Re: [lwip-users] How do I control the numbers of TCP connection to the same port?

[address@hidden]

Bill Auerbach wrote:
> This means tcp_listen_with_backlog can be used to enforce only one
> connection?
Exactly. That's what the backlog parameter in posix listen() does, also.

> If this backlog limit is exceeded, what happens?
>    
Incoming connections will be sent a RST. However, this doesn't limit
concurrent connections by default: it has been introduced to limit the
outstanding-connection-queue for netconn- or socket-API. Normally, for
the raw API, there is no such thing (that lies in the nature of the
single-threaded callback mechanism). However, when using this feature,
you have to call tcp_accepted from your appect function to decrease this
counter. If you defer calling tcp_accepted and call it later, you can
implement a concurrent-connection limitation.

When using the socket- or netconn-API, the stack does this for you.
Suppose you have one thread calling accept/recv/send/close in a loop and
set the backlog to 1 then you will only have one active and one pending
connection at a time and all other SYNs coming in will be RST'ed.

Simon