Why not use SO_REUSEADDR on Unix TCP / IP servers?

Question

I have not seen any important TCP / IP server not use SO_REUSEADDR:

• Using Apache SO_REUSEADDR HTTP Server
• Using nginx SO_REUSEADDR
• Very secure use of the FTP protocol SO_REUSEADDR
• exim SO_REUSEADDR use
• Using Postfix SO_REUSEADDR
• Using OpenSSH SO_REUSEADDR

Is there any use case for using SO_REUSEADDR on TCP / IP servers?

I mean, would the OS always use SO_REUSEADDR to crash any server that doesn't use it?

Do you know a TCP / IP server that does not use SO_REUSEADDR for any reason?

(of course, you cannot use it in MSWindows, since it allows you to run two servers on the same port)

Answer 1

Well, UNP (Stevens, 2004) says:

SO_REUSEADDR allows the listening server to start and bind its well-known port, even if there are previously established connections that use this port as its local port.

All TCP servers must specify this socket option in order to allow the server to restart.