In this paper we describe the creation and use of metadata on the early Arpanet as part of normal network function. By using the Arpanet Host‐Host Protocol and its sockets as an entry point for studying the generation of metadata, we show that the development and function of key Arpanet infrastructure can be studied by examining the creation and stabilization of metadata. More specifically, we use the Host‐Host Protocol's sockets as an example of something that, at the level of the network, functions as both network infrastructure and metadata simultaneously. By presenting the function of sockets in tandem with an overview of the Host‐Host Protocol, we argue for the further integrated study of infrastructure and metadata. Finally, we reintroduce the concept of infradata to refer specifically to data that locate data throughout an infrastructure and are required by the infrastructure to function, separating them from established and stabilized standards. We argue for the future application of infradata as a concept for the study of histories and political economies of networks, bridging the largely library and information science (LIS) study of metadata with the largely science and technology studies (STS) domain of infrastructure.