You open a port, or create an endpoint, to a virtual machine (VM) in Azure by creating a network filter on a subnet or VM network interface. You place these filters, which control both inbound and outbound traffic, on a Network Security Group attached to the resource that receives the traffic.
Let's use a common example of web traffic on port 80. Once you have a VM that is configured to serve web requests on the standard TCP port 80 (remember to start the appropriate services and open any OS firewall rules on the VM as well), you:
- Create a Network Security Group.
- Create an inbound rule allowing traffic with:
- the destination port range of "80"
- the source port range of "*" (allowing any source port)
- a priority value of less 65,500 (to be higher in priority than the default catch-all deny inbound rule)
- Associate the Network Security Group with the VM network interface or subnet.
You can create complex network configurations to secure your environment using Network Security Groups and rules. Our example uses only one or two rules that allow HTTP traffic or remote management. For more information, see the following 'More Information' section or What is a Network Security Group?
You can also perform these steps using Azure PowerShell.
First, create your Network Security Group. Select a resource group in the portal, click Add, then search for and select 'Network security group':
Enter a name for your Network Security Group, select or create a resource group, and select a location. Click Create when finished:
Select your new Network Security Group. Select 'Inbound security rules', then click the Add button to create a rule:
Provide a name for your new rule. Port 80 is already entered by default. This blade is where you would change the source, protocol, and destination when adding additional rules to your Network Security Group. Click OK to create the rule:
Your final step is to associate your Network Security Group with a subnet or a specific network interface. Let's associate the Network Security Group with a subnet. Select 'Subnets', then click Associate:
Select your virtual network, and then select the appropriate subnet:
You have now created a Network Security Group, created an inbound rule that allows traffic on port 80, and associated it with a subnet. Any VMs you connect to that subnet are reachable on port 80.
More information on Network Security Groups
The quick commands here allow you to get up and running with traffic flowing to your VM. Network Security Groups provide many great features and granularity for controlling access to your resources. You can read more about creating a Network Security Group and ACL rules here.
You can define Network Security Groups and ACL rules as part of Azure Resource Manager templates. Read more about creating Network Security Groups with templates.
If you need to use port-forwarding to map a unique external port to an internal port on your VM, use a load balancer and Network Address Translation (NAT) rules. For example, you may want to expose TCP port 8080 externally and have traffic directed to TCP port 80 on a VM. You can learn about creating an Internet-facing load balancer.
In this example, you created a simple rule to allow HTTP traffic. You can find information on creating more detailed environments in the following articles: