It has been a really, really long time since I have written a blog post. This blog post talks about a recent problem which I encountered, forgot to write about on how I solved it and it bit me back again after some time! Reminder to all of you who are able to solve issues but don't document them!
One fine day, I start debugging an Azure Functions project by starting the Azure Storage Emulator and I am greeted with this -
PS C:\Program Files (x86)\Microsoft SDKs\Azure\Storage Emulator> .\AzureStorageEmulator.exe start -inprocess Windows Azure Storage Emulator 188.8.131.52 command line tool Service Status: Blob http://127.0.0.1:10000/ False Access is denied Error: Unable to start the storage emulator. PS C:\Program Files (x86)\Microsoft SDKs\Azure\Storage Emulator>
This was pretty strange as I checked which process was trying to use this port using netstat and I didn't see any entries -
I then went ahead and tried starting the Azure Functions project and it also threw the same error that Port 7071 is blocked and access was denied to it. This was very weird because I didn't have any applications running on that port & I also tried running the application with Administrator privileges. I tried running the Azure Functions project using a different port as well but it was also blocked. I also tried running Apache using XAMPP on various ports. It worked on some and it failed with the same port access blocked message on the others.
After running the usual
netstat commands, I thought that maybe it could be the Windows Firewall which might have some issue and it decided to block those ports. I turned on Windows Firewall logging and I didn't see any blockings over there as well. I then turned towards Event Viewer to see if there is any exception which is being generated in the Administrative Logs.
To my surprise, I found the port blocking event being generated i.e. Event 15005 HttpEvent with the following message -
Unable to bind to the underlying transport for 127.0.0.1:10000. 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.
After searching around for quite a bit, I came across this Github link. This talks about the Dynamic Port range reservations which can be used by other services to block ports. I ran
netsh int ipv4 show dynamicport tcp and the following list popped -
PS D:\> netsh interface ipv4 show excludedportrange protocol=tcp Protocol tcp Port Exclusion Ranges Start Port End Port ---------- -------- 1542 1641 1742 1841 1842 1941 2280 2379 2557 2656 2682 2781 2782 2881 2882 2981 2982 3081 3082 3181 3182 3281 3282 3381 3390 3489 3490 3589 3590 3689 3690 3789 3790 3889 3990 4089 4090 4189 4243 4342 4343 4442 4443 4542 4843 4942 5043 5142 5143 5242 5243 5342 5443 5542 5943 6042 6143 6242 6243 6342 6343 6442 6543 6642 7143 7242 7343 7442 7443 7542 7543 7642 7743 7842 8443 8542 8643 8742 8743 8842 8843 8942 9043 9142 9143 9242 9243 9342 9343 9442 9443 9542 9543 9642 9643 9742 9743 9842 9848 9947 9948 10047 10048 10147 10148 10247 10248 10347 10348 10447 10448 10547 50000 50059 * * - Administered port exclusions.
As you can see, the port 10000 was in the range of ports blocked. I confirmed this theory by running Apache on the various ports. As expected, it turned out that if I tried running Apache on the ports which are in the list (& range) above, it failed. On ports other than that, it worked without any issue.
The solution which worked for me was to remove Hyper-V, reserve the port for Hyper-V and then re-enable it.
Disable hyper-v (which will required a couple of restarts).
Do note that disabling and removing Hyper-V will mean that all your Virtual Machines & other objects part of Hyper-V will be removed.
dism.exe /Online /Disable-Feature:Microsoft-Hyper-V
When you finish all the required restarts, reserve the port you want so hyper-v doesn't reserve it back
netsh int ipv4 add excludedportrange protocol=tcp startport=50051 numberofports=1
Re-Enable hyper-V (which will require a couple of restart)
dism.exe /Online /Enable-Feature:Microsoft-Hyper-V /All
After rebooting after the 3rd step, my system was back to normal and the above problems were resolved.