I am working on an application that will receive RTP packets from another local service over UDP. Early in the protocol, I receive a message with the IP address from which I'll be receiving these RTP packets, but the port number will be given as 0 (zero) ... I'm to open my UDP socket using an ephemeral port. My response to the given message will contain the actual port I've opened so the sender can know where to direct the packets.
My networking library is an implementation of sockets with boost::asio. Where can I find clear information on how to open such a socket without specifying a non-zero port i.e. use an ephemeral port? Searching the boost docs for "ephemeral" doesn't give me networking results.
Of course, I'm open to seeing an actual example, but finding good documentation would also be just fine.
Thanks.
I would question using ephemeral ports like that, but ... - you can bind your UDP socket to port 0, then use local_endpoint() to retrieve actual port assigned by the OS.
Related
I found the function: GetTcpTable in C++. In the header: iphlpapi.h. That gives me the destination IP of TCP packet and I was wondering if there's a function from the same header that would give me the destination IP of UDP packet... I tried the function: GetUdpTable but it gives only the local IP and port. I will be more than happy if that function has also code example in C++ of course. Thank you anyway!
EDIT:
I using pcap.h now and i still don't know how to catch UDP packets and take from them the ip. There is a code that i can use?
GetTcpTable() does not give you the destination IP of TCP packets. It merely gives you a list of currently listening TCP ports and active TCP connections.
GetUdpTable() can give you the list of currently listening UDP ports, where UDP packets can be sent to. There are no connections in UDP.
But, if you want to know the actual destination IP for each UDP packet received, and without having to use a low-level capture library like WinPCap, then you can use the WSARecvMsg() function to receive your UDP packets, rather than using the recvfrom() or even recv() function.
WSARecvMsg() can report metadata about each packet, most notably the IP_PKTINFO (IPv4) and IPV6_PKTINFO (IPv6) control blocks, which specify the destination IP of the packet and the index of the network interface that received the packet.
You need to use WSAIoctl(SIO_GET_EXTENSION_FUNCTION_POINTER) to obtain a pointer to the WSARecvMsg() function (see Why is the WSARecvMsg function implemented as a function pointer and can this pointer be reused? for the reason why), and use setsockopt() to enable the IP_PKTINFO/IPV6_PKTINFO socket option, before you start calling WSARecvMsg() to receive packets.
See Function to retrieve the header destination address from a packet in windows XP for an example.
I have two computers, and I have created a network between them, One is server (Windows Server OS) and the client (Windows 10). Both computer also has connection to internet through wifi. To connect two Systems I am using Ethernet Cable
I like to know if I create a program for client in c++ that send packets using internet socket. Should I also create a listener on server too. And should I use port 80 to send packets and same port on server to listen to arriving packets?
Assuming you decide to use TCP, then:
Should I also create a listener on server too?
If you are using a connection-oriented protocol (such as TCP) then you must have one end listening, because otherwise you have no way to create the TCP connection.
And should I use port 80 to send packets and same port on server to listen to arriving packets?
You should use whatever port number you want, as long as something else isn't using it. The actual number doesn't matter as long as the server and client agree.
Valid port numbers are in the range 1 to 65535.
I'm trying to receive multicast packets from a media server. This is the wireshark capture of an example packet:
(source: memecode.com)
There doesn't seem to be any ports involved, just MAC address for source and destination. Most of the source code examples I've seen bind against a specific port when receiving multicast packets. e.g.
https://publib.boulder.ibm.com/infocenter/iseries/v5r3/index.jsp?topic=%2Frzab6%2Frzab6x2multicast.htm
I would like to be able to receive these packets on both Windows and MaxOSX (C++ apps in both cases, ie Win32 API and Carbon, although the Mac port is more important).
How can I do this?
You just create a UDP socket, bind it to the port, join the multicast group, and call recvfrom().
But the packet you captured doesn't look like a UDP multicast packet. Possibly something between the routers? It doesn't have an IP header let alone a UDP header, which is where the IP and port information is,
I have a server written in cpp. It is listening on 0.0.0.0. Now i want to find the network interface from where the server receives the packet. Is there any way to do that?
Use getsockname() to get the IP-address the socket descriptor receiving the packets is bound to.
Then use getifaddr() to loop over the interfaces available, to find which one matches the IP-address found in the 1st step.
In the case where the source port and destination port of a non-blocking TCP socket are not in agreement(for a p2p application), how does one specify the destination port that the socket will Connect() to?
In case of P2P the clients first connect to torrent to get a list of peers(seeders) and the port number which is open at the peer. The system which wants to download will then connect to the peer using the address and port provided by the tracker.
The peers are not restrictive(generally) and accept connections from any source address or ip
Specifying the destination port of a connection is done in the sockadder-struct that you pass to the connect()-call. Since you don't specify which OS you are working on, in it is difficult to provide a concrete example. However, for both Linux and Windows, you would typically load the sockaddr-struct using getaddrinfo(). A nice Linux-example is provided here, while MS has an example in their official documentation.