While executing a load test within Visual Studio I keep hitting the following error:
SocketException Only one usage of each socket address
(protocol/network address/port) is normally permitted x.x.x.x:443
once I ramp up to a certain number of users. Now I have adjusted the registry settings regarding the MaxUserPort (to 65534) and the TcpTimedWaitDelay (to 30) and this has made no difference.
This is Visual Studio 2012 on Windows Server 2012.
Does anyone have any suggestions?
At a guess, since you haven't provided enough information, you are binding and connecting outbound sockets, and you are trying to re-use local port numbers. You can't do that. Get rid of the bind step and let the system allocate the local port number. However you will then discover that you still run out of ports with a bind error, or possibly this is the bind error, and this is because using a single client program as a server load test is fundamentally invalid. Your only recourse is to use fewer connections and more client hosts as well.
Related
Summary:
I am guessing that the issue here is something to do with how Windows and Linux handle TCP connections, or sockets, but I have no idea what it is. I'm initiating a TCP connection to a piece of custom hardware that someone else has developed and I am trying to understand its behaviour. In doing so, I've created a .Net core 2.2 application; run on a Windows system, I can initiate the connection successfully, but on Linux (latest Raspbian), I cannot.
It appears that it may be because Linux systems do not try to retry/retransmit a SYN after a RST, whereas Windows ones do - and this behaviour seems key to how this peculiar piece of hardware works..
Background:
We have a black box piece of hardware that can be controlled and queried over a network, by using a manufacturer-supplied Windows application. Data is unencrypted and requires no authentication to connect to it and the application has some other issues. Ultimately, we want to be able to relay data from it to another system, so we decided to make our own application.
I've spent quite a long time trying to understand the packet format and have created a library, which targets .net core 2.2, that can be used to successfully communicate with this kit. In doing so, I discovered that the device seems to require a kind of "request to connect" command to be sent, via UDP. Straight afterwards, I am able to initiate a TCP connection on port 16000, although the first TCP attempt always results in a RST,ACK being returned - so a second attempt needs to be made.
What I've developed works absolutely fine on both Windows (x86) and Linux (Raspberry Pi/ARM) systems and I can send and receive data. However, when run on the Raspbian system, there seems to be problems when initiating the TCP connection. I could have sworn that we had it working absolutely fine on a previous build, but none of the previous commits seem to work - so it may well be a system/kernel update that has changed something.
The issue:
When initiating a TCP connection to this device, it will - straight away - reset the connection. It does this even with the manufacturer-supplied software, which itself then immediately re-attempts the connection again and it succeeds; so this kind of reset-once-then-it-works-the-second-time behaviour in itself isn't a "problem" that I have any control over.
What I am trying to understand is why a Windows system immediately re-attempts the connection through a retransmission...
..but the Linux system just gives up after one attempt (this is the end of the packet capture..)
To prove it is not an application-specific issue, I've tried using ncat/netcat on both the Windows system and the Raspbian system, as well as a Kali system on a separate laptop to prove it isn't an ARM/Raspberry issue. Since the UDP "request" hasn't been sent, the connection will never succeed anyway, but this simply demonstrates different behaviour between the OSes.
Linux versions look pretty much the same as above, whereby they send a single packet that gets reset - whereas the Windows attempt demonstrates the multiple retransmissions..
So, does anyone have any answer for this behaviour difference? I am guessing it isn't a .net core specific issue, but is there any way I can set socket options to attempt a retransmission? Or can it be set at the OS level with systemctl commands or something? I did try and see if there are any SocketOptionNames, in .net, that look like they'd control attempts/retries, as this answer had me wonder, but no luck so far.
If anyone has any suggestions as to how to better align this behaviour across platforms, or can explain the reason for this difference is at all, I would very much appreciate it!
Nice find! According to this, Windows´ TCP will retry a connection if it receives a RST/ACK from the remote host after sending a SYN:
... Upon receiving the ACK/RST client from the target host, the client determines that there is indeed no service listening there. In the Microsoft Winsock implementation of TCP, a pending connection will keep attempting to issue SYN packets until a maximum retry value is reached (set in the registry, this value defaults to 3 extra times)...
The value used to limit those retries is set in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\TcpMaxConnectRetransmissions according to the same article. At least in Win10 Pro it doesn´t seem to be present by default.
Although this is a conveniece for Windows machines, an application still should determine its own criteria for handling a failed connect attempt IMO (i. e number of attempts, timeouts etc).
Anyhow, as I said, surprising fact! Living and learning I guess ...
Cristian.
I'm trying to establish a connection using sockets between 2 PC's on the same LAN using the Eiffel Programming Language. I'm trying to run the examples that are by default on the installation directory of Eiffel Studio. However right now I'm trying to make it on the same machine by addressing to localhost (127.0.0.1).
It works perfectly on Linux (Ubuntu 15.10) but on windows 7 I'm getting an exception when I try to run the client program. The code of the exception is 24 Unable to establish connection. The server program runs just fine and I already got a connection between a client on linux and a server on windows. I didn't find a solution to this exception on the documentation nor on other sites. Here is a screencap:
Screencap of the debugger
Here is a link to the doc:
https://www.eiffel.org/doc/solutions/Two%20Machines
Thank you in advance.
The issue might be caused by the fact that some ports are used and others are reserved by the system. In particular the port range 0-1023 is designated for use by common system and network services. Ports beyond this range can also be registered (e.g., Service Name and Transport Protocol Port Number Registry or List of TCP and UDP port numbers). System security settings could also prevent applications from using specific port numbers.
The solution is to look for and to use port numbers that are available for user applications. Ports currently used on Windows can be found with netstat -an, what can be used is related to TCP/IP and firewall settings. The simplest approach is to try using some other port numbers, e.g. in the range 1024-49151.
I am trying to bind a HttpWebRequest call to a specific IP on my server (which has many IPs). I have successfully written this code using BindIPEndPointDelegate and it works well on my local machine (Windows 7)
My issue is with Windows Server 2008. When I run the same console app on Windows Server 2008 it fails to bind to the IP when using the delegate. To complicate matters further, it seems to work for some destination URLs (http://www.microsoft.com) and doesn't work for some (http://www.google.com, http://www.facebook.com)
If I remove the IP specific binding (delegate) and run the app it works for all URLs.
The IP I am binding to is the default server IP address - meaning, in both scenarios the same IP should be used. I have verified this and it uses the same IP if I don't bind using the delegate. If I explicitly specific the IP it fails as described above.
I have tried turning off firewall, IIS & Antivirus - the problem persists.
Alright finally figured it out.
Upon testing again I found that specifying IPAddress.Any did not work either. On the other hand, IPAddress.IPv6Any worked fine.
Finally, I unchecked the IPv6 protocol in network adapter settings and the app starting working properly for all URLs and binding for all local IPv4 addresses.
Not sure if this is a bug in .NET code or feature - but disabling IPv6 fixed it for me.
Lastly, if anyone is facing "The requested address is not valid in its context" while making calls with binding, try disabling your antivirus.
A little background:
I have a Windows .NET application that is in use by approximately 40 field employees across North America. This program allows the users to enter data while in the field (away form internet access) and then synchronizes to our Sql Server 2005 database at night. A couple days ago, two of my users reported getting the following error when they performed an action that would attempt to connect to our server database (which uses .NET's SqlConnection class).
System.Data.SqlClient.SqlException: A
network-related or instance-specific
error occurred while establishing a
connection to SQL Server. The server
was not found or was not accessible.
Verify that the instance name is
correct and that SQL Server is
configured to allow remote
connections. (provider: Named Pipes
Provider, error: 40 - Could not open a
connection to SQL Server)
Our field employees are typically operating on a hotel Wi-Fi connection, and at first I thought that they both coincidentally got on an "uncooperative" network the same day. The following day, having moved to different hotels, the problem went away for one of these users, but continued for the other.
Besides providing the error message, the purpose of this background is to point out that
this is the first time this issue has occurred in over a year of using this software, and
the majority of our users aren't having any problem connecting to our server database with the same software.
This makes me hesitate to think that the issue is at the server (most forums and blogs I've read on this error provide steps to ensure the SQL Server is configured properly).
Noticing the Named Pipes Provider portion of the error message, I guessed that maybe this user's computer or network was causing it to attempt connection via pipes rather than TCP, so I did try configuring the server to allow BOTH TCP/IP and Named Pipes for remote connections, where it was previously set to TCP/IP only. The error continued for this one user after changing this setting.
So now I'm left to brainstorm about what could be special about this one user's computer / software / internet connection that would hinder it from being able to connect to our SQL Server.
Our connection string does use our server's URL (not IP address), and I wondered if his laptop was having problems finding it by that address. However, he was able to access a website hosted from the same URL, so I guess the problem is somewhere else.
Any ideas would be greatly appreciated. Thanks!
You've probably long since solved this problem by now or moved on, but for those having similar problems with the Error 40/named pipes issue when connecting to a SQL server instance, the following simple solution worked for us:
You can force your client program to use TCP (or named pipes, or other available methods) by adding a prefix in your connection string.
For the .NET SQLConnection example, specify in the SQLConnection's connection string like so:
Server=tcp:192.168.0.1;Integrated Security=SSPI; database=sampledb
See this blog entry for more info.
Is it possible that they are being blocked by the hotel's firewall, which may only allow traffic on certain ports?
Here's what I've done:
I wrote a minimal web server (using Qt, but I don't think it's relevant here).
I'm running it on a legal Windows 7 32-bit.
The problem:
If I make a request with Firefox, IE, Chrome or Safari it takes takes about one second before my server sees that there is a new connection to be accepted.
Clues:
Using other clients (wget, own test client that just opens a socket) than Firefox, IE, Chrome, Safari seeing the new connection is matter of milliseconds.
I installed Apache and tried the clients mentioned above. Serving the request takes ~50ms as expected.
The problem isn't reproducible when running Windows XP (or compiling and running the same code under Linux)
The problem seems to present itself only when connecting to localhost. A friend connected over the Internet and serving the connection was a matter of milliseconds.
Running the server in different ports has no effect on the 1 second latency
Here's what I've tried without luck:
Stopped the Windows Defender service
Stopped the Windows Firewall service
Any ideas? Is this some clever 'security feature' in Windows 7? Why isn't Apache affected? Why are only the browsers affected?
If you're saying "localhost" instead of "127.0.0.1", you're forcing a name lookup before the actual connection attempt, adding delay.
In addition, some browsers, like Firefox 3.5+, don't use the operating system's DNS lookup mechanism, which is why it can have different performance than, say, wget.
You may be running into some automatic proxy discovery problem. In Firefox, you can disable this in Options | Advanced | Network | Settings; select either "No proxy" or give it explicit values. There's also the Internet Properties control panel, which is IE's network settings, but other browsers on Windows may obey settings here, too. Again, disable auto-proxy discovery. This can speed connections outside localhost, too.
For some reason Windows 7 takes 1 second to resolve address localhost regardless of it being in hosts file.
Adding localhost1 to hosts file and using that works around the problem.
When connecting to localhost on a IPv4/IPv6 dual stack host:
A DNS lookup is performed for localhost.
The DNS server (whether IPv6 enabled or not - this doesn't matter) returns both the AAAA record ::1, and the A record 127.0.0.1.
The client first attempts to connect to ::1.
We assume your server program is not IPv6-capable, which is a common case - due to historical reasons, many servers bind their socket to 0.0.0.0 by default rather than [::].
Here an ECONNREFUSED error would be raised for the client. This happens immediately on most platforms; on Windows however, a single call to connect() would try 3 times in 500ms intervals before giving up, hence taking a bit more than one second (See http://stackoverflow.com/q/19440364 for more details).
The client then creates a connection to 127.0.0.1 instead.
This would explain all your clues above:
If you make a request with Firefox, IE, Chrome, Safari or any other IPv6-capable clients, it takes takes about one second trying for ::1 before connecting to 127.0.0.1.
Your own test client just opens a INET socket, so it won't try ::1 at all.
Using a dual-stack server such as Apache, the clients will connect to ::1 happily.
The problem isn't reproducible on Windows XP, of which IPv6 support is not enabled by default.
The problem seems to present itself only when connecting to localhost, as your friend connected with an IPv4-only network.
Running the server in different ports has no effect on the 1 second latency.