Is it possible to bind and listen to one IP address with TCP/IP sockets? (Linux/C)

Question

I have always used:

serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);

which means that I will accept connections from any interface. If I replace the INADDR_ANY with “192.168.0.1”. Does this mean I will only accept connections from the IP address of 192.168.0.1, or does it mean I will accept connections from the interface of 192.168.0.1 resides on?

I have a situation now where I have multiple clients (each with a unique IP address but same port number), trying to connect to one server. Can I have multiple listens functions (separate threads) listening to a unique IP address and port? Or do I have to accept any connection and get the network information after I've connected?

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Edit To give more clarification.

If I say serv_addr.sin_addr.s_addr = inet_addr("192.168.0.1") and a client with IP address 192.168.0.2 tries to connect, will the listen command reject this?

Answer 1

The bind address is the local address to listen on; you can specify the address of a local interface.

If you want to control who can connect, you can either inspect the peer address inside the select/accept loop, or limit inbound connections using iptables.

Update

If I say serv_addr.sin_addr.s_addr = inet_addr("192.168.0.1") and a client with IP address 192.168.0.2 tries to connect, will the listen command reject this? I want to be able to have multiple thread, each servicing a unique IP address.

No, the address is an address on a local machine. Given that you're going for a multi-threaded design, I'd recommend you run the listen/accept code in one thread, check the client address, decide what worker thread is appropriate, and then spawn it.

At the risk of showing my age, I still prefer using listen/accept/select for most socket code - it's a personal taste thing, and yes, does influence the design when it comes to blocking/non-blocking IO, buffering, etc.

Answer 2

If I replace the INADDR_ANY with “192.168.0.1”. Does this mean I will only accept connections from the IP address of 192.168.0.1, or does it mean I will accept connections from the interface of 192.168.0.1 resides on?

Yes

I have a situation now where I have multiple clients (each with a unique IP address but same port number), trying to connect to one server. Can I have multiple listens functions (separate threads) listening to a unique IP address and port? Or do I have to accept any connection and get the network information after I've connected?

Yes. You can "fork" (ie create a new thread) for each connection you wish to process, however you'd have to do the filtering yourself. There is no way (that I know off in the API) to offload that work to the stack.