Using PPPoE as "WAN IP Mode" on the Network --> WAN --> settings page /internet/mwan.asp we can successfully set up a PPPoE connection. Making other changes in the UI, Saving and Rebooting can BREAK the PPPoE configuration, effectively resulting in a truck roll to fix things.
Normally configuring PPPoE creates a file named /etc/options.pppoe_eth2.1 with the following contents:
noauth user 'apartment5a' password 'apartment5a-password' hide-password noipdefault nodefaultroute nodetach usepeerdns noresolvset maxfail 0 g902n_rostelcom_pppoe_feature 0 persist holdoff 1 ipcp-accept-remote ipcp-accept-local lcp-echo-failure 10 lcp-echo-interval 5 ktune default-asyncmap nopcomp noaccomp novj nobsdcomp nodeflate plugin /etc_ro/ppp/plugins/rp-pppoe.so eth2.1
Making a change to QoS Badwidth setting at Network--> QoS--> /internet/QoS.asp Saving and Rebooting will result in the creation of a file named /etc/options.pppoe_KeepAlive with the following contents:
noauth user 'apartment5a' password 'eth2.1' hide-password noipdefault nodefaultroute nodetach usepeerdns noresolvset maxfail 0 g902n_rostelcom_pppoe_feature 0 ipcp-accept-remote ipcp-accept-local lcp-echo-failure 10 lcp-echo-interval 5 ktune default-asyncmap nopcomp noaccomp novj nobsdcomp nodeflate plugin /etc_ro/ppp/plugins/rp-pppoe.so KeepAlive