The PPPoE client will not connect

You have set up PPPoE, the script is pasted, and the client gets no further than dialling. Or it connects for a second and falls out again. No address arrives and there is no default route.

This chapter is about a PPPoE session that never comes up. If it does connect and still nothing goes out, go to No internet after applying. If everything works but some sites load halfway, that is an MTU story: see Websites hang while loading.

The quick checks, in order

1. What is the status? /interface pppoe-client print. A good answer is status: connected. dialing or searching for services... means nobody is answering on the cable; an authentication failure means somebody is answering and rejecting your details. Those are two completely different problems.
2. What does the log say? /log print where topics~"pppoe". It is written out there: authentication failed, no service named ..., or terminating... peer is not responding.
3. Is the underlying interface running? /interface print. Look for the R flag on the WAN port, and with a tagged uplink on the VLAN interface under it as well. Without a link on the port nothing can be dialled.
4. Does the VLAN interface exist? /interface vlan print. A good answer with a tagged uplink is an interface named ether1-vlan6 (or your id) on the right port.
5. What came in? /interface pppoe-client monitor pppoe-out1. A good answer on a connected session has a local-address, a remote-address and an MTU of 1492.
6. Is there a default route? /ip route print. A good answer is an active 0.0.0.0/0 via pppoe-out1.

The usual causes, most common first

The uplink needs a VLAN tag

Many fibre connections deliver PPPoE on a tagged VLAN. Without that tag the router hears nothing and keeps searching for a service. In the Netherlands VLAN 6 is the best known one. This is cause number one for a client stuck on searching for services.

A typo in the username

Almost always the suffix: many ISPs want name@provider and not just name. An authentication failure in the log means the cable and the tag are right and only the credentials are not. The password sits in plain text in your script, so you can compare it line by line.

The cable is in the wrong port

The script dials on the port you picked in the tool. Check with /interface print which port is actually running.

A service name that does not exist

Leave Service name empty unless your ISP prescribes one. Fill in a name the concentrator does not offer and you get no service named while somebody is very much listening.

The modem terminates the session itself

If the modem or ONT is still acting as a router, it is already logged in and there is nothing left for your router to dial. Put it in bridge mode. See Two routers behind each other.

An MTU above 1492

PPPoE takes eight bytes out of the Ethernet frame, so 1492 is the normal maximum on a 1500 port. Fill in more and it only works if your ISP supports RFC 4638. The tool warns about it and raises the port underneath to the MTU plus eight; if your ISP does not support it, leave the field empty.

The line is not provisioned yet

A new connection that has not been switched over, or a line still tied to the old modem's MAC address. Two PPPoE clients on the same line also push each other off in turns.

What the configurator does about it

In the WAN and internet section you set an uplink's type to PPPoE. That brings up the fields that matter: username, password, PPPoE interface name, service name, VLAN id on the WAN port, MTU, route distance, gateway check, use ISP DNS and add default route.

With a VLAN id the script first creates an /interface vlan named <port>-vlan<id> and puts the PPPoE client on top of it. The PPPoE interface itself, so pppoe-out1 rather than the port, then goes into the WAN interface list. That is exactly the link the masquerade rule matches on; with the port there instead, nothing would go out while the session is perfectly connected.

The Clamp TCP MSS toggle is on as soon as there is a PPPoE uplink. Switch it off and the tool warns that websites will hang while loading. Under Provider presets the right combination of type, VLAN tag and DNS is ready per provider.

Not checked: whether your username and password are right, whether your ISP wants PPPoE or DHCP, and which VLAN id your line uses. Only your ISP knows that. The tool also does not look for an existing PPPoE server on your line, and cannot see whether your modem is bridged.

When it is not your router

Check on the modem or ONT whether the connection light is on before you keep digging in RouterOS. Ask your ISP which VLAN id and which service name the line uses, and whether the username needs a suffix. A line tied to the old modem's MAC often lets go after the modem has been off for a quarter of an hour.

Read on: WAN and internet, KPN and MTU.