====== RLPx ======
[[dido:public:ra:xapend:xapend.a_glossary:start| Return to Glossary ]]

**RLPx** is a [[dido:public:ra:xapend:xapend.a_glossary:p:start]] suite and not a single protocol. On the one hand it maintains the [[dido:public:ra:xapend:xapend.a_glossary:p:p2p]] overlay network with the means of a modified version of the [[dido:public:ra:xapend:xapend.a_glossary:k:kademlia]] node discovery protocol (using [[dido:public:ra:xapend:xapend.a_glossary:u:udp]] messages). We could name it **RLPx** **Node Discovery Protocol**.

The first time two [[dido:public:ra:xapend:xapend.a_glossary:p:peer | Peers]] meet each other, they should perform a two-phase handshake (i.e. two different handshakes). In the first handshake, they exchange some [[dido:public:ra:xapend:xapend.a_glossary:c:cryptographic_algorithm | ryptographic]] secrets (the details are explained here (in the **RLPx** specification)) that are used for the subsequent communications between them. The subsequent messages are therefore [[ dido:public:ra:xapend:xapend.a_glossary:e:encryption | encrypted]] and [[dido:public:ra:xapend:xapend.a_glossary:a:authentication | authenticated]].

In the second handshake, they exchange their capabilities, i.e. which **''devp2p''** subprotocols they support (the peers can support multiple protocols). This second handshake could be considered already part of **''devp2p''** wire protocol (the **''Hello''** message). The documentation says that:

  : //the ÐΞVp2p nodes communicate by sending messages using RLPx//

(this time using TCP messages). I list some **''devp2p''** wire subprotocols that are widely used:

  * [[dido:public:ra:xapend:xapend.a_glossary:e:eth]], the Ethereum wire subprotocol used to exchange the information about the blockchain
  * [[dido:public:ra:xapend:xapend.a_glossary:w:whisper]]
  * [[dido:public:ra:xapend:xapend.a_glossary:l:les]] the light Ethereum subprotocol is the protocol designed for the light clients
    ...If you want you can write your own subprotocol https://github.com/ethereum/go-ethereum/wiki/Peer-to-Peer.

Therefore, **RLPx** messages are encrypted and authenticated and on top of them you can communicate with different protocols. We can say that **RLPx** is the transport layer protocol and **''devp2p''** and its subprotocols are the application level protocols.

Source: [[https://stackoverflow.com/questions/49029311/what-is-the-use-of-ethereums-rlpx-and-how-do-they-use-it-in-ethereum-ecosystem ]]


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