Good day everyone!
I am making a DHCP Server for a project. I tried it in Windows and it worked. Now, I need to make it work on Linux. I used the same code and it can listen packets coming from port 67. However, every time I am about to send packets to the machine in KVM (Kernel Virtual Machine), I get an error at line containing "datagramsocket.send(response)" saying that Network is Unreachable. Btw, I am using a centOS as host and another centOS as guest machine. Bridge connection and firewall is disabled. How could I fix this problem? I am clueless.
Thanks in advance! :)
I used a dhcp4java API and here's a portion of my code:
if (replypacket != null){
InetAddress add = replypacket.getAddress();
int port = replypacket.getPort();
byte[] buf = replypacket.serialize();
DatagramPacket response = new DatagramPacket(buf, buf.length, add, port);
datagramsocket.send(response);
}
Related
I am trying to make a connection from a server running Ubuntu to a Beckhoff PLC with TwinCAT 3. With Windows everything works fine but with the same server on Linux I can't get a connection.
The Linux server has a static IP and in the route manager in the PLC I can find the route and see the server. I have tried adding the route by the route manager in the PLC and with "add_route_to_plc" but both ways my connection is refused. I have already turned off all firewalls. Any of you guys any idea what goes wrong here? In the attachment I have added some picture to see my settings and code that I try to run.
Python error: "connection closed by remote"
Python code:
import pyads
SENDER_AMS = '192.168.1.180.1.1'
PLC_IP = '192.168.1.100'
PLC_USERNAME = 'Administrator'
PLC_PASSWORD = '1'
ROUTE_NAME = 'GID_TEST_ROUTE'
HOSTNAME = 'Grid-stabilizer'
pyads.open_port()
pyads.set_local_address(SENDER_AMS)
pyads.add_route_to_plc(SENDER_AMS, HOSTNAME, PLC_IP, PLC_USERNAME, PLC_PASSWORD, route_name=ROUTE_NAME)
pyads.close_port()
plc=pyads.Connection('192.168.1.100.1.1', pyads.PORT_TC3PLC1)
plc.open()
plc.read_state()
If you are running python on linux and the plc on windows try
plc=pyads.Connection('192.168.1.100.1.1', pyads.PORT_TC3PLC1, PLC_IP)
This will create a route on the linux system. In your code the ip is missing to create a proper route.
Check the port of your plc. It should be 851.
I want to write simple application that communicates between the Hyper-V host and its virtual machine using Hyper-V sockets (netcat over vsock). In the Internet there are a few documents describing how to do it: Make your own integration services, Practical Hyper-V socket communication. However, any of them helps me to achieve my goal.
First of all, I've made sure that the connection using Hyper-V sockets is possible. On the guest Linux I loaded hv_sock module and run nc-vsock application which is able to listen on vsocks:
$ sudo modprobe hv_sock
$ nc-vsock -l 1234
On Windows in PowerShell I ran hvc, which utilises Hyper-V sockets and is able to emulate netcat:
hvc nc -t vsock little-helper 1234
and it works. I can see data sent from server to client and vice versa.
Then I wrote a simple application basing on 1 and 2 with slight changes.
I registered my application with the Hyper-V Host's registry as said in 1 and I ran my application. The connection was not established and the connect function returned error 10049.
I've tried to run my application as a administrator and manipulate GUIDs in the source code and on the Hyper-V Host's registry as well. However, nothing helps and application always reports error 10049.
In my opinion in the document are some ambiguity. E.g. it's said that the service id shall be a random GUID. But later on there is a note that the first four octets translate to port in AF_VSOCK address family, and the specific GUID is presented for this purpose.
Question is rather simple: what I did wrong or misunderstood. Is it possible to write netcat utilising vsock between Windows and Linux?
Full code:
#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <hvsocket.h>
#include <combaseapi.h>
int main()
{
struct __declspec(uuid("00000000-185c-4e04-985a-4c2eee3e03cc")) VSockTemplate {};
struct __declspec(uuid("2a9fa68e-4add-45cb-85c8-de97fc66d388")) ServerVsockTemplate {};
//----------------------
// Initialize Winsock
WSADATA wsaData;
int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != NO_ERROR) {
wprintf(L"WSAStartup function failed with error: %d\n", iResult);
return 1;
}
//----------------------
// Create a SOCKET for connecting to server
SOCKET ConnectSocket;
ConnectSocket = socket(AF_HYPERV, SOCK_STREAM, HV_PROTOCOL_RAW);
if (ConnectSocket == INVALID_SOCKET) {
wprintf(L"socket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// The sockaddr_in structure specifies the address family,
// IP address, and port of the server to be connected to.
SOCKADDR_HV clientService;
clientService.Family = AF_HYPERV;
clientService.VmId = __uuidof(ServerVsockTemplate);
clientService.ServiceId = __uuidof(VSockTemplate);
clientService.ServiceId.Data1 = 1234;
//----------------------
// Connect to server.
iResult = connect(ConnectSocket, (SOCKADDR*)&clientService, sizeof(clientService));
if (iResult == SOCKET_ERROR) {
wprintf(L"connect function failed with error: %ld\n", WSAGetLastError());
iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR)
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
wprintf(L"Connected to server.\n");
iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR) {
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
WSACleanup();
return 0;
}
For whoever is not very familiar with Hyper-V and does not want to spend 2 hours debugging, like I did, a few points:
Ensure that the hv_sock kernel module is enabled on the guest, I used Ubuntu Server 20.04, which does not have this enabled by default.
lsmod | grep hv_sock
If it's not there you need to add it and reboot:
sudo sh -c 'echo "hv_sock" > /etc/modules-load.d/hv_sock.conf'
sudo reboot
You need to register a new application with Hyper-V Host's registry, but the docs are misleading, as the random GUID is only needed with a Windows guest, for Linux guests the GUID needs to be in a very specific format, as described by HV_GUID_VSOCK_TEMPLATE, meaning <port>-facb-11e6-bd58-64006a7986d3
So for port 5001 the registry key should be 00001389-facb-11e6-bd58-64006a7986d3 (1389 is 5001 in hex)
You can do that easily from powershell as described in the Register a new application section
$service = New-Item -Path "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization\GuestCommunicationServices" -Name "00001389-facb-11e6-bd58-64006a7986d3"
$service.SetValue("ElementName", "HV Socket Demo")
You can find some simple code samples here, win_server.c for the Windows host and wsl_client.c for the Linux guest.
What is the ServerVsockTemplate GUID you have there? I'm pretty sure that's supposed to be the GUID of a running VM, e.g., (Get-VM -Name $VMName).Id, so it'd be hard to hard-code into your source. If that's the GUID you generated per 'Register a new application', that'll be the problem.
The docs aren't clear, but I have the strong suspicion that 'Register a new application' part is only for when you're listening on Windows for incoming connections from other Windows VMs, or when writing a Linux device driver that talks to a service on the host. It might also be to allow a VM to offer services to other VMs, but I would assume not.
Edit: Quick Testing VSOCK (Hyper-V) Support in X410 says you need to make the registry keys for the vsock GUIDs as well, to receive connections from the vm.
In Linux userspace, you only have access to vsock; the other services are managed by drivers under Linux.
There's a clearer explanation of the vsock workflow in the Linux source for the Hyper-V vsock implementation.
I assume it's possible to use VSock between a Windows VM and the host as well, of course.
Edit, because I actually went and tested this.
Two mistakes in the code, on top of the ServerVsockTemplate GUID needing to be the GUID of the target VM.
The VSockTemplate GUID is wrong. I don't know where that came from, but there's a constant HV_GUID_VSOCK_TEMPLATE in <hvsocket.h> anyway, which matches the one on the Microsoft Docs site: 00000000-facb-11e6-bd58-64006a7986d3
It turns out, you need to zero the Reserved member of the SOCKADDR_HV, or it'll fail. Traditionally, one would use memset to zero a new sockaddr_* structure, but in this case, we can take the easy path.
So to make this work, change the SOCKADDR_HV creation code to the following:
// The sockaddr_in structure specifies the address family,
// IP address, and port of the server to be connected to.
SOCKADDR_HV clientService;
clientService.Family = AF_HYPERV;
clientService.Reserved = 0;
clientService.VmId = __uuidof(ServerVsockTemplate);
clientService.ServiceId = HV_GUID_VSOCK_TEMPLATE;
clientService.ServiceId.Data1 = 1234;
Then you delete VSockTemplate, and make sure ServerVsockTemplate is the GUID of the VM or Micro-VM where you're running nc-vsock.
I actually tested this with the WSL2 micro-VM, for which the VM ID comes from hcsdiag list rather than Get-VM, but I was able to connect to nc-vsock inside my WSL2 session using the source here, modified as I have described.
I am doing a program about client server communication using sockets. I saw examples of client server program on internet, but I have a question. How to get host name? I saw a client program example on the webpage int the link below. The program gets the host name from the user in command line arguments,but how can I know the host name? and I tried using my username on it but its says host does not found. I am running both on same machine. Thank you very much for your time.
client:
http://www.tutorialspoint.com/unix_sockets/socket_client_example.htm
server:
http://www.tutorialspoint.com/unix_sockets/socket_server_example.htm
Host name is different from the username to get the host name use the command "hostname"
and use this host name in command line
commands:
hostname -->gethostname
hostname < name > -->sethostname with name
If your client and server are on the same host, the hostname is localhost, or you could use the name of the machine, or you could use 127.0.0.1
Assuming you mean the host you are currently running on you use gethostname
int main(int argc, char *argv[])
{
int ret;
char buffer[100];
if ((ret = gethostname(buffer, sizeof(buffer))) == -1)
{
perror("gethostname");
exit(1);
}
printf("hostname is: %s\n", buffer);
return(0);
}
For a client server program , the client must know the hostname or the ip address of the machine it wants to communicate with.
Think of it like you are driving to a particular shop, you need to know the address of the shop to reach there. Similarly clients need the address of the host it needs to communicate with.
If you are running your own client and server, then type hostname in the machine and it will give you the host name. Usually you would need host name and port but in simple example programs the value may be hard coded.
I am setting up a small local network with 3 laptops. My goal is to experiment with the UpNP protocol and have the laptops discover each other using UpNP. In order to do this, they need to be able to listen for notifications from each other. As per the protocol, these notifications are sent on multicast address 239.255.255.250:1900. However, I am having a problem setting the laptops up to listen on that address. I am starting just using 1 pc. My PC's IP address is 10.0.0.5.
However, when I try to set up a UdpClient to listen on 239.255.255.250:1900 I get an error saying: "The requested address is not valid in its context".
I have tried just setting it up using this:
IPEndPoint endpoint = new IPEndPoint(IPAddress.Parse("239.255.255.250"), 1900);
UdpClient client = new UdpClient(endpoint);
client.BeginReceive(MessageReceived, null);
I have also tried:
UdpClient client = new UdpClient(Port);
client.JoinMulticastGroup(IPAddress.Parse("239.255.255.250"));
client.BeginReceive(MessageReceived, null);
But I still get the same error: "The requested address is not valid in its context".
How do I correctly set up my UdpClient to listen on the multicast address 239.255.255.250:1900 ?
Thanks for your help!!!
Ok, after much searching and banging my head on my desk, I've got this thing working. I thought I had it working yesterday, but it only worked on Windows 7 and not on XP..
So, here it goes:
IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Any, Port);
UdpClient client = new UdpClient();
client.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
client.Client.Bind(localEndPoint);
client.JoinMulticastGroup(IPAddress);
client.MulticastLoopback = true;
Client.BeginReceive(MessageReceived, null);
I sure wish this was documented a bit better, but I guess that's why we get the big bucks $$$.
Thanks StackOverflow for providing such an AWESOME knowledgebase from which to extract this stuff !!
I have a WebLogic 11g domain with 1 admin server and 4 managed servers running on 2 machines. Each machine has 3 ip addresses, but only one of those addresses is seen by another machine. Each machine is running a node manager which seems to communicate fine between each other and admin server. Though when managed server starts on the second machine it can't communicate to admin server because it uses wrong ip address. It appears that when weblogic starts it maps itself to all ip addresses, but selects wrong one as the first one i.e. default. That's why managed servers recieve wrong information from node manager.
Is there a way to set preffered listen address in weblogic 11g, but still allow it to listen to all other addresses either? How does weblogic get list of ip addresses? Is the order of them OS-dependent?
Does this answer the question? I believe if you play with the scripts in /etc/sysconfig, you'll affect the loading order and thence the enumeration order. I must admit, I don't have a RH box here to confirm that suspicion.
Weblogic uses the NetworkInterface.getNetworkInterfaces() method and his own logic to set the order of the listen addresses. This logic is changed from 10.3.2 to 10.3.4.
The relevant code is in the method getAllAddresses of the class weblogic.server.channels.AddressUtils$AddressMaker in weblogic.jar
You can check the order with a simple test:
import java.net.*;
import weblogic.server.channels.*;
public class TestIP_WLS {
public static void main(String args[]) throws UnknownHostException {
System.out.println("=== AddressUtils.getIPAny()");
InetAddress addrs[] = AddressUtils.getIPAny();
for (InetAddress addr : addrs) {
System.out.println("*** " + addr);
}
}
}