ASP NET 5 MVC unable to connect to web server IIS Express

Question

What I m doing    Opening Visual Studio Community 2015 File -  New -  Project Under Visual C   Web -  ASP NET Web Application Web Application And press f5 for the popup error  unable to connect to web server  IIS Express      Deleting applicationhost config  located in Documents IISExpress config  doesn t change the error message   There s also an IISExpress folder in program files and program files  x86     Something I noticed  and I don t know if it s a problem       Referenced file  lib jquery-validation jquery validate js  not found    I got a dump with rawcap but I don t notice much in there  Some of what was there       Framework    FrameworkName   DNXCore Version v5 0   FriendlyName   DNX Core 5 0   ShortName   dnxcore50   RedistListPath  null    I don t notice a problem  but I have the network data if that can help figure out why I cannot connect to the web server  I get a RST ACK immediately so I m guessing the port is closed and whatever this web server is  isn t being setup   More on this problem  800700c1 error from  trace error  I ve tried    deleting applicationhost config  and changing port number  running visual studio as administrator deleting IISExpress folder in Documents  changes error message until the folder is reinstalled  toggling ssl off and on  copying url to launch box   note  I m not using ssl  clearing all sfc  scannow errors starting iisexpress with x86 version and 64-bit version

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TO CLARIFY  Really a lot of answers here are the same and say something like  Restart and it magically works again    Well  9 out of 10 times people have this issue like the OP it is because THE IP-ADDRESS IS ALREADY IN USE   ANSWER  There could be 2 ip-addresses that are in use  Both of them you can find by   1  Right-clicking on the start-up project  2  Click on  Properties   3  Click on the  Debug  tab  Here you see your  App URL  and your  SSL URL     If your  App URL  is in use  just change it there and save it and it should work again  If your  SSL URL  is in use  close down VS  delete the  applicationhost config  file in the hidden  vs folder of your project and open VS up again

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If you can afford to restart your machine then do it  this fixed my issue after almost an hour of trying to fix this issue with no hope

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I faced this issue in  net core 2 0 when I update my project s port number   I was able to sort out issue in two steps      STEP 1   DELETE  vs folder which is hidden inside main solution folder   close visual studio before this  then when you start again visual studio  this folder and file  applicationhost config  inside it will automatically create by visual studio  STEP 2   For multiple startup projects  if you are still facing issue then one by one run project as startup  and then run as multiple startup project

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I just Cleaned my solution  Then Re-Built it and finally hit F5 and it worked  So simple

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In my case this error was caused because I was running Docker   Make sure the port you are trying to host on is not in a Port Exclusion Range by running the following command in cmd powershell session   netsh interface ipv4 show excludedportrange protocol tcp   I tracked this down after reading through this stackoverflow question   Unable to launch the IIS Express Web server  Failed to register URL  Access is denied  Steve

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For me it was very easy   Clean the solution Re-build the solution  Run it Ctrl   F5  Run without Debugging

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With the Visual Studio closed  I deleted the temporary folder iisexpress in  C  Users  lt your user gt  AppData Local Temp iisexpress

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Try using a different port  I just set up a new Core 1 0 RC1 project and got the same error    Right click web project Debug tab Toggle Enable SSL off and on again  it should generate a new random port Copy the SSL URL and paste into Launch URL box Run the project   Worked for me  TM    Answer from  https   stackoverflow com a 28650554 134761

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I won t pretend to fully understand what MS bug creates this problem  but here is another potential solution   In the  vs config applicationHost config file  find the section for  lt system applicationHost gt  lt applicationPools gt   Under the pools  ensure that the managedRuntimeVersion attribute value matches the value which is in the IIS config for the system  and or the version of the  NET framework which is installed    For example  you may find  as I did  that the generated file has        lt add name  Clr4IntegratedAppPool  managedRuntimeVersion  v4 0  managedPipelineMode  Integrated  CLRConfigFile   IIS USER HOME  config aspnet config  autoStart  true    gt    In my case  you would replace this with        lt add name  Clr4IntegratedAppPool  managedRuntimeVersion  v4 0 30319  managedPipelineMode  Integrated  CLRConfigFile   IIS USER HOME  config aspnet config  autoStart  true    gt    Note the replacement from  v4 0  to  v4 0 30319   This resolved the issue     What appears to be going on   I believe that VS is generating an applicationHost config file with  default  versions for the  NET framework  which may not match the specific version which is installed configured on the system  You can debug observe this issue by tracing the execution in Process Monitor  and finding the command line for iisexpress exe  Running this command with  trace error added yields a more informative message about a failure to preload the CLR with version v4 0  To wit      Starting IIS Express       Failed while trying to preload CLR version v4 0   hr   80131700   Failed to initalize the W3WP HOST  hr   80131700   Process Model Shutdown called   Unable to start iisexpress      Anyway  figured this might be helpful to someone else  since it s common enough to have multiple references online with bad information  and I ve personally hit it a few times now

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I didn t figure out what was causing the issue  But a repair install fixed it

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Sign in as Administrator on local machine Open visual studio As Administrator Delete bin folders and  vs in project folder Delete all files in  users  Documents IISExpress   I think the underlying issue is permission for me

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I just encountered the same problem and I killed all the  iisexpress exe  processes that were still running  That worked for me

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In my case  I had to open up   Documents IISExpress config   folder and rename or delete existing config files  After this step  I ran the application and IISExpress generated new config files and the error was gone

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I just changed my profile from  IIS Express  to  MyProjectName   which I think is using kestrel as the http server instead of IIS  and now it s working fine

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For those who still experiencing the problem  I had the same issue but the message was showing IIS only not IIS Express  Try to start VS as administrator  That solved the issue for me

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After installing Update 2 for Visual Studio 2015 I started getting the same error  I tried everything above with no luck  However  I found a solution that works for me   Delete YourSolutionFolder   vs config applicationhost config file  note   vs is a hidden folder  Open Visual Studio  right-click on web site  gt  Properties  gt  Debug tab  gt  Web Server Settings  gt  App URL - change port number

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Try this first if it was working and suddenly stopped    Close Visual Studio Kill iisexpress exe processes Reopen Visual Studio

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And yet another way to get the same error   Using 0 0 0 0 as the IP address  That works fine in production  but has started failing on IIS Express for us  Changing that back to localhost in dev  solved our issue

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For me  IIS Express was not accessible when I added iplisten on DOS Prompt like this  netsh http add iplisten MyIPAddress  I fixed it by deleting the iplisten like this  netsh http delete iplisten MyIPAddress

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Mine happens as soon as I add a new binding inside the applicationhost config  running as administrator fixed the problem

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Windows 10 Defender Firewall was blocking it  I turned it off  ran the mvc core 2 0 application  and it worked  I then turned windows firewall on again and it remained working  All the other solutions although well intended didn t work for me  Hope this helps someone out there

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Restart your computer  that will work  at least it did it for me

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I repaired Visual Studio 2017 installation and it worked again

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In my case that was some other application listening on the same port which IIS Express trying to attach to  I have to run netstat -ao to see PID of process which is use same port and shutdown application  In my case application was Viber

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In my case  using ASP NET Core 3 1 and Visual Studio Professional 2019   I ve seen this twice and in both cases fixing it was as simple as rebooting my PC   I strongly suspect  but can t prove  that this could also be accomplished by restarting only a specific process  like in  Codenova s answer

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I had the same issue  i was able to solve it by changing the Port number    Right click on the project and select properties Go to the Debug section Under Web Server Settings change App URL port  just increase by one

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in my case it was pulse secure vpn tripping up Visual Studio 2019 community edition for some reason   workaround is to suspend vpn  start debug solution  then resume vpn connection

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I have solved it in a very simple way   By the following    Turn off Microsoft Visual Studio  Reopen it with  Run as administrator    Hope this helps you

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Faced the issue when reinstalled Windows on C  Drive  but my Visual Studio projects were intact on E  drive after the installation  I have resolved the issue by removing  vs folder in the visual studio project folder

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First  remove  vs folder from project  aside  sln file   then open project  Good luck

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I was able to toggle this error by changing a single thing  In my ASP Net Core 1 0 RC2 Web Application project s launchSettings json file      iisSettings          windowsAuthentication   false       anonymousAuthentication   true       iisExpress            applicationUrl    https   localhost 18177           sslPort   0              to      iisSettings          windowsAuthentication   false       anonymousAuthentication   true       iisExpress            applicationUrl    http   localhost 18177           sslPort   0              I had changed to https in an attempt to run the project using that protocol  Apparently this is not the place to make that change  I suspect it is creating multiple bindings on the same port  and IIS Express doesn t like that

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I had this issue on  net core 2 1  visual studio version 15 9 6  When i deleted the  vs folder  i reopened visual studio and the problem was still there  The solution that worked for me below    Delete  vs folder  it is a hidden folder   Restart Computer    Other Solutions    Close Visual Studio  delete bin and obj folders from the project folder  Open Project then rebuild solution  Try running Visual Studio as Administrator  Clean Solution then rebuild 1  Clean Solution  2  Exit Visual Studio  3  delete  vs folder 4  Re-open Visual Studio

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My solution  for  net core 2 0  was that i had forgot to add the port number in the applicationUrl  under iisExpress in launchSettings json   iisExpress        applicationUrl    https   localhost 50770      sslPort   50770

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Just run the visual studio as administrator and that s it

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I was trying to launch the app on the URL  quot http   192 168 0 1 4000  quot   and the above answers didn t help  Finally  I added the   4000 localhost HTTP binding to the  vs     applicationhost config  so now the binding section looks like this   lt bindings gt     lt binding protocol  quot http quot  bindingInformation  quot   4000 localhost quot    gt     lt binding protocol  quot http quot  bindingInformation  quot   4000 192 168 0 1 quot    gt   lt  bindings gt   And it did the trick

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Exit VS and delete the  project   vs applicationhost config file  Restart VS  It should start working

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I ve tried all listed here  but nothing really helped  Solution was simply to change IIS server port listening  apparantely port 80 was already taken  but the error message didn t said so   Btw  in my case port 80 was taken by main windows service which I couldn t stop kill    From main ISS manager  go to Default Web Site and edit bindings  below screenshot is in Polish - hope it helps anyway   Then I ve changed port 80 from http binding to  whatever you like  8081 as below   So after that all projects web page  apis  started working correctly

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Run VisualStudio with administrator privilegies and run the project  Then close VisualStudio and all errors and run VisualStudio again with the normal user   This did it for me   Looks like that IIS has to write something to some config with admin privilegies  port 80 didn t work with normal user but port 6767 worked fine

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For the following   All I had to do was navigate to the current project solution directory    vs   config to delete applicationhost config  then restart VS and run as usual without problem    vs is a hidden folder

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The issue may be because  v  Enabled SSL was selected for your project  see the Debug tab in the project settings window   but Visual Studio decides to be dumb and setup something like http   localhost 32396   The reason it fails is because 1  it is not HTTPS  and 2  the cert is not valid  To force it  you need to use a port in the range 44300-44398   See https   stackoverflow com a 24957146 1236397

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For me  I had to kill  NET Core Host  in my background processes   Task Manager   Background Processes   Net Core Host   End Task  Then restarting the debug instance worked again as normal

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delete bin and obj folders from the project folder and rebuild

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For me the problem was that an other process was using the same port   In my case it was outlook that was using the same port as my site and thus my site couldn t start    Yes you can change the local port  but if you are running an API or something that other applications need  you don t always want to do this    To get a list of what applications are using what port open CMD and type  netstat -aon  You will get a list of ports  Find the port that your site should use  or that you want to use and write down   remember the PID   Now open task manager and click on the tab  details   Find the process with your PID and end it  Now you should be able to start IIS Express with that port

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Change port manually for http and https  or disable https

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I had this same issue  but the way I fixed it was by going to the applicationhost config and remove a port which was not added by me  IIS Express I would guess  which placed my specific port site on another port    Here is what the config file had for my bindings    lt bindings gt         lt binding protocol  http  bindingInformation    54764 localhost    gt         lt binding protocol  https  bindingInformation    44360 localhost    gt   lt  bindings gt    I removed the first bindings item as the only port I wanted was 44360  My config file now looks like this    lt bindings gt         lt binding protocol  https  bindingInformation    44360 localhost    gt   lt  bindings gt    Now I don t see the error when I debug   I also noticed my second API in my project had port 80 also assigned to it  I removed that as well

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As Svenmarim already stated  this mostly occurs because the ip adress is already in use  This answer and its comments from the visualstudio developer community pointed me to the right direction  In my case i was trying to access my local IISExpress instance from my local network and therefore binded my ip adress with the same port which uses my IISExpress instance via netsh http add urlacl url http   192 168 1 42 58938  user everyone After removing this binding via netsh http delete urlacl url http   192 168 1 42 58938  it worked again

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Just close the visual studio and reopen and execute  It worked for me

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I m using VS2017  I Disable Tool  gt  Options  gt  Debugging  gt  Enable JavaScript debugging for ASP NET then work

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For me  this started happening on a project that was working  but then one day I got this error  I tried all suggestions around the  vs folder  applicationhost config file  changing ports  restarting VS  rebooting Windows  reinstalling IIS Express  Nothing worked  I even created a new bare-bones web app  and got the same error  I have a feeling the IT department made some kind of change to my system   After I try to run the project and IIS Express has started  in my elevated cmd prompt I run netstat -ano  find  44312  where 44312 is the port number of my web application  I noticed what s returned is not the usual localhost IP  127 0 0 1   It was some external IP  It tells me IIS Express using a different IP   Then I ran netsh http show iplisten and I see that same IP in the results  netsh http delete iplisten  external ip   and BOOM  the web app loads

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If you have read till this point  then probably  none of the answers above worked for you or suites you    My solution to this problem is to shut down your computer  making sure to have saved all necessary open documents  Reboot your computer  Run Visual Studio and then you are good to go

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The solution that worked for me was to   Close the VS project In File Explorer  navigate to the project and delete the entire   vs  folder Restart the project Run as  Debug  Works Apparently  it has something to do with the  applicationhost config  file   Enjoy

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if you copy the project from other pc  you can try  netsh interface ipv4 show excludedportrange protocol tcp  to check the Start Port to End Port that is allowed to use on you computer

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For me  it was a mixture of following these instructions      Delete your web application   s  vs applicationhost config and try   again    And then  perhaps most importantly  running Visual Studio with admin privileges

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Just change all port numbers to new of any working series     Don t change application host  config

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Make sure the following registry key  HKEY LOCAL MACHINE SYSTEM CurrentControlSet Services HTTP Parameters ListenOnlyList does not contain IP addresses that are not bound to an enabled network adapter on your machine    This was the cause of my issue after attempting the various other solutions listed in this SO question and many others  such as    Deleting applicationhost config Toggling SSL on and off  Changing Port number  Manually killing IIS Express process  Reinstalling IIS Express  Repairing Visual Studio  Installing a new version of Visual Studio Creating a new  Net Framework Web Application  Creating a new  Net Core Web Application  Running netsh urlacl commands Running netsh http add iplisten ipaddress    Running Visual Studio as an administrator  Assuring bypass traversal rights where applied     Apparently  when IIS express was attempting to start it was trying to bind to this invalid IP  The fix was to delete the invalid IP  This additional invalid possibly came from my home wireless network while at work I am assigned a different IP via the hard wired adapter   A catch-all solution may be to delete all IPs out of the registry key and run netsh http add iplisten ipaddress    to allow listening on all addresses   I was able to track this issue down after noticing the following event log entries    IIS Express  The worker process for app pool  WebApplicationNetCore AppPool   PID  23260   failed to initialize the http sys communication when asked to start processing http requests and therefore will be considered ill by W3SVC and terminated   The data field contains the error number  IIS Express  The worker process failed to initialize correctly and therefore could not be started   The data is the error  HTTP Event  Unable to bind to the underlying transport for 192 168 1 42 52999   The IP Listen-Only list may contain a reference to an interface which may not exist on this machine   The data field contains the error number

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Copied my comment to an answer by request  For Net Core 2 2 project - After a MASSIVE struggle and trying everything from deleting  vs folder  deleting IIS Express configs  changing port numbers  changing bindings  and to running VS as admin I FINALLY fixed issue by  closing VS  deleting launchSettings json opening VS which re-generated launchSettings json   It was not apparent that the file was corrupt or incorrect or even when it changed to cause failure

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If you are using VS 2017 or VS 2019 with ASP Net Core  you can directly go to launchSettings json under Properties folder and just change the Port number of applicationUrl key  for iisSetting

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I was able to resolve this by restarting my computer   I tried a few things unsuccessfully and finally gave up and restarted my computer   It has been working well now for a couple of days after I restarted   Probably the result of some process that was hung

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I added  UseUrls  https   localhost  lt some port gt     to the Program cs   This seemed to do the trick for me

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If you don t want to reboot your can  a solution is to manually attach the debugger  In my case the application is launched but visual studio fails to connect to the iis  In Visual Studio 2019  Debug - gt  Attach to process - gt  filter by iis and select iisexpress exe

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I simply toggled on  Enable SSL   This solved my problem    Right click web project Debug tab Toggle Enable SSL  on   if it is off  which was my case

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Many of these answered don t fully address the issue at hand  The real problem for me was that I had two bindings using the same port in my applicationhost config file AND I hadn t opened up the port to my second  non localhost  binding  VS will allow you to still run under these circumstances but only if you are in admin mode  hence all of the answers above     You are essentially creating two IIS express instances of your app on the same port  so changing one of the ports in your applicationhost config file will allow you to proceed  There are two different applicationhost config files however  You will want to select the one that has the binding IP and port that you see in your project s properties      Go to the folder where you can see your project solution and project folders  show hidden items in File Explorer   Navigate into your hidden  vs folder -   YourAppName  folder -  config  It should contain the binding info you saw in your project s properties    Example    lt bindings gt       lt binding protocol  http  bindingInformation    7000 127 0 0 1    gt       lt binding protocol  http  bindingInformation    7000 192 168 0 5    gt   lt  bindings gt    Change one of those port numbers to something other than  7000  so that you aren t trying to use the same port   In my case  I m using a 192 address which is not a localhost address  so I need to use some netsh commands to open that port and ip up  Here is a Link that shows how to open up ports for IIS Express to allow remote connection  Running as a normal user will not work unless you run those netsh commands listed    Here are the netsh commands    netsh http add urlacl url http   192 168 1 42 58938  user everyone netsh advfirewall firewall add rule name  IISExpressWeb  dir in protocol tcp localport 58938 profile private remoteip localsubnet action allow   Copy those commands and run them in cmd with ADMIN privileges and with YOUR ip address and port number

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Try in cmd  taskkill  im iisexpress exe  f taskkill  im dotnet exe  f   and press f5  I do not change ports  delete files or reboot VS

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