Develop Reference

Cannot get Mosquitto to Allow Connection from Outside Local Network

I have Linux Ubuntu 18.04 laptop, and I installed the Mosquitto MQTT broker there. On my Windows 10 laptop, I am running a C# application written in Visual Studio 2013 that uses the M2Mqtt Libraries.
If I connect via the localhost, everything is fine. I start up the Mosquitto server, connect via the C# application, subscribe to a topic, and then can send messages back and forth all day long.
But when I try to connect through the internet address, I consistently get a uPLibrary.Networking.M2Mqtt.Exceptions.MqttConnectionException:
"No connection could be made because the target machine actively
refused it 95.XXX.XXX.134:1883" error. (The address there is what I got via "WhatsmyIP")
Here's what I have done so far:
First, I went to my router, which is a TP-LINK AC1200. I set the port to forward to the local IP address of the Linux box.
Then I went to my Linux box and used ufw to enable port 1833 and enable the firewall
From there I have tried everything I can think of -- I've run Mosquitto with the port declared at the command line, I have changed the conf file to say:
Listener 1883 0.0.0.0
and
Listener 1883 192.168.0.144
I have removed the port assignment and listener assignment entirely (since that is its default anyway) and always I get the same result.
I downloaded 2 different utilities -- one on an android phone and one is an app available from Windows store, and I cannot connect with either of them, either. The Android phone simply will not connect (it is not on the same network so localhost is not an option) and the other app will connect locally, but not when I change to the internet address.
I get the sense I'm just missing one small thing, but I can't figure out what it is. There are other stackoverflow questions that show the same error, but they don't help me.
If it matters, the actual C# code that is being run is:
try
{
System.Security.Cryptography.X509Certificates.X509Certificate caCert = null;
Boolean useSecureProtocol = false;
int OpenPort = 1883;
// external IP address
String PublicIPAddress = "95.XXX.XXX.134";
// local IP address
String LocalIPAddress = "192.168.0.144";
System.Net.IPAddress ipaddress = System.Net.IPAddress.Parse(PublicIPAddress);
client = new MqttClient(ipaddress, OpenPort, useSecureProtocol, caCert, MqttSslProtocols.TLSv1_0);
// certificate and Protocol are irrelevant because security set to false??
}
catch (System.Net.Sockets.SocketException SException )
{
string SEX = SException.Message;
}
* * *
try
{
Byte retVal = client.Connect(ClientId);
}
catch (uPLibrary.Networking.M2Mqtt.Exceptions.MqttConnectionException ex)
{
string m = ex.Message;
}
Config File: conf.d (which I run explicitly with the -C option)
# Place your local configuration in /etc/mosquitto/conf.d/
#
# A full description of the configuration file is at
# /usr/share/doc/mosquitto/examples/mosquitto.conf.example
#
pid_file /var/run/mosquitto.pid
persistence true
persistence_location /var/lib/mosquitto/
log_dest file /home/mark_admin/mosquitto.log
include_dir /etc/mosquitto/conf.d
As I said, I have changed it and tried many things:
Listener 1883 192.168.0.144
Listener 1883 0.0.0.0
Listener 1883
And none of the above. Just left it blank. None of them worked.

I'm posting this as an answer so I can give more detail in case anyone stumbles upon this in the future.
Setting up the MOSQUITTO MQTT Server in Ubuntu 18.04 is actually not hard, but the steps are important.
Step 1: Install Mosquitto Software
sudo apt-add-repository ppa:mosquitto-dev/mosquitto-ppa
sudo apt-get update
sudo apt-get install mosquitto
Step 2: Open Port 1883 and start firewall
sudo ufw allow 1883
sudo ufw enable
Step 3: Verify Mosquitto is not already running
pgrep mosquitto
[Note, if any number shows, that is the PID of an already running Mosquitto. You can just kill it. Also, you can try: sudo service mosquitto stop]
Step 4: Start Mosquitto with verbose option
mosquitto -v
[Note: This starts Mosquitto without using any config file. It echos connection and status information to the screen. Easiest for quick debugging.]
Step 5: Check connectivity using local host
Go to your client machine (in my case a Windows 10 laptop) and run the MQTT client, connecting to the local address of the Linux Mosquitto server (in my case 192.168.0.144). You should be able to connect. In fact, you can do this step before you even open the firewall, since this is all on the local network, the firewall rules are irrelevant at this point. Until next step which is...
Step 6: Check Connectivity using web tool
use either: www.yougetsignal.com/tools/open-ports/ or
https://canyouseeme.org/
[NOTE: You will not get an OPEN state UNLESS THE MOSQUITTO BROKER IS RUNNING]
Step 7: If Port Shows Closed When coming In from Internet (ie not localhost)
Here's where I got tripped up. In my case, I have a Verizon Modem that ALSO has a firewall (because it has a router). I have my own wireless router, a tp-link Archer C1200, that I have plugged into the Fios Modem/Router. I started by putting the port forwarding in the tp-link. But that firewall comes after the Fios firewall so I needed to go to the first wall and do the port forward there.
And this is the second thing that is tricky. All of the online how-to's said I should forward port 1883 to the local IP address of my Linux Server, which in my case was 192.168.0.144. But that was not correct in my case. The Archer C1200 was actually the device that I needed to forward to -- it handled the correct distribution from there. It had an address of 192.168.0.152 assigned to it from the Verizon router. I still have both forwardings in place (ie the Fios and the tp-link) and my guess is that I need them both.
Now all pathways are open, you can follow the other Mosquitto instructions regarding logging, config files, Daemons, etc.
Hope this saves someone some time down the road!

How can I resolve a "NameResolutionFailure" error when trying to gather data from every type of internet connection?

I am currently using Httpclient and I can successfully gather my data with a specific network/internet-connection at the place that has the data.
However when I try to gather the data at home with another internet-connection I receive an "NameResolutionFailure" error.
My goal is to be able to reach the data from any type of connection but I am not sure what I am quite missing here. (I am also new in this area).
This is the code that I use when I talk to the db:
string dataurl = "my-url-here";
var http = new HttpClientHandler()
{
Credentials = new NetworkCredential("user", "password", "domain"),
};
var httpClient = new HttpClient(http);
try
{
var result = await httpClient.GetStringAsync(dataurl);
System.Diagnostics.Debug.WriteLine(result);
}
catch (HttpRequestException ex)
{
if (ex.GetBaseException() != null)
{
System.Diagnostics.Debug.WriteLine(ex.GetBaseException().Message); //this is where i recieve the NameResolutionFailure error
}
else
{
System.Diagnostics.Debug.WriteLine(ex.Message);
}
}
How come I can only reach the data when I am on a certain network and not with every network? Am I missing code or is there something else in play here?
Appreciate every help, tips, code-examples i can get!

The problem is likely to be in the string dataurl = "my-url-here"; and where that's accessible from. There are likely to be two obstacles:
Name resolution
Network Access
While your error message only mentions Name resolution, I'm guessing you'll need to do something about network access as well.
Name resolution (or DNS) is about translating a host name into an I.P. address.
When you're on a work network, there'll be a name resolution service that resolves local computer names to I.P. addresses on the network. Normally these local computer names are not visible to public DNS servers. If you connect your device to a different network (e.g. a mobile network), it uses the public DNS servers, which know nothing about the local domain named computers.
For example MyServer might resolve on your local network because it's part of your local domain, and the local network infrastructure will sort that out. MyServer.MyCompany.com is usually similar, as by default machines names aren't exposed externally.
For a mobile application, you're going to need a public domain name. Something like MyServer.MyDomain.com (or www.google.com is the same thing, essential). A public DNS server translates this name to an I.P. address.
This is probably where the problem you're experiencing is occurring. You're probably using a local host name, that the public DNS servers don't know about.
If you're working for an organisation they may already have a domain, or you may need to purchase a domain for your application.
In the meantime you could look at one of the dynamic DNS solutions that may allow you to progress for development purposes.
For my Xamarin app, I use the name of the local machine when I'm developing, and the mobile device is on the same network.
If I'm not on the same network, I have a VPN that I can use. This connects into the work network as if I'm on the same network. If I'm developing at home and both devices are on my home network, I use the I.P. address of my development box, because I haven't made local DNS work on my home wifi.
When we go to release we use a public URL, like api.MyApp.com - which public DNS points to our prod server.
Network Access might be a thing that you need to deal with too.
A major part of a Network Engineer's job is to keep the hackers out. When your mobile device is on the same network as the server (i.e. when it's working for you), this isn't a problem because because mostly networks are configured so that two devices on the same network can see each other. It sounds like this is the sort of network you have, if your app can see your server on one connection.
But if you're needing to connect to your server from a mobile network, you need a way to tell your network router to forward specific traffic from the internet to your server.
This gets complicated, but for development purposes, strategies I've seen work are:
A VPN - we have a VPN that I fire up on the mobile device, enter my work network credentials, and then I can access my development box as if I'm on the same network
Virtual server / port forwarding - if you're at home, you can probably configure your modem to forward a particular port to your development box. Every modem is different, so you'd have to search up instructions for your particular one.
Network Engineer - if you're in a corporate, and want traffic from outside to get to a server that you're managing (and don't have a VPN), you probably need to talk to your networks department. Good luck.

C# Dns.GetHostEntry doesn't return names of mobile devices connected to WiFi

I have a windows form application in C# and I'm trying to get the host name of all the clients that I have in a list. Given below is a code example by ra00l from this link: GetHostEntry is very slow (I have a similar code made but this one is cleaner)
private delegate IPHostEntry GetHostEntryHandler(string ip);
public string GetReverseDNS(string ip, int timeout)
{
try
{
GetHostEntryHandler callback = new GetHostEntryHandler(Dns.GetHostEntry);
IAsyncResult result = callback.BeginInvoke(ip,null,null);
if (result.AsyncWaitHandle.WaitOne(timeout, false))
{
return callback.EndInvoke(result).HostName;
}
else
{
return ip;
}
}
catch(Exception)
{
return ip;
}
}
When it's given an IP of a Windows Machine in the network, it shows the correct host name given that you enter a reasonable timeout. After the tests that I made, I didn't get any response for the host names of android and apple devices. For example, the picture below is the DHCP Client List of the router that I have. It shows android, apple and laptop devices. I'm using the laptop 'Nathu-Laptop' giving me an IP address of '192.168.1.106'.
If I enter '192.168.1.105' in the C# function, the result is 'Nandwani-PC' but if I input '192.168.1.103', '192.168.1.104', '192.168.1.101', '192.168.1.100', I don't get any hostname.
I also tried using nbtstat but it only gets the laptops in the network.
When trying this out on my iPod, I ensure that there is a network activity going on. This is to keep the connection alive because it disconnects from the network when it's on standby.
EDIT:
So I found out that DNS.GetHostEntry calls getaddrinfo if IPv6 is enabled, otherwise, call gethostbyaddr and these functions may access the data from \System32\drivers\etc\hosts or maybe from the NETBIOS. The thing is that the NETBIOS is legacy right? but how about for mobile devices?

About NetBIOS:
In order to answer your specific questions about NetBIOS, and name resolution on network, I'll give more details. If you don't have dns server running on your network, name resolution will rely only on NetBIOS resolution.
It is a standard and implemented on several operating systems. However, it's not very fast.
Even if we're old, we're not legacy from the past and obsolete
You can check on Microsoft support the way names are resolved on Windows and NetBIOS is the last one.
However, NetBios name resolution is not always fully functional (like this bug on Android which was fixed in 2014) on all mobile platforms (depends on Android version for example).
If you want to improve the performance, I suggest you to install a DNS server in the network.
Did you try ping -a <IP address> or nslookup <IP address> to check if the results are in line with your expectations ?
If your problem still persist, then you may investigate the .Net implementation, thanks to the above links. You can also check a more up to date version of .Net DNS implementation here

How to mimic an IP Address - Device Simulator Required

I'm new here...been digging around for some help but figured I would join and ask for some guidance.
I'm looking to create an app that can create multiple "fake" devices. They need an IP Address and I'm guessing able to respond to ping. Being able to respond to WMI would also be nice. Kinda like a simulator. I'd like to create up to 50,000 devices but even starting with 1 would help.
What is needed for such an app? TCP Client/Listener? I've never done something like this before so please be gentle :)

You may install Virtual Network Adapter's (driver is included with Windows OS), but i have never used this. Driver for Virtual Network Adapter is here: %WINDIR%\Inf\Netloop.inf
You may use Command line tool called DevCon to add devices by script, like this:
devcon -r install %WINDIR% \Inf\Netloop.inf *MSLOOP
Installation unfortunatelly takes few seconds (on my Core Duo 2.0 laptop).
If you need to configure a lot of network cards you may use command line netsh.
Examples:
netsh in ip set address "Local Area Connection" static 10.0.0.1 255.0.0.0 10.0.0.1 1
netsh in ip add address "Local Area Connection" 10.0.0.2 255.0.0.0
netsh in ip set address "Local Area Connection 2" 10.0.0.3 255.0.0.0
netsh in ip set address "Local Area Connection 3" 10.0.0.4 255.0.0.0
netsh in ip set dns "Local Area Connection" static 10.0.0.250
netsh in ip set wins "Local Area Connection" static 10.0.0.250
You may dump/export current network configuration to a file (to see how current config looks):
netsh interface dump > file.txt
More netsh examples
Edit: removed informations not useful in this case.

If I'm understanding you correctly, unfortunately this will not be easy as you need to virtualize network adapters to do the job you want. an IP address is bound to a nic (physical or logical), not something that can be specified in higher layer code. VMWare Workstation does include a plugin for Visual studio, so perhaps you can use it to generate many virtual nics and assign them ip's programatically, but otherwise you need to write virtual network card drivers (probably in a non-.net language) to do it, if you don't use an existing virtualization tech. you can stack many IP addresses on a nic, but the computer communicating with it will know they are all the same network entity. if thats fine with you, then just add all the IPs you want to the card you have.
on to the second part of your query, since you want the IPs to be able to recieve and send data, their addresses will have to be routable, so you can't just pick any old IP address. if you are fine being behind a NAT wall, you could use 10.x.y.z to address them, but on the outside of the nat they would all appear to be using the same public IP to the outside world. in order to expose 50k publicly routable IP addresses, you would first have to register and buy them.
lastly you can't use TCPClient to do Echo/Ping, since they use the ICMP protocol, but instead use the System.Net and System.Net.NetworkInformation namespace. Here is some VB code to send a ping just to give you the flavor of it:
Imports System
Imports System.Net
Imports System.Net.NetworkInformation
Public Class Pinger
<System.Diagnostics.DebuggerNonUserCode()> _
Public Sub New()
MyBase.New()
'This call is required by the Component Designer.
InitializeComponent()
End Sub
Public Shared Function CanHostBePinged(ByVal IPAddr_DNS_OR_Host_Name As String) As Boolean
Dim p As New Ping
Dim po As New PingOptions
po.Ttl = 256
po.DontFragment = False
Dim stringOut As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZABCDE"
Dim streamOut As Byte() = System.Text.Encoding.ASCII.GetBytes(stringOut)
Try
Dim reply As PingReply = p.Send(IPAddr_DNS_OR_Host_Name, 30, streamOut)
If reply.Status = IPStatus.Success Then
Return True
Else
Return False
End If
Catch ex As Exception
Return False
End Try
End Function
End Class

I know this thread is very old, but I am posting my idea for anyone who might visit this question.
The previous answers already made clear that it is very difficult to achieve what the OP is trying to achieve. But I think if anybody needs such functionality for testing purposes there is a very easy way to achieve it.
We can create a simple web app in Node or .NET or whatever environment is comfortable. The web app's UI will allow us to do the following operations.
Create a device with IP
Mark an IP as Online or Offline.
If IP is online it is pingable, else not.
At the same time, the web app also exposes an API that when supplied with an IP says to us whether the IP is pingable or not. This way we mock the ping operation to an IP. Let's name this web app as PingMock.
Now in the original app, we can create a TestPingService which instead of pinging, sends an HTTP request to PingMock. This way we will be able to test our business logic without having access to actual IPs.
For testing business logic the final output of the PingService matters and not from where the output comes. This is how unit testing is conducted.
The PingMock web app is just an example. We can mock the Ping operation in whichever way we like.

Connection between 2 computers via dial up modem without internet in c#

Hi Is there any way to connecting to computers via Dial Modem without internet?
Like windows Hyper terminal.
making connection sending files between computers.
Just Connection Between two Computers Directly and sending FIle.

Yes.
Assuming the modems are connected via a serial port (or emulate being connected via a serial port): you'll need one modem set up (learn your AT commands!) to listen for and answer incoming calls, and the other to dial the first.
You can then treat the pair as a rather long serial link.
However getting everything to work reliably is more of an art than a science, and something that is so rarely done today that much of it is forgotten. The last time I worked with modems in this way was more than fifteen years ago.

The way we used to do it back in the olden days was with a null-modem cable. We even used to do "networked" gaming that way, back in the day.
This is bascially an RS-232 cable with the receive and transmit pins crosswired. I still see some adapters around, so it shouldn't be too tough to get hold of one.
Much later some people created SLIP (Serial Line IP) to enable a serial line to act as a carrier for the entire TCP/IP stack. A bit later PPP was introduced as an improvement. I think SLIP is still available for most platforms, and PPP exists on every platform that can do dial-up internet.
So if the question basically boils down to wanting to network two computers via PPP without going through somebody else's dial-up server (like Earthlink), what you need is to install a PPP server on one of the two machines. They come with most Linux distros. For Windows you will have to go look. I'd help, but my corporate blocker is being overexuberant again.

Someone has written an XModem implementation in C# here: http://trackday.cc/b2evo/blog2.php/2007/08/02/net-xmodem It may help with what you're after.

One thing that's not clear from your question is whether you are attempting to directly connect two machines in the same physical location with a cable, or if you are attempting to dial in to one from the other over a PSTN.
If they are in the same place, eliminate the modem from the equation. This reduces complexity significantly.
If they are in separate locations (ie, dialing over an honest-to-God dial-up connection), there is some code here that might help you. The article talks about a Bluetooth or GPRS modem, but the core of it is about sending AT commands which can be used to talk to any AT-command set-compatible device. It might get you going in the right direction.
Update
See http://msdn2.microsoft.com/en-us/system.io.ports.serialport(VS.80).aspx
Since a modem should be attached to a COM port (COM1-COM12) even it is an internal modem, you should be able to use the .NET framework's SerialPort class to open the port, send AT commands, etc. Once you have an open connection, you could use the XModem library to transfer files, or straight serial for regular communications.
Do you need an IP stack, or are you happy with a straight serial protocol?

You can quite easily setup dial-up network connections within Windows that require the use of a modem (its under the option for setting up a VPN, but you can set it for just a dial up).
So I would assume that you can then map a network location to it for use by your C# code.
As already stated at least one of the modems must be on and listening for a connection.
* edit *
I believe that the following code will trigger a dial-up connection that has been placed within Network Connections
System.Diagnostics.ProcessStartInfo procStartInfo = new System.Diagnostics.ProcessStartInfo(#"c:\Local Area Connection 2 - Shortcut");
System.Diagnostics.Process proc = new System.Diagnostics.Process();
proc.StartInfo = procStartInfo;
proc.Start();
For link placed at c:\ drive and named "Local Area Connection 2 - Shortcut"
You could then ping the destination to see if its connected.
Ultimately though I think that your best solution may be to use RAS.
Have a look here at Codeplex: DotRAS
You can then use the following code:
RasDialer dialer = new RasDialer();
bool connected = false;
foreach (RasConnection connection in dialer.GetActiveConnections())
{
if (connection.EntryName == "MyFriendsPC")
{
connected = true;
break;
}
}
if (!connected) {
dialer.EntryName = "MyFriendsPC";
dialer.Dial();
// If you need to provide credentials, use the Dial(NetworkCredential) overload that's available.
}
This example assumes you already have an entry named MyFriendsPC in the default phone book. If you do not and need to create this connection programmatically, you can use the RasPhoneBook component for that.
RasPhoneBook pbk = new RasPhoneBook();
pbk.Open(); // This will open the phone book in the All Users profile.
RasEntry entry = new RasEntry("MyFriendsPC");
If you'd rather use the default settings for the connection you can use one of the static methods on the RasEntry class, or manually configured the connection here.
pbk.Entries.Add(entry);
Once the entry has been added to the collection, it will immediately be added into the phone book.

I recently wanted to connect a dial-up POS terminal to an analog modem. This is not difficult, but you need to introduce a 9-volt battery and a 200mA resistor in parallel for the modems to connect. https://www.youtube.com/watch?v=luarFqislIc describes the approach (skip to 11:30 to see the circuit). Without the battery and resistor to provide the loop current (about 18mA), the modems will not negotiate a connection (you'll hear the modem after entering ATA to answer, but you won't hear the final part of the modem negotiation). With the loop current, the modems will connect. The video even shows ZModem being used to transfer a file from one PC to the other.
One final item not mentioned in the video is with this circuit, there is no dial tone. To get around this, enable blind dialing (ATX1) on the calling modem. Also, since there are no rings with this approach, setting the receiving modem to auto-answer (ATS0=1) won't work. You have to enter ATA on the receiving modem to answer.