UDP networking on Azure VM

Question

I'm trying to create a UDP server on an Azure VM and a UDP client on my personal laptop using python. The server (on the VM) has bound a socket with local IP 127.0.0.1 and port 20001. I only have an NSG and no Vnet. The UDP client on my local laptop tries to send a message to the public IP of the VM on the same port 20001. However, the VM never receives this packet. I suspect it has something to do the networking and NSG settings but I'm a bit clueless as to what IPs and ports need to be whitelisted and where.
I tried :

• Changing the local IP on the server to 0.0.0.0.
• whitelisted my laptop IP and all ports on the NSG.

Is there something specific I need to whitelist on my laptop itself? Anything more to be whitelisted on the NSG?

Answer 1

anonymous user Thank you for reaching out to Microsoft Q&A.

I understand that you are unable to reach your Server VM on UDP port 20001. Please make sure to check the Effective security rules view in Azure Network Watcher on the NIC of the VM to verify the effective rules. You should ideally have the following rule:

Priority: Lowest priority than all rules (preferrably)
Source: Your client/laptop IP as seen from https://whatismyipaddress.com/
Source ports: 0-65535
Destination: 0.0.0.0/0
Destination Port/s: 20001 (either any port or 20001 port specifcially should work)
Protocol: UDP (or any)
Access: Allow

If possible, please share a snapshot of these Effective security rules for your NIC of the Virtual Machine so I can verify the same. Sharing details on how to get to the same in the portal below:

Further, please also make use of the IP flow verify option of networj watcher to check for the IP flow and determine if the access is allowed or not as shown from a test on my VM below:

I hope these tools help you troubleshoot the issue with your VM. If you need any further assistance, please feel free to let us know and we will be glad to assist further. Thank you!

Answer 2

Thank @SaiKishor-MSFT for replying. I tried as you mentioned and none of the settings worked. At the end I eventually opened up all ports and all IPs and checked that the flow was fine on the IP flow verify. But still the messages from my laptop UPD sender were not reaching the VM UDP listener. My VM was given a public IP of 20.193.236.121 and private ip of 10.0.0.4. My listener code import socket localIP = "0.0.0.0" localPort = 20001 bufferSize = 1024 msgFromServer = "Hello UDP Client" bytesToSend = str.encode(msgFromServer) # Create a datagram socket UDPServerSocket = socket.socket(family=socket.AF_INET, type=socket.SOCK_DGRAM) # Bind to address and ip UDPServerSocket.bind((localIP, localPort)) print("UDP server up and listening") # Listen for incoming datagrams while(True): bytesAddressPair = UDPServerSocket.recvfrom(bufferSize) message = bytesAddressPair[0] address = bytesAddressPair[1] clientMsg = "Message from Client:{}".format(message) clientIP = "Client IP Address:{}".format(address) print(clientMsg) print(clientIP) # Sending a reply to client UDPServerSocket.sendto(bytesToSend, address) My sender code import socket msgFromClient = "Hello UDP Server" bytesToSend = str.encode(msgFromClient) serverAddressPort = ("20.193.236.121", 20001) # I tried changing this to 10.0.0.4 as well but no success bufferSize = 1024 print("starting send") # Create a UDP socket at client side UDPClientSocket = socket.socket(family=socket.AF_INET, type=socket.SOCK_DGRAM) # Send to server using created UDP socket UDPClientSocket.sendto(bytesToSend, serverAddressPort) msgFromServer = UDPClientSocket.recvfrom(bufferSize) msg = "Message from Server {}".format(msgFromServer[0]) print(msg) ![115564-pic1.jpg][1] [1]: /api/attachments/115564-pic1.jpg?platform=QnA