You can use, e.g., wirehsark to see the packet, and it'll label all the data for you. So everything but the remote port will be the same, but that's fine-only one of the four has to differ. If one remote machine makes multiple connections, each one will use a different remote port. all connections to sshd will be on local-ip:22). These values should not be the same, and likely are causing one of the Connectors to fail to start. Typically, the local port and local IP will be the same for all connections to a server process (e.g. You can have multiple connections/sockets, as long as at least one of those differs. If it gets an ACK back, the listen call returns a new socket, set up for that connection.Ī TCP socket is uniquely identified by the four values (remote IP, local IP, remote port, local port). When the kernel receives a SYN packet (the start of a TCP connection) with a remote IP of 10.11.12.13 (in the IP header) and a remote port of 12345 (in the TCP header), it then knows the remote IP and port. Then there is a TCP header (with source and destination port, plus more). Like a lot of programs that need to act as a server accepting incoming connections, the Soulseek client first tries talking to your router via UPnP and/or NAT-PMP in order to get the router to configure the port forwarding automatically In SoulseekQt, check your UPnP and NAT-PMP toggles under Options > Login. This is similar to how it finds out the client's IP address (which is part of the IP header).Į.g., every TCP packet includes an IP header (with source IP, destination IP, and protocol, at least). So the server finds out because the client tells it. It's part of the TCP (or UDP, etc.) header, in the packet. Given all that, how does the server find out what port the client is receiving on? I know the client will send TCP segments with a source port and destination port, so the server will use the source port of that segment as its destination port, but what function does the server call to find out about that port? Is it accept()? Firefox is listening at localhost address (listed under Remote host. As soon as the server accepts the client request, the kernel allocates a random port number for the server for further send() and receive(), since the same port number on the server can't be used for sending as well as listening, and the previous port is still listening for new connections remote port 25, and Outbound direction of traffic.
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