PPPoE protocol principle of industrial routers

As we all know, the PPPoE protocol of industrial routers is a common dial-up Internet access method. So what is its principle?

PPPoE: DNS protocol

The Internet is essentially just a very large computer network, and in many ways is not unlike a local area network (LAN). But there are some important differences. Global networks also require their own technology due to the size and capabilities of internet providers and their servers. This technology comes in the form of what’s called Point-to-Point Protocol over Ethernet (PPPoE). What does this agreement do?

Why is point-to-point protocol over Ethernet needed?

To establish an Internet connection, the local PC (or other similar end device) must be connected to the Internet through a router. Access is provided by the Internet Service Provider (ISP), which also needs to check whether the client actually has access authorization . Point-to-Point Protocol (PPP) is used to perform this check when the Internet enters a private home via ISDN. During this process, the dial-in media (modem or router) will connect directly to the Internet provider’s node. The provider verifies the data and clears the way to the internet.

For Internet service providers, the advantage of PPP is that the protocol allows them to not only check access authorization, but also determine the amount of data transferred and the time of dial-in. Providers have benefited from the agreement since that time, when it was normal to pay a small fee for network usage. With the rise of DSL and the fact that more than one device per household started using the internet at the same time, a new technology became necessary.

The PPPoE protocol offers the same advantages as PPP, but it allows the technology to run over Ethernet. At the same time, this network technology is the standard everywhere, enabling complex and fast connections. The familiar PPP portion of the data packet is integrated into the Ethernet frame.

How PPP over Ethernet works

PPPoE is part of the TCP/IP protocol stack – at the lowest level: network access. The network works in two different stages, which in turn affects the setup. It starts with PPPoE discovery. In this step, the protocol determines the node’s MAC address in order to use it to access the Internet. The search is performed via broadcast: packets are sent to the network with no specific destination. The node, also known as a point of presence (PoP), then responds and creates a communication layer between the two network participants.

Next, the second phase begins: the PPPoE session. Negotiate details at this stage. For example, the node checks the client’s access authorization. Actual Internet use follows – but this is still part of the PPPoE session phase.

You can determine which phase is active through the Type field of the Ethernet frame. Here you can find 0x8863 for discovery or 0x8864 for session. The type field is followed by the PPPoE frame, which is embedded in the data field of the Ethernet frame. PPPoE sections can also be assigned to different sections. First, send the PPPoE version. However, since there is only one version of the protocol, the value 1 is always specified here. Next is the PPPoE type, also always represented by 1.

Although the first two parts only take up 4 bits each, they are followed by a 1-byte (ie 8-bit) code field. This is very important for the PPPoE discovery phase and shows which step both communication participants are in. If you are already in the session phase, this field only contains the value 0x00. However, there are five different values ​​possible during the discovery phase:

● 0x09: PPPoE Active Discovery Initiation (PADI)

● 0x07: PPPoE Active Discovery Discount (PADO)

● 0x19: PPPoE active discovery request (PADR)

● 0x65: PPPoE Activity Discovery Session Acknowledgment (PADS)

● 0xa7: PPPoE Active Discovery Terminal (PADT)

Therefore, the discovery phase starts with a broadcast (PADI). During this step, the client also sends its MAC address so that it can then receive a response. The following packet from the PoP contains its own MAC address and name (PADO). Multiple nodes are likely to respond to the client’s broadcast. Then, based on the name, the local computer or router must determine which PoP it wishes to connect to. It communicates this decision to the relevant nodes via another message (PADR). The PoP then contacts the network participant again, confirms the connection, and assigns the device a session ID (PADS). The client then connects to the Internet. If one of the participants wishes to terminate the connection, it is transmitted to the other device along with the final data packet (PADT).

After the connection is established and the session ID has been emitted by the point of presence, other fields in the frame come into play. First, enter your session ID here. This allows all subsequent packets to be identified. Next, indicate the length of the final payload field. This ensures that no information is lost during transmission. The following protocol field provides information about which protocol the payload uses (such as IPv4 or IPv6). Each of these three fields is two bytes long. This payload field finally contains the actual data for transmission. The length of this part can vary (although it is communicated in advance) and the conclusion of the PPPoE frame can be drawn.

Advantages of PPPoE

Point-to-point over Ethernet is closely related to the development of DSL and the general popularity of the Internet. The previous protocol, PPP, was designed for dial-up lines such as ISDN. Ethernet standards are also established over DSL. As a As a result, old protocols that were previously successful had to be adapted. Additionally, Ethernet enables multiple devices to share the same connection to access the Internet. Traditional peer-to-peer protocols cannot do this either.

In most cases, the router is responsible for contacting the Internet provider directly and therefore establishing the Internet connection. However, using PPPoE, a single device can also communicate with the PoP. To do this, PPPoE passthrough needs to be activated in the router. The router will then directly

Mots-clés : Routeur 4G industriel