Router PPPoE Authentication Failed, Wrong Credentials or Account Problem
The message “PPPoE authentication failed” appears in the router's status page when the router tries to sign in to your provider and the provider refuses. On a computer the same failure often shows as error 691, “Access was denied because the user name and/or password was invalid on the domain”. The cause is almost always the account, not the router: wrong credentials, an unpaid bill, or the account already in use somewhere else.
The fix, in order
Read the exact message in the router status page. Open the admin page and look at the WAN or internet status. “PPPoE authentication failed” points at the account. A message about a timeout or no response points at the line instead, see the modem no internet guide for that.
Re-enter the credentials by hand. In the admin page, set the connection type to PPPoE and type the full username and password again, by hand, not by pasting. Check for missing characters, extra spaces, and case: usernames and passwords are case-sensitive, and some providers require a suffix on the username, such as a domain after the @ sign. Check the details on your installation paperwork or your provider's account page.
Check the account status. Using mobile data, check your provider's app or account page for an unpaid bill, a suspension, or a service change. An account suspended for non-payment fails authentication the same way a wrong password does.
Make sure the account is only dialing once. Most broadband accounts allow only one PPPoE session at a time. If the same credentials are set up on the modem and the router, or on the router and a computer, the two sessions kick each other off. Use PPPoE on the router only, and put the modem in bridge mode if it is dialing itself.
Check the cable is in the WAN port. The cable from the modem must go into the router's WAN or Internet port, not a LAN port. If the modem was recently switched to bridge mode, confirm the cable is in the LAN port on the modem that is bound to the bridge.
Ask the provider to confirm or reset the credentials. If the details look right and the account is in good standing, contact your provider through its official support channel and ask them to confirm the username and reset the password. A provider-side password change, or a MAC address binding left over from an old router, can only be fixed by the provider.
Never share your broadband username and password with anyone except through your provider's official support channel, and never enter them on a site that is not your router's own admin page or your provider's official account page.
If it still happens
If the credentials are confirmed correct, the account is in good standing, and the router still fails authentication, the problem may be a MAC address binding from a previous router. Some providers bind the account to the first router that dials in, and a new router needs the old router's MAC address cloned, or the binding released by the provider. Both are fixed through the provider's official support channel.
Common questions
What does PPPoE authentication failed mean? It means the router sent your broadband username and password to the provider and the provider refused them. The usual causes are wrong credentials, an unpaid or suspended account, or the account already being used by another device.
What is error 691? Error 691 is the Windows version of the same failure: “Access was denied because the user name and/or password was invalid on the domain”. It means the same thing as PPPoE authentication failed, the credentials or the account are the problem.
Why did PPPoE fail after I changed routers? The new router may have the credentials typed slightly wrong, or the provider may have bound the account to the old router's MAC address. Re-enter the credentials by hand, and if that fails, ask the provider to release the binding or clone the old router's MAC address.