Unix Sockets : AF_LOCAL vs AF_INET

Question

I'm just starting with socket programming in UNIX and I was reading the man pages for the socket system call. I'm a bit confused about the AF_LOCAL argument and when it is used. The manual just says local communication. Wouldn't an AF_INET format also work for local communication?

Answer 1

AF_LOCAL uses UNIX domain sockets which are local to the filesystem and can be used for internal communications. AF_INET is an IP socket. AF_LOCAL will not incur some performance penalties related to sending data over IP. See this old but very nice discussion of the topic.