PPPoE
RFC 2516 A Method for Transmitting PPP Over Ethernet (PPPoE)
https://www.cresc.co.jp/tech/network/RFC_PPPoE/RFC_PPPoE.htm
https://tex2e.github.io/rfc-translater/html/rfc2516.html
RFC 3817 Layer 2 Tunneling Protocol (L2TP) Active Discovery Relay for PPP over Ethernet (PPPoE)
RFC 5578 PPP over Ethernet (PPPoE) Extensions for Credit Flow and Link Metrics
RFC 4938 → 5578
Ethernet 上でPPPっぽい認証などをする