Russian PPPoE (Dual Access)
See
https://www.gargoyle-router.com/phpbb/viewtopic.php?f=13&t=2219
https://community.ubnt.com/t5/airOS-Software-Configuration/PPPoE-Dual-Access-in-router-mode/td-p/132427
https://forum.openwrt.org/viewtopic.php?id=51241