sockaddr_un ??
 

was asked to maintain someone's code.

see sockaddr_un used. Is it very similar, almost identical to sockaddr_in?

can sockaddr_un be used to setup connection between two linux computer on a lan?

struct sockaddr_un is for a UNIX domain socket. They're only for communication between processes on the same system, and they normally exist in the file system. reading and writing them works like a TCP socket.