You buy a new Azure subscription, spin up an Azure Virtual Machine. Now you want to test if it is working or not. So, you pull up the infamous Command Prompt (or powershell) and Ping the VIP (Virtual/Public IP) of your Azure Virtual Machine. Wola!! The ping fails with 100% loss. But you can see that the Azure Portal shows that your virtual machine is up and running. To double check, you even RDP to your VM and it is all good. This is one of the many situations where the Azure new comers get confused. Let me break down this for you:-
The explanation for this behaviour is that the good old, Windows Ping.exe uses ICMP protocol to communicate. But the Azure Load Balancer does not support ICMP protocol when a connection is being made from external source to Azure. This means, your local computer will not be able to “Ping” (probing using Ping.exe) the Azure virtual Machines. However Azure Load Balancer allows ICMP protocol inside the azure (internally). This means, two Azure virtual machines are able to talk to each other.
The solution is to ping the port of your Virtual Machine.
Example: Ping xx.xx.xx.xx:1234
Since Ping.exe does not support probing the port, we have to use the other tools like PSPing, TCPPing etc, to achieve this.
This explains most of it. I am going to demonstrate whatever I just explained.
Below is the details of my virtual machine:
When I ping the VIP – 126.96.36.199, using the default Ping.exe. You can observe that we end up having 100% packet loss.
This behaviour is because the Azure Load Balancer does not allow ICMP communication between Azure and the external source. And Microsoft’s Ping.exe uses ICMP protocol.
The solution is to use PSPing (among many other options), and ping the port of the Virtual Machine. Please note that you have to add relevant entry in the NSG (Network Security Group) to allow incoming traffic to your Virtual Machine.
Since this is just a Demo, I have allowed all the traffic to my Virtual Machine via the port 3389. You have to use appropriate NSG and ACLs to your Virtual Machine and Subnet, in your production environment.
PSPing.exe comes with a bundle – PSTools. This toolset can be downloaded here.
Copy PsPing onto your executable path. Typing “psping” displays its usage syntax.
Note: If you are using the PSPing tool for the first time, you may have to agree to the terms and conditions before using it.
Since I have my port – 3389 opened for all incoming traffic. I will go ahead and use the PSPing tool to ping the port from my local computer. And as you can see it works like a charm !!
Finally, note that you can ping only to the port for which you have enabled the incoming traffic. Since I have not enabled port 80, I expect the packets to be dropped.