Now for the actual steps: On
Netlink ONU, find out which ethernet port is connected to the
router. In my case, ethernet 1 is connected to the router. Now, do the following... 1. Visit Netlink ONU's admin page (default username: admin, default password: stdONU101 - these may vary upon model and hardware/software version)
2. Visit Network => Internet
3. Choose "Bridge" for "Mode"
4. No need to change Vlan ID (the previous / existing vlan ID would be filled automatically)
5. Service Mode: "Internet"
6. Port Binding: Check "Port 1" and uncheck "Port 2" and uncheck "WLAN". Step 6 is important. If you connected Netlink ONU with the router via ethernet 2, then please check "Port 2" and uncheck the other two. Finally, click "Save/Apply" at the bottom of the page. Visit your router's dashboard and fire-up a new PPPoE client connection. It'd get connected in its first attempt. I hope that helps someone in the future.