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  • does the concept of flow apply to tcp as well as udp?

    - by liv2hak
    I have a very large network trace file which contains both tcp and udp packets.I want to find out the flows in the trace file.For that I have a hash function which takes in source ip address,destination ip address,source port,destination port and protocol.In case of TCP I can understand that the flow means all the packets which have the same 5 parameters same.But what does it mean in case of UDP.how does the concept of flow apply in case of UDP.? I am a novice in packet processing.

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  • How to find an available port?

    - by Roman
    I want to start a server which listen to a port. I can specify port explicitly and it works. But I would like to find a port in an automatic way. In this respect I have two questions. In which range of port numbers should I search for? (I used ports 12345, 12346, and 12347 and it was fine). How can I find out if a given port is not occupied by another software?

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  • Artificially create a connection timeout error

    - by Mark Ingram
    I've had a bug in our software that occurs when I receive a connection timeout. These errors are very rare (usually when my connection gets dropped by our internal network). How can I generate this kind of effect artificially so I can test our software? If it matters the app is written in C++/MFC using CAsyncSocket classes. Edit: I've tried using a non-existant host, and I get the socket error: WSAEINVAL (10022) Invalid argument My next attempt was to use Alexander's suggestion of connecting to a different port, e.g. 81 (on my own server though). That worked great. Exactly the same as a dropped connection (60 second wait, then error). Thank you!

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  • Identify machines behind a router uniquely based on ipaddress

    - by Amith George
    Some background first. I have a .net client agent installed on each of the machines in the lan. They are interacting with my central server [website] also on the same lan. It is important for my website to figure out which of the machines can talk to each other. For example, machines of one subnet cannot directly talk to machines of another subnet without configuring the routers and such. But machines in the same subnet should be able to talk to each other directly. The problem I am facing is when the lan setup is like in Figure 1. Because Comp1, Comp2 and Comp3 are behind a router, they have got the ipaddress 192.168.1.2 till 192.168.1.4. My client agent on these machines report the same ipaddress back to the server. However, machines Comp4, Comp5 also have the same ipaddresses. Thus, as far as my server is concerned, there are 2 machines with the same ipaddress. Not just that, because the subnet mask is 255.255.255.0 for all machines, my server is fooled into thinking that Comp1 can directly talk to Comp5, which is not possible. So, how do I solve this? What do I need to change in my client or in my server, so that I can support this scenario. These two are the only things in my control.

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  • Close TCP connection when owner process is already killed

    - by Otiel
    I have a Windows service that - when it starts - opens some WCF services to listen on the 8000 port. It happens that this service crashes sometimes. When it does, the TCP connection is not released, thus causing my service to throw an exception if I try to start it again: AddressAlreadyInUseException: There is already a listener on IP endpoint 0.0.0.0:8000 Some observations: When running CurrPorts or netstat -ano, I can see that the 8000 port is still in use (in LISTENING state) and is owned by the Process ID XXX that corresponded to my service process ID. But my service has already crashed, and does not appear in the Task Manager anymore. Thus I can't kill the process to free the port! Of course, running taskkill /PID XXX returns: ERROR: The process "XXX" not found. When running CurrPorts or netstat -b, I can see that the process name involved in creating the listening port is System, and not as MyService.exe (whereas it is MyService.exe when my service is running). I tried to use CurrPorts to close the connection, but I always get the following error message: Failed to close one or more TCP connections. Be aware that you must run this tool as admin in order to close TCP connections. (Useless to say, I do run CurrPorts as Administrator...) TCPView is not much help either: the process name associated to the 8000 port is <non-existent>, and doing "End process" or "Close connection" has no effect. I tried to see if there was not a child process associated with the PID XXX using Process Explorer, but no luck here. If I close my service properly (before it crashes), the TCP connection is correctly released. This is normal, as I close the WCF service hosts in the OnStop() event of my service. The only way I found to release the connection is to restart the server (which is not convenient in a production environment as you can guess). Waiting does not help, the TCP connection is never released. How can I close the connection without restarting the Windows server? PS: found some questions extremely similar to mine.

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  • Remote desktop in XP?

    - by vineth
    hi, I have enabled remote desktop in my xp sp3 system, (My problem) if my friend take my system in remote with out my authentication my system is connected to him.but few day before i get authentication message(attached in the below link) but nowadays i am not receiving this dialog box... please provide help to get this authentication dialog box.. Link : http://www.freeimagehosting.net/image.php?f9f04c5e0a.jpg Thanks in advance

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  • About Network Address Translation (NAT)?

    - by Rudi
    Just curious about a particular scenario of NAT. Let's suppose we have 4 computers sharing a global IP address under the NAT. I understand that the NAT box keeps an internal record to know which computer to forward requests to. But let's say on computer #2 I'm trying to download a file. And let's say on computer #1, #3, and #4, I'm just browsing the web normally. When the browser initiates a TCP connection to get that file, how does it know which computer to give it to? I mean like, each of the four computers is using port 80 to browse the web right? How does the NAT's record distinguish which "port 80" belongs to which computer?

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  • TACACS lib for java

    - by guaz
    The only open source TACACS lib I was able to find was Jnetlib http://sourceforge.net/projects/jnetlib But there is not any description about how to use it!! Anyone have used it before?? thanks

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  • Can I close and reopen a socket?

    - by Roman
    I learned an example of usage of sockets. In this example a client sends a request to a server to open a socket and then the server (listening to a specific port) opens a socket and everything is fine, socket is "opened" from both sides (client and server). But it is still not clear to me how flexible is this stuff. For example, is it possible for the client to close an opened (from both ends) socket and to reopen it again (under condition that the server keeps the socket opened). Is it possible for the server to "know" that a socket was closed on the client side? Is it possible for the client to know that a socket was closed on the server side?

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  • GAE and Socket Data

    - by Vinod
    I have a field device which keeps on sending data over to any designated port using sockets. I am planning to use GAE for server-side infrastructure. I read GAE does not support sockets. But i can configure the device to send the data over port 80. so we wrote a genericservlet to capture this data on GAE. But it is not obtaining any values from the client. any suggestions to fix this issue?

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  • List of IP addresses/hostnames from local network in Python

    - by joshhunt
    How can I get a list of the IP addresses or host names from a local network easily in Python? It would be best if it was multi-platform, but it needs to work on Mac OS X first, then others follow. Edit: By local I mean all active addresses within a local network, such as 192.168.xxx.xxx. So, if the IP address of my computer (within the local network) is 192.168.1.1, and I have three other connected computers, I would want it to return the IP addresses 192.168.1.2, 192.168.1.3, 192.168.1.4, and possibly their hostnames.

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  • Other than UDP Broadcast or Multicast, what other methods can I use on a WiFI network to discover co

    - by Gubatron
    I've implemented a simple ping/pong protocol to discover other computers connected to the same WiFI router. This works fine on many routers, but it seems some public routers have UDP traffic blocked or disabled. What other options do I have to discover the computers connected to the router? I was thinking of brute forcing TCP attempts (trying to open connections to all possible IPs on my subnetwork) but this would be very costly and I would have to cycle several times and still not find every machine that's recently connected to the network.

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  • What to do when ServerSocket throws IOException and keeping server running

    - by s5804
    Basically I want to create a rock solid server. while (keepRunning.get()) { try { Socket clientSocket = serverSocket.accept(); ... spawn a new thread to handle the client ... } catch (IOException e) { e.printStackTrace(); // NOW WHAT? } } In the IOException block, what to do? Is the Server socket at fault so it need to be recreated? For example wait a few seconds and then serverSocket = ServerSocketFactory.getDefault().createServerSocket(MY_PORT); However if the server socket is still OK, then it is a pity to close it and kill all previously accepted connections that are still communicating. EDIT: After some answers, here my attempt to deal with the IOException. Would the implementation be guaranteeing keeping the server up and only re-create server socket when only necessary? while (keepRunning.get()) { try { Socket clientSocket = serverSocket.accept(); ... spawn a new thread to handle the client ... bindExceptionCounter = 0; } catch (IOException e) { e.printStackTrace(); recreateServerSocket(); } } private void recreateServerSocket() { while (keepRunning) { try { logger.info("Try to re-create Server Socket"); ServerSocket socket = ServerSocketFactory.getDefault().createServerSocket(RateTableServer.RATE_EVENT_SERVER_PORT); // No exception thrown, then use the new socket. serverSocket = socket; break; } catch (BindException e) { logger.info("BindException indicates that the server socket is still good.", e); bindExceptionCounter++; if (bindExceptionCounter < 5) { break; } } catch (IOException e) { logger.warn("Problem to re-create Server Socket", e); e.printStackTrace(); try { Thread.sleep(30000); } catch (InterruptedException ie) { logger.warn(ie); } } } }

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  • How to collect user opinions about software

    - by alga
    I have written a small .net Windows Forms application. And now I decided to get opinions or comments from users. User will just write something in a input form and click a send button. I want to use the most easiest way. I don't want to host any webservices or another applications for gathering the information. Also I don't have a database. Nothing. I just want to know what people think about the application. How would you do it?

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  • Python and C++ Sockets converting packet data

    - by yeus
    First of all, to clarify my goal: There exist two programs written in C in our laboratory. I am working on a Proxy Server (bidirectional) for them (which will also mainpulate the data). And I want to write that proxy server in Python. It is important to know that I know close to nothing about these two programs, I only know the definition file of the packets. Now: assuming a packet definition in one of the C++ programs reads like this: unsigned char Packet[0x32]; // Packet[Length] int z=0; Packet[0]=0x00; // Spare Packet[1]=0x32; // Length Packet[2]=0x01; // Source Packet[3]=0x02; // Destination Packet[4]=0x01; // ID Packet[5]=0x00; // Spare for(z=0;z<=24;z+=8) { Packet[9-z/8]=((int)(720000+armcontrolpacket->dof0_rot*1000)/(int)pow((double)2,(double)z)); Packet[13-z/8]=((int)(720000+armcontrolpacket->dof0_speed*1000)/(int)pow((double)2,(double)z)); Packet[17-z/8]=((int)(720000+armcontrolpacket->dof1_rot*1000)/(int)pow((double)2,(double)z)); Packet[21-z/8]=((int)(720000+armcontrolpacket->dof1_speed*1000)/(int)pow((double)2,(double)z)); Packet[25-z/8]=((int)(720000+armcontrolpacket->dof2_rot*1000)/(int)pow((double)2,(double)z)); Packet[29-z/8]=((int)(720000+armcontrolpacket->dof2_speed*1000)/(int)pow((double)2,(double)z)); Packet[33-z/8]=((int)(720000+armcontrolpacket->dof3_rot*1000)/(int)pow((double)2,(double)z)); Packet[37-z/8]=((int)(720000+armcontrolpacket->dof3_speed*1000)/(int)pow((double)2,(double)z)); Packet[41-z/8]=((int)(720000+armcontrolpacket->dof4_rot*1000)/(int)pow((double)2,(double)z)); Packet[45-z/8]=((int)(720000+armcontrolpacket->dof4_speed*1000)/(int)pow((double)2,(double)z)); Packet[49-z/8]=((int)armcontrolpacket->timestamp/(int)pow(2.0,(double)z)); } if(SendPacket(sock,(char*)&Packet,sizeof(Packet))) return 1; return 0; What would be the easiest way to receive that data, convert it into a readable python format, manipulate them and send them forward to the receiver?

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  • twisted reactor stops too early

    - by pygabriel
    I'm doing a batch script to connect to a tcp server and then exiting. My problem is that I can't stop the reactor, for example: cmd = raw_input("Command: ") # custom factory, the protocol just send a line reactor.connectTCP(HOST,PORT, CommandClientFactory(cmd) d = defer.Deferred() d.addCallback(lambda x: reactor.stop()) reactor.callWhenRunning(d.callback,None) reactor.run() In this code the reactor stops before that the tcp connection is done and the cmd is passed. How can I stop the reactor after that all the operation are finished?

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  • Generate RTT values

    - by Jean Gauthier
    Hi all, I'm writing a Java applet where I should be able to simulate a connection between two hosts. Hence I have to generate packet round-trip times at random. These RTTs can go from ~0 to infinity, but are typically oscillating around some average value (i.e. an extremely large or small value is very improbable but possible). I was wondering if anyone had an idea of how I could do this? Thanks in advance

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  • getnameinfo specifies socklen_t

    - by bobby
    The 2nd arg for the getnameinfo prototype asks for a socklen_t type but sizeof uses size_t. So how can I get socklen_t ? Prototype: int getnameinfo(const struct sockaddr *restrict sa, socklen_t salen, char *restrict node, socklen_t nodelen, char *restrict service, socklen_t servicelen, int flags); Example: struct sockaddr_in SIN; memset(&SIN, 0, sizeof(SIN)); // This should also be socklen_t ? SIN.sin_family = AF_INET; SIN.sin_addr.s_addr = inet_addr(IP); SIN.sin_port = 0; getnameinfo((struct sockaddr *)&SIN, sizeof(SIN) /* socklen_t */, BUFFER, NI_MAXHOST, NULL, 0, 0);

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  • Buffer management for socket application best practice

    - by Poni
    Having a Windows IOCP app............ I understand that for async i/o operation (on network) the buffer must remain valid for the duration of the send/read operation. So for each connection I have one buffer for the reading. For sending I use buffers to which I copy the data to be sent. When the sending operation completes I release the buffer so it can be reused. So far it's nice and not of a big issue. What remains unclear is how do you guys do this? Another thing is that even when having things this way, I mean multi-buffers, the receiver side might be flooded (talking from experience) with data. Even setting SO_RCVBUF to 25MB didn't help in my testings. So what should I do? Have a to-be-sent queue?

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  • What's a way for a client to automatically resolve the ip address of a server?

    - by zooropa
    The project I am working on is a client/server architecture. In a LAN environment, I want the client's to be able to automatically determine the server's address. I want to avoid having to manually configure each client with the ip address of the server. What is the best way to do this? Some alternatives I have thought about doing are: The server could listen for broadcast packets from the clients. The message from the client would be a request for the IP address of the server. The server would respond with its address. The machine running my project's server could also have a bind server running. The LAN's router could be configured to use it as one of its DNS servers. I think I saw that there is a bind library. Does that mean I can build the bind service into my server so that bind doesn't have to be installed on the server? Any other ideas? What have you done in the past? What are the pros/cons of these approaches and others that might be suggested? Thanks for your help!

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