I'm new to java networking. My scenario here is 2 client computers are connecting to a server hosted in LAN. So I use NetworkServerControl API to start the host:
private static void startServer(){
try{
NetworkServerControl nsc = new NetworkServerControl(InetAddress.getByName("localhost"), 1527);
nsc.start(null);
}catch(Exception e){
JOptionPane.showMessageDialog(null, "Start network error : " + e.getMessage());
}
My questions are:
1) Is localhost accessible by computers in LAN?
- If yes, I tried to use ij to connect derby database in the server but it wrote connection refused. Anything I missed out?
ij: CONNECT 'jdbc:derby://localhost:1527/c:/app_db/' user 'xxx' password 'xxx';
- If no, what is the common approach should be used? Please guide me the right track.
Thanks.
To access your Derby database from other machines on the network, you need to change "localhost" to a different value. You can give the DNS name of your machine, or the public IP address of your machine.
Note that you have to make this change both on the Derby server and on each of the client URLs.
You should be able to use netstat -a to confirm the effects of your changes on the server.
Related
I try to get remote (client) IP addres:
var ip = httpContext.Features.Get<IHttpConnectionFeature>()?.RemoteIpAddress
But it works only for local requests (it will return ::1 value)
When I load page from remote machine the value is null. I investigated there is no IHttpConnectionFeature in the Features collection in this case.
Why? And how to get remote ip address correctly?
I know that this post is old but I came here looking for the same question and finnaly I did this:
On project.json add dependency:
"Microsoft.AspNetCore.HttpOverrides": "1.0.0"
On Startup.cs, in the Configure method add:
app.UseForwardedHeaders(new ForwardedHeadersOptions
{
ForwardedHeaders = ForwardedHeaders.XForwardedFor |
ForwardedHeaders.XForwardedProto
});
And, of course:
using Microsoft.AspNetCore.HttpOverrides;
Then, I got the ip like this:
Request.HttpContext.Connection.RemoteIpAddress
In my case, when debugging in VS I got always IpV6 localhost, but when deployed on an IIS I got always the remote IP.
Some useful links:
How do I get client IP address in ASP.NET CORE? and RemoteIpAddress is always null
The ::1 may be because:
Connections termination at IIS, which then forwards to Kestrel, the v.next web server, so connections to the web server are indeed from localhost.
(https://stackoverflow.com/a/35442401/5326387)
Just try this:
var ipAddress = HttpContext.Connection.RemoteIpAddress;
And if you have another computer in same LAN, try to connect with this pc but use user ip instead of localhost. Otherwise you will get always ::1 result.
I've written a tool that validates emails, mostly copied from various examples on the subject around on the internet (user Don Worthley compiled a decent collection of code samples here https://delicious.com/dworthley/email.validation). Unfortunately after creating the socket and the IPEndPoint from the email to verify's hostname IP and port, my code always fails to connect to the socket due to timeout.
Here is the pertinent code (fails at s.Connect(endPt) due to timeout):
private bool smtpCheckEmail(string email)
{
try
{
string[] host = (email.Split('#'));
string hostname = host[1];
IPHostEntry IPhst = Dns.GetHostEntry(hostname);
IPEndPoint endPt = new IPEndPoint(IPhst.AddressList[0], 25);
using (Socket s = new Socket(endPt.AddressFamily, SocketType.Stream, ProtocolType.Tcp))
{
try
{
s.Connect(endPt);
}
catch
{
s.Close();
return false;
}
From my research others have reported success with similar code so it might be an issue with my server host. The MVC project is on a GoDaddy VPS with Windows 7 and standard firewall/MSSE as protection (I've tested with both disabled with same timeout result).
I've verified I can telnet to my own host and run through the various HELO, Mail from etc commands but it also times out if I try to connect to smtp for other hosts.
Maybe it's an ISP issue?
I've also tried installing EmailVerify for .NET trial but run into the same problem where any validation at or above SMTP check times out.
Would be great to get some suggestions of what might be the problem and how to troubleshoot it.
Edit: After doing some comparison testing with one of my Azure VPS it looks like it is likely to be server related, "telnet 74.125.206.108 smtp" (gmail's smtp host IP) through command line connects on the Azure box but not on the GoDaddy one my project is on.
I also notice that when my code pulls the IP from the host name (Dns.GetHostEntry(hostname)), in this gmail example it returns 216.58.216.37 which matches what I get if a run nslookup in cmd for gmail.com, however the IP for smtp that I can telnet to is for gmail is 74.125.206.108 which matches the nslookup record for smtp.gmail.com. Could my code be grabbing the wrong IP addresses in many cases here?
Turned out to be a limitation of GoDaddy VPS. Transferred code to an Azure hosted project and it worked great.
Occasionally I get this error when working on remote computers. It's hit or miss on which computer I get it on. But I am able to ping the computer and test-connection pans out. For example, the computer I got this error on today I was able to get to yesterday. I know the computer is on because It's right next me.
Get-WmiObject : The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
At line:1 char:14
+ get-wmiObject <<<< -Class win32_operatingsystem -ComputerName $current -Authentication 6 -credential $credential | Invoke-WMIMethod -name Win32Shutdown
+ CategoryInfo : InvalidOperation: (:) [Get-WmiObject], COMException
+ FullyQualifiedErrorId : GetWMICOMException,Microsoft.PowerShell.Commands.GetWmiObjectCommand
Check to see if the Remote Procedure Call (RPC) service is running. If it is, then it's a firewall issue between your workstation and the server. You can test it by temporary disabling the firewall and retrying the command.
Edit after comment:
Ok, it's a firewall issue. You'll have to either limit the ports WMI/RPC work on, or open a lot of ports in the McAfee firewall.
Here are a few sites that explain this:
Microsoft KB for limiting ports
McAfee site talking about the same thing
You may get your answer here: Get-WmiObject : The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
UPDATE
It might be due to various issues.I cant say which one is there in your case. It may be because:
DCOM is not enabled in host pc or target pc or on both
your firewall or even your antivirus is preventing the access
any WMI related service is disabled
Some WMI related services are:
Remote Access Auto Connection Manager
Remote Access Connection Manager
Remote Procedure Call (RPC)
Remote Procedure Call (RPC) Locator
Remote Registry
For DCOM settings refer to registry key HKLM\Software\Microsoft\OLE, value EnableDCOM. The value should be set to 'Y'.
My problem turned out to be blank spaces in the txt file that I was using to feed the WMI Powershell script.
I had the same problem when trying to run a PowerShell script that only looked at a remote server to read the size of a hard disk.
I turned off the Firewall (Domain networks, Private networks, and Guest or public network) on the remote server and the script worked.
I then turned the Firewall for Domain networks back on, and it worked.
I then turned the Firewall for Private network back on, and it also worked.
I then turned the Firewall for Guest or public networks, and it also worked.
Duting create cluster, my error was:
An error occurred while creating the cluster.
Could not determine Management Point Network Type.
The RPC server is unavailable
Solution:
Server Manager
Local Server
Click on one of the network adapter links, like "Ethernet".
Control Panel\Network and Internet\Network Connections
Right click on the first network adapter
Internet Protocol Version 4 (TCP/IPv4)
Properties
Advanced
DNS
Click radio button:
Append primary and connection specific DNS suffixes
If anyone else is reading this eons later. My problem was I deployed a GPO a few months ago that disables printer spooling via Windows Firewall rules. One of the rules is "File and printer sharing (Spooler Service - RPC-EPMAP)". This was set to deny.
This blocked the "RPC Endpoint Mapper" port range inbound and didn't specify a service. As a result this was blocking all traffic inbound on all RPC ports (tcp 1024-5000).
Disables the rule and this magically started working again.
TLDR; You need to allow the RPC Endpoint Mapper port range inbound on Windows firewall (tcp 1024-500) along with the WMI-In rule.
I have a chat server that i create for my window phone app. Right now it working on my local computer, how do i make it online so everyone can connect to it.
Chat server:
TcpListener chatServer = new TcpListener(4296);
Chat client:
TcpClient client = new TcpClient("127.0.0.1", 4296);
How do i forward the port so i can host it online!
In order for the world to see it you need to host it somewhere with a public IP address. You will then use this IP address in the client connection:
Chat client: TcpClient client = new TcpClient("xxx.xxx.xxx.xxx", 4296);
Depending on your platform you could use Google App Engine or Amazon Web Services to quickly deploy your application.
That depends on your router/gateway. Check your router's documentation for more information how to forward ports.
Basically If you want to deploy your app online you need your own Domain(you get your own IP to host), you can use Cloud Server to deploy(these is a good option, since you can deploy for free but storage is limited in free edition), Or else you can Host on your Routers IP Address.
If you are using first two option then these is a python script to start a listener service on given IP and port.
Here:
import socket
import sys
HOST ='' # Symbolic name, meaning all available interfaces
PORT = 8000 # Arbitrary non-privileged port
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created'
try:
s.bind((HOST, PORT))
except socket.error as msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit()
print 'Socket bind complete'
#Start listening on socket
s.listen(10)
print 'Socket now listening'
#now keep talking with the client
while 1:
#wait to accept a connection - blocking call
conn, addr = s.accept()
print 'Connected with ' + addr[0] + ':' + str(addr[1])
s.close()
These is just a sample, you can put all of Your code from Your PC to Cloud and edit the changes in IP.
And if you want your router to listen to the client then you have to go to the routers login page, for most of the router it is 192.168.51.1, go here and login as administrator, Then you should go to firewall configuration over there you will find an option of custom server, then click on it and then there configure the ip address, port,etc to host.
I prefer you to watch these full video to understand properly: Here Video
In these video he is hosting for exploitation purpose you can host to do any other activity.
Thank You.
In advance, thank you for your advice.
I am currently working on a program which uses Putty to create a SSH connection with a server that uses local port forwarding to enable a client, running my software, to access the service behind the SSH server via localhost.
IE: client:20100 -> Internet -> Remote SSH server exposed via router/firewall -> Local Intranet -> Intranet Web POP3 Server:110.
Cmd Line: "putty -ssh -2 -P 22 -C -L 20100:intranteIP:110 -pw sshpassword sshusername#sshserver"
Client would use putty to create a SSH connection with the SSH server specifying in the connection string that it would like to tie port 110 of the Intranet POP3 Server to port 20100 on the client system. Therefore the client would be able to open up a mail client to localhost:20100 and interact with the Internal POP3 server over the SSH tunnel. The above is a general description. I already know what I am trying to do will work without a problem so am not looking for debate on the above.
The question is this...How can I ensure the local port (I cannot use dynamic ports, so it must be static) on localhost is not being used or listened to by any other application?
I am currently executing this code in my C# app:
private bool checkPort(int port)
{
try
{
//Create a socket on the current IPv4 address
Socket TestSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
// Create an IP end point
IPEndPoint localIP = new IPEndPoint(IPAddress.Parse("127.0.0.1"), port);
// Bind that port
TestSocket.Bind(localIP);
// Cleanup
TestSocket.Close();
return false;
}
catch (Exception e)
{
// Exception occurred. Port is already bound.
return true;
}
}
I am currently calling this function starting with a specific port in a for loop to get the 'false' return at the first available port. The first port I try is actually being listened to by uTorrent. The above code does not catch this and my connection fails.
What is the best method to ensure a port is truly free? I do understand some other program may grab the port during/after I have tested it. I just need to find something that will ensure it is not currently in use AT ALL when the test is executed.
If there is a way to truly reserve the localhost port during the test, I would love to hear about it.
Here's the answer how to check if local port is free.
I would recommend this way:
bool IsBusy(int port)
{
IPGlobalProperties ipGP = IPGlobalProperties.GetIPGlobalProperties();
IPEndPoint[] endpoints = ipGP.GetActiveTcpListeners();
if ( endpoints == null || endpoints.Length == 0 ) return false;
for(int i = 0; i < endpoints.Length; i++)
if ( endpoints[i].Port == port )
return true;
return false;
}