Sorry if this is rather basic, but I can't find the relevant information. I apologise for any misunderstandings in my question. What is puzzling me is how a router accesses the global internet.

At present, my internet is connected through an integrated router/modem (Technicolor TG579var) so it isn't obvious how it is configured. The ISP is Zen Internet and the actual provision is by OpenReach. I want to move to using a Draytek Vigor 167 as a simple VDSL modem, and a Mikrotik router to interface my systems to the modem.

A traceroute shows simple routing from the private LAN to the LAN gateway, and thence to one of my public IP addresses. But the next step is to the address that the Technicolor reports as the gateway. It is not in the same subnet as my IP addresses, nor even in the same IP space at the top level. How does the router know how to get to it?

Is information acquired by PPPoE? Or does DHCP need to be used on the WAN side? Even though I know what the IP addresses must be as they are fixed.

Clearly the Mikrotik router needs PPPoE client configured with the Zen credentials. But what other configuration is needed to make the WAN side work with the ISP, Zen?

In general terms, right out of the box a RB750 will work with port 1 connected to your ISP - PROVIDED that your ISP is delivering plain old network, AND you are getting an IP via DHCP from them. If you need to set up credentialing (commonly PPPoE) then that has to be set up. It's been years since I needed to do that so I don't remember the details, but it was not hard (and I was doing it on an RG750). Now, both ISPs are just giving me plain Ethernet with public addresses - the fiber ONT and cable modem do whatever credentialing is required. Same thing with IP. If your ISP is expecting you to request an IP address via DHCP, the RB750 is already set up to do that. If you have static IPs, you need to adding that (or those) addresses to the WAN interface on the RB750.
So the first step is to find out from your ISP what they want / provide. The DSL modem most likely is just playing dumb modem so all the smarts need to be in the router. Over the many years that I had DSL, part of the time I got just plain dumb internet and part of the time I had to configure PPPoE. Neither was hard to accomplish in the RB750.

When you configure a PPPoE client (which you have to do when your provider uses PPPoE and your modem is transparent), the settings of the PPPoE client have items "add peer DNS" and "add default route" which are enabled by default.
Through these settings and the PPPoE protocol the router automatically adds the DNS servers and the default route as dynamic items to your configuration.
That is how the MikroTik router knows how to route internet traffic (and how to lookup names).

Thanks pe1chl. I knew someone would have the PPPoE setup info...

Thanks very much for answers to this. I waited to be sure I had the router working before posting again! PPPoE was definitely needed to connect to the ISP.

I don't think both of "add peer DNS" and "add default route" were set by default, but I made sure they were ticked.

Now, although it is working, I'm anxious to sort out my firewall - viewtopic.php?t=193873

I would like to take this a stage further and loose the ONT and connect directly to the incoming fiber. Has anyone any ideas, I am on Zen internet with 1 gig connection. Has anyone any ideas?

Richard

Getting rid of ONT is generally a PITA process and Mikrotik makes it rather even harder due to poor support for FTTH/GPON SFP modules. The reason being that ONT is considered as part of optical network by most infrastructure owners (it allows them to have any kind of visibility and O&M) and they don't embrace having random ONT devices connected. In my country ONT devices are property of infrastructure owners even if services are then provided by other companies (those might give customer a router of some kind which service provider can supervise and that one can be replaced by customer's device).