users or computer direct dial testing, check the computer's numeric code.

numeric code for computer dialing: a single meter is where the pot is cleared

the four yards I've stepped on plus one less popular one, I've put them all in the table. Here's a key note: 691 is an account issue, 678 and 651 are wiring issues, 769 is a computer issue, .

678 looks like 651, and I couldn't tell the difference before. Later, I realized there was no need to force a split—both were 'not connected to the cable,' and the troubleshooting process was exactly the same: restart the optical modem, reconnect the network cable, and check the light modem's indicator light. If the optical modem (ONT) LOS red light flashes, it means the wiring is broken. I wrote a comparison table in the article about the indicator light ONT. When LOS flashes red light, you can basically call for repair directly, but you can't fix it yourself.

651 one more exclusive action: right-click "This Computer" on your computer→, → Manage Device Manager → network adapter, find your network card, disable it first, then enable it, and dial it again. This action looks mystical—it saved me twice. It's especially useful when the old machine's network card driver is exhausted.

three types of text errors in the router's backend, each searching in completely different directions

For families dialing

router, focus on these three sentences. Their inspection direction is far from the same; if you look in the wrong direction, all your efforts are in vain.

"PPPoE authentication failure" — this is the router version of the 691, with the account to blame. Three possibilities: wrong password, overdue bills, or an account that was transferred elsewhere. Don't rush to change your password. First, check the latter two options: check if you owe any fees via the mobile service center app; Then think about whether a second device at home is also dialing— a broadband account can only dial once at the same time, two devices kick each other, it means authentication failed. That time, my father-in-law plugged in the old router again, dialing both at once, but neither could get it on. The correct way to connect two routers: In my on the optical modem connecting two routers, I drew the topology: one for dialing, one for AP, but you can't dial both.

"Server Unresponsive" — This is the most confusing one. It looks like the carrier's fault, but the prime suspect is that the carrier has linked your account to the network card's MAC address . The way to judge is straightforward: Previously, dialing directly from a certain computer could access the internet, but after changing routers, it didn't. The router reported server unresponsive, and 80% of the time it was a MAC binding. The solution is in the next section.

"WAN port not connected" or "link disconnected" — the physical layer is not connected, the network cable is not properly plugged in, the wrong port is plugged in, or the optical modem port is broken. First, check if the network cable is plugged into the router's WAN port (the single color, not mixed with the LAN), and whether the other end is plugged into the optical modem gigabit Ethernet port. Which port is the optical modem gigabit? I wrote an article distinguishing Ethernet ports: inserting the wrong port doesn't report errors but the speed drops to 100Mbps, and the disconnected port only reports no connection.

MAC Address Clone: The Remedy for Unresponsive Servers, Four Steps to Fix It

This move saved me twice; it only takes two minutes to operate." In short: the operator links your account to the network card MAC of the first dial-up device. If the router's MAC doesn't match, the router ignores it. Change the router's MAC to match the old computer, and the regional office will accept it.

steps (the old interfaces of Mercury and TP-Link are similar):

• use the computer that originally could directly dial the internet (wired) to the router's LAN port. 192.168.1.1
• login, find "Network Parameters" → "MAC Address Clone." Some new interfaces are placed in "Advanced Settings" → "Network Parameters" and
• click "" Clone MAC address" button. The line above will become the MAC
• save for the current computer's network card, the router will automatically restart, and then check the WAN port status

two points to note. First, you must use the original computer to log in to the background and clone the router. The router clones the MAC of the currently connected computer, but using another computer to log in is still wrong. Second, the original computer was long discarded, so there's no need to get it back. Just call the carrier and ask customer service to unbind your account's MAC, and that can solve the problem too—you'll just have to wait in line.

by the way, if changing your MAC still doesn't work, check the router's system logs. It records the specific reasons for each failed dial-up, which is much more detailed than a single sentence in the status bar. how to read router logs I wrote an article about it; just follow it.

Three wrongful cases in

691: Don't rush to change your password

changing the password repeatedly upon seeing "authentication failed" is the most common detour. My mom did it before, changed the password three times, and finally found out it was 15 yuan owed. Arrange in this order:

First check arrears . Log in to the mobile service hall app and bind your broadband account. You can see the status on the homepage. If the phone is suspended for overdue fees, it means authentication failed, but payment will resume within ten minutes.

second, check if account has been taken over by someone else. Besides the second device at home being kicked around, there's another situation: the installer comes to the neighbor's home to debug it, tries your account, and forgets to log it out. This kind of call just needs to report the owner's ID and have customer service kick out the online conversation.

third is the of the password itself. How to recover your forgot account password? I've written five ways to recover your broadband account and password Trying it out: check your account in the backend, reinstall your phone work order, check via the service app, call customer service to reset everything. If you really want to enter the password by hand, pay attention to two character pitfalls: lowercase l and number 1, uppercase O and digit 0. There are a lot of them in broadband passwords. I've seen people reset the password and never dial it, only to find out they misread 0 as O. The complete process for reconfiguring the dialing after reset is the article on redialing after resetting. Entering the wrong account password is the biggest pitfall here.