What is PPPoE

PPPoE (PPP over Ethernet) is a protocol for using PPP functions via Ethernet.

 PPP was originally developed for connecting to a network by dial-up or ISDN, and PPPoE enables PPP to be used in environments where ADSL and FTTH services are always connected.

 PPPoE, unlike PPP, identifies both computers by the unique MAC address burned into the NIC and establishes a virtual circuit between them. Then, PPP packets can be exchanged on that virtual circuit, and the user name and password can be checked.

PPPoE is now the Internet standard protocol for broadband connections.

● PPPoE frame

IP packets are extracted from the MAC frames sent from the PC at the broadband router.

 Then, the extracted IP packet is encapsulated with a PPP header at the beginning, and then encapsulated with a PPPoE header. A PPPoE frame is obtained by encapsulating this again with a MAC frame.

 As you can see from the structure of the PPPoE frame in the above figure, what is included in the PPPoE frame is a PPP frame.

 After receiving the PPPoE frame, the access server on the provider side extracts the PPP frame from the PPPoE frame, making it possible to communicate using PPP.

PPPoE (MTU issue)

The flow for browsing the homepage is as follows.

・The web browser establishes a TCP connection with the web server based on the entered URL.
・In that connection, set "MTU-40" in the TCP option of the SYN packet and send it to the Web server as the maximum length of data that you can connect to.
・The web server creates and sends an IP packet based on the notified