These attributes may be used to describe the sender of a network exchange/packet. These should be used when there is no client/server relationship between the two sides, or when that relationship is unknown. This covers low-level network interactions (e.g. packet tracing) where you don’t know if there was a connection or which side initiated it. This also covers unidirectional UDP flows and peer-to-peer communication where the “user-facing” surface of the protocol / API does not expose a clear notion of client and server.
|Source address - domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. 
|Source port number
: When observed from the destination side, and when communicating through an intermediary,
source.address SHOULD represent the source address behind any intermediaries, for example proxies, if it’s available.