On my system I have multiple IP addressed. A UDP socket is listening to them all by binding to 0.0.0.0:5005.
Call recvfrom to wait for data.
In the response a sockaddr is filled with the address of the remote sender.
But how do I get to know which of my local IP the packet was sent to?
Is the a way to know?
Or do I need to explicitly open a socket for each IP address on the system?
Related
Lets assume Host X has a UDP Socket running on Port 1337.
Now Host Y and Z both send a UDP Packet to port 1337 of Host X.
Are the packets going to be de-muxed?
UDP is a transfer protocol with no guarantees of delivery and doesn't have much of an implementation.
When both host Y an Z send a UDP packet to port 1337, and assuming both packets arrive, the application listening on port 1337 decides what happens with those packages. The application can choose which packet to demux, to demux both or to demux neither.
Hope this clears things up
I am trying to monitor a remote IP port for outgoing data.
At the minute I have a TCP port connected which is stuck in a deliberate (almost) infinite loop.
This works, until the tcp connection is broken for any reason.
It just feels better to monitor the remote port for outgoing data, but all the classes/functions I find are for receiving data on a particular port.
Any ideas?
I'm working on a project to determine from my Apache logs the geographic location of incoming requests.
My question in this context is, which IP address does Apache log - the HTTP request header IP address or the connecting device's IP address acquired from the incoming socket connection?
It's from the socket (TCP/IP layer) connection, not HTTP.
(There's no remote-address HTTP header.)
I have an application that uses sendto() with UDP to check resources on different ports. How can I get the ICMP port unreachable packet using recvfrom()?
My recvfrom() is like this:
SOCKADDR_STORAGE saFrom;
int nFromLen = sizeof( SOCKADDR_STORAGE );
nReceived = recvfrom ( Socket, Buffer, BufferSize, 0, ( struct sockaddr * ) &saFrom, (socklen_t *)&nFromLen );
When an ICMP port unreachable occurs, nReceived = -1, and WSAGetLastError() returns WSAECONNRESET(10054).
But since I'm checking on different ports, I'd like a way of determining which port triggered the ICMP port unreachable message. How can I determine that? (Maybe I can set some socket options?)
Edit:
As per Len's suggestion(use ICMP only), I tried to create a socket by socket (AF_INET, SOCK_RAW, IPPROTO_ICMP), then call recvfrom() on it. recvfrom() returns 10022(WSAEINVAL) error because the socket is not bound. How should I fix that?
You can't, see my blog posting on the subject here: http://www.lenholgate.com/blog/2007/12/bug-in-overlapped-udp-port-unreachable-errors.html
If you're on XP, then you can use SIO_UDP_CONNRESET with WSAIoctl to control if you get ERROR_PORT_UNREACHABLE reported rather than WSAECONNRESET but even with that set (or on an OS where this is the default) you still do not get the address of the remote port where the ICMP port unreachable happened.
I suggest you use one socket per port you're checking, that way you'll be able to determine where the error came from. Or use ICMP directly.
I have a system that is running on windows.
I have in that system a process that waits for another process on the same machine for a udp message. The message itself is not important (garbage), but the important thing is that I got the event of the message itself.
The problem is that it seems that I get from another local program a UDP message and I don't know from where. I added information about the sender in the recieved UDP message. I see that I get message from valid local port but also from the addres 0.0.0.0 .
I can't understand the 0.0.0.0 . Does anyone has an idea ?
A computer without an assigned IP address could send such packet, even across the network - see e.g. a similar mechanism in DHCP, where the DHCP discovery packet is sent with source address of 0.0.0.0
On a local computer, could this be that the packet is sent (and received) on an interface that is up but without an IP address?
Also, this can mean "broadcast" - if this article on e2 is correct, it is a deprecated method of making a broadcast packet, but apparently it was never removed.
Because it is a udp message and using async type, when reading messages that arrive from the other program I can't know when stop reading, when I get reading the message and I get 0.0.0.0 it means I read everything from the UDP buffer from OS.