By default, MSS is chosen as MTU of the outgoing interface minus the usual size of the TCP and IP headers (40 bytes), which results in 1460 bytes for an Ethernet interface. TCP stacks try to avoid fragmentation, so they use an MSS (Maximum Segment Size). Therefore max PPPoE MRU and MTU values must not be larger than 1492. PPPoE adds another 6 bytes of overhead and the PPP field adds two more bytes, leaving 1492 bytes for IP datagram. Typically, the largest Ethernet frame that can be transmitted without fragmentation is 1500 bytes. PPPoE server sends Echo-Request packets to the client to determine the state of the session, otherwise, the server will not be able to determine that session is terminated in cases when a client terminates session without sending Terminate-Request packet. If any process fails, the LCP negotiation establishment phase is started again. IPCP negotiation stage - where the client is assigned an IP address.When a server sends confirmation and a client receives it, PPP Session is started that consists of the following stages: PPP frames are encapsulated in PPPoE session frames, which have Ethernet frame type 0x8864.
When the discovery stage is completed, both peers know PPPoE Session ID and other peer's Ethernet (MAC) address which together defines the PPPoE session. It can be sent by either server or client.
MikroTik RouterOS PPPoE client to any PPPoE server.PPPoE provides the ability to connect a network of hosts over a simple bridging access device to a remote Access Concentrator. It is advised not to use static IP addresses or DHCP on the same interfaces as PPPoE for obvious security reasons. PPPoE standard is defined in RFC 2516. The PPPoE client and server work over any Layer2 Ethernet level interface on the router, for example, Wireless, Ethernet, EoIP, etc. Generally speaking, PPPoE is used to hand out IP addresses to clients based on authentication by username (and also if required, by workstation) as opposed to workstation only authentication where static IP addresses or DHCP are used. Point to Point over Ethernet (PPPoE) is simply a method of encapsulating PPP packets into Ethernet frames. PPPoE is an extension of the standard Point to Point Protocol (PPP) and it the successor of PPPoA.