CODEWITHSUNDEEP
clinuxsockets
RajSanpui
RajSanpui

Reputation: 12064

Is it always required to bind a socket?

Well, my question may look like a basic stuff, but i am new to network programming side. I wish to know:

1) Is it always required to bind a socket in order to receive message from that? I saw a sniffer code (raw socket) one in which directly it is invoking recvfrom and another piece of code in which it is invoking bind and then a receive.

2) What is the difference between the AF_* and PF_* family? Is the later related to POSIX? Which is the one recommended ?

Upvotes: 13

Views: 13697

Answers (3)

Peter Maida
Peter Maida

Reputation: 11

For a client that only sends data, a bind is not necessary.

For a client that is sending a request to a server, and then receiving a response, a bind is not necessary. The server can use the IP address and port number that the incoming data came from.

For a client that is only receiving data, or is receiving data before it sends out data back to the server, a bind is necessary. How will the server know where to send data to? In this sense the "client" is acting like a "server" that needs a place (bound port) for the data to come to.

Upvotes: 1

Remy Lebeau
Remy Lebeau

Reputation: 595827

I don't know about Linux, but on Windows, if recvfrom() is called on an unbound socket, it will fail with an WSAEINVAL error.

Upvotes: 0

MarkR
MarkR

Reputation: 63538

No, you don't need to bind().

If you're using a TCP or UDP socket where you are planning to either connect() or send a packet to a destination with sendto(), the kernel will automatically bind the socket to a suitable port number when you try to connect or send. This is generally the preferred way. bind()ing client sockets is considered harmful.

The same is also true of AF_UNIX sockets - the client side does not need to bind, and should not do so normally.

Upvotes: 13

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