1.7.2.UDP

Node discovery messages are sent as UDP datagrams. The maximum size of any packet is 1280 bytes.

Node discovery messages are sent as UDP datagrams. Since UDP is a lossy transport, packets may be received in any order or not at all. Implementations should not re-send packets if the recipient doesn’t respond.

The maximum size of any packet is 1280 bytes. Implementations should not generate or process packets larger than this size. Most messages are smaller than this limit by definition, the exception being the NODES message. FINDNODE returns up to 16 records, plus other data, and TOPICQUERY may also distribute a significantly long list of ENRs. As per specification the maximum size of an ENR is 300 bytes. A NODES message containing all FINDNODE response records would be at least 4800 bytes, not including additional data such as the header. To stay below the size limit, NODES responses are sent as multiple messages and specify the total number of responses in the message.

The minimum size of any Discovery v5 packet is 63 bytes. Implementations should reject packets smaller than this size.

Since low-latency communication is expected, implementations should place short timeouts on request/response interactions. Good timeout values are 500ms for a single request/response and 1s for the handshake.

When responding to a request, the response should be sent to the UDP envelope address of the request.