Tutorial: Filter network traffic with a network security group using the Azure portal
Article
You can use a network security group to filter inbound and outbound network traffic to and from Azure resources in an Azure virtual network.
Network security groups contain security rules that filter network traffic by IP address, port, and protocol. When a network security group is associated with a subnet, security rules are applied to resources deployed in that subnet.
In this tutorial, you learn how to:
Create a network security group and security rules
Create application security groups
Create a virtual network and associate a network security group to a subnet
Deploy virtual machines and associate their network interfaces to the application security groups
If you choose to install and use PowerShell locally, this article requires the Azure PowerShell module version 1.0.0 or later. Run Get-Module -ListAvailable Az to find the installed version. If you need to upgrade, see Install Azure PowerShell module. If you're running PowerShell locally, you also need to run Connect-AzAccount -Environment AzureChinaCloud to create a connection with Azure.
If you don't have an Azure trail subscription, create a trial subscription before you begin.
You can use the local Azure CLI.
If you prefer, install the Azure CLI to run CLI reference commands.
Sign in to the Azure CLI by using the az login command. To finish the authentication process, follow the steps displayed in your terminal. For other sign-in options, see Sign in with the Azure CLI.
When you're prompted, install the Azure CLI extension on first use. For more information about extensions, see Use extensions with the Azure CLI.
Run az version to find the version and dependent libraries that are installed. To upgrade to the latest version, run az upgrade.
This article requires version 2.0.28 or later of the Azure CLI.
The following procedure creates a virtual network with a resource subnet.
In the portal, search for and select Virtual networks.
On the Virtual networks page, select + Create.
On the Basics tab of Create virtual network, enter or select the following information:
Setting
Value
Project details
Subscription
Select your subscription.
Resource group
Select Create new. Enter test-rg in Name. Select OK.
Instance details
Name
Enter vnet-1.
Region
Select (Asia Pacific) China East 2.
Select Next: IP Addresses to proceed to the IP Addresses tab.
In the address space box in Subnets, select the default subnet.
In Edit subnet, enter or select the following information:
Setting
Value
Subnet name
Enter subnet-1.
Subnet address range
Enter 10.0.0.0/24.
Select Save.
Select Review + create at the bottom of the screen, and when validation passes, select Create.
First create a resource group for all the resources created in this article with New-AzResourceGroup. The following example creates a resource group in the westus2 location:
Create a subnet configuration with New-AzVirtualNetworkSubnetConfig, and then write the subnet configuration to the virtual network with Set-AzVirtualNetwork. The following example adds a subnet named subnet-1 to the virtual network and associates the nsg-1 network security group to it:
First create a resource group for all the resources created in this article with az group create. The following example creates a resource group in the westus2 location:
az group create \
--name test-rg \
--location westus2
Create a virtual network with az network vnet create. The following example creates a virtual named vnet-1:
Add a subnet to a virtual network with az network vnet subnet create. The following example adds a subnet named subnet-1 to the virtual network and associates the nsg-1 network security group to it:
In the search box at the top of the portal, enter Application security group. Select Application security groups in the search results.
Select + Create.
On the Basics tab of Create an application security group, enter, or select this information:
Setting
Value
Project details
Subscription
Select your subscription.
Resource group
Select test-rg.
Instance details
Name
Enter asg-web.
Region
Select (Asia Pacific) China North 2.
Select Review + create.
Select + Create.
Repeat the previous steps, specifying the following values:
Setting
Value
Project details
Subscription
Select your subscription.
Resource group
Select test-rg.
Instance details
Name
Enter asg-mgmt.
Region
Select (Asia Pacific) China North 2.
Select Review + create.
Select Create.
Create an application security group with New-AzApplicationSecurityGroup. An application security group enables you to group servers with similar port filtering requirements. The following example creates two application security groups.
Create an application security group with az network asg create. An application security group enables you to group servers with similar port filtering requirements. The following example creates two application security groups.
In the search box at the top of the portal, enter Network security group. Select Network security groups in the search results.
Select nsg-1.
Select Subnets from the Settings section of nsg-1.
In the Subnets page, select + Associate:
Under Associate subnet, select vnet-1 (test-rg) for Virtual network.
Select subnet-1 for Subnet, and then select OK.
Use Get-AzVirtualNetwork to retrieve the virtual network object, and then use Set-AzVirtualNetworkSubnetConfig to associate the network security group with the subnet. The following example retrieves the virtual network object and updates the subnet configuration to associate the network security group:
# Retrieve the virtual network
$vnet = Get-AzVirtualNetwork -Name "vnet-1" -ResourceGroupName "test-rg"
# Update the subnet configuration to associate the network security group
$subnetConfigParams = @{
VirtualNetwork = $vnet
Name = "subnet-1"
AddressPrefix = $vnet.Subnets[0].AddressPrefix
NetworkSecurityGroup = Get-AzNetworkSecurityGroup -Name "nsg-1" -ResourceGroupName "test-rg"
}
Set-AzVirtualNetworkSubnetConfig @subnetConfigParams
# Update the virtual network with the new subnet configuration
$vnet | Set-AzVirtualNetwork
Use az network vnet subnet update to associate the network security group with the subnet. The following example associates the nsg-1 network security group with the subnet-1 subnet:
Select Inbound security rules from the Settings section of nsg-1.
In Inbound security rules page, select + Add.
Create a security rule that allows ports 80 and 443 to the asg-web application security group. In Add inbound security rule page, enter or select the following information:
Setting
Value
Source
Leave the default of Any.
Source port ranges
Leave the default of (*).
Destination
Select Application security group.
Destination application security groups
Select asg-web.
Service
Leave the default of Custom.
Destination port ranges
Enter 80,443.
Protocol
Select TCP.
Action
Leave the default of Allow.
Priority
Leave the default of 100.
Name
Enter allow-web-all.
Select Add.
Complete the previous steps with the following information:
Setting
Value
Source
Leave the default of Any.
Source port ranges
Leave the default of (*).
Destination
Select Application security group.
Destination application security group
Select asg-mgmt.
Service
Select RDP.
Action
Leave the default of Allow.
Priority
Leave the default of 110.
Name
Enter allow-rdp-all.
Select Add.
Caution
In this article, RDP (port 3389) is exposed to the internet for the VM that is assigned to the asg-mgmt application security group.
For production environments, instead of exposing port 3389 to the internet, it's recommended that you connect to Azure resources that you want to manage using a VPN, private network connection, or Azure Bastion.
Create a security rule with New-AzNetworkSecurityRuleConfig. The following example creates a rule that allows traffic inbound from the internet to the asg-web application security group over ports 80 and 443:
# Retrieve the existing network security group
$nsg = Get-AzNetworkSecurityGroup -Name "nsg-1" -ResourceGroupName "test-rg"
# Add the new rules to the security group
$nsg.SecurityRules += $webRule
$nsg.SecurityRules += $mgmtRule
# Update the network security group with the new rules
Set-AzNetworkSecurityGroup -NetworkSecurityGroup $nsg
Caution
In this article, RDP (port 3389) is exposed to the internet for the VM that is assigned to the asg-mgmt application security group.
For production environments, instead of exposing port 3389 to the internet, it's recommended that you connect to Azure resources that you want to manage using a VPN, private network connection, or Azure Bastion.
Create a security rule with az network nsg rule create. The following example creates a rule that allows traffic inbound from the internet to the asg-web application security group over ports 80 and 443:
In this article, SSH (port 22) is exposed to the internet for the VM that is assigned to the asg-mgmt application security group.
For production environments, instead of exposing port 22 to the internet, it's recommended that you connect to Azure resources that you want to manage using a VPN, private network connection, or Azure Bastion.
Create two network interfaces with New-AzNetworkInterface, and assign a public IP address to the network interface. The following example creates a network interface, associates the public-ip-vm-web public IP address to it.
Create two VMs in the virtual network so you can validate traffic filtering in a later step.
Create a VM configuration with New-AzVMConfig, then create the VM with New-AzVM. The following example creates a VM that serves as a web server. The -AsJob option creates the VM in the background, so you can continue to the next step:
The virtual machine takes a few minutes to create. Don't continue with the next step until Azure finishes creating the VM.
Create two VMs in the virtual network so you can validate traffic filtering in a later step.
Create a VM with az vm create. The following example creates a VM that serves as a web server. The --nsg "" option is specified to prevent Azure from creating a default network security group for the network interface Azure creates when it creates the VM. The command prompts you to create a password for the VM. SSH keys aren't used in this example to facilitate the later steps in this article. In a production environment, use SSH keys for security.
Create a VM with az vm create. The following example creates a VM that serves as a management server.
The following example creates a VM and adds a user account. The --generate-ssh-keys parameter causes the CLI to look for an available ssh key in ~/.ssh. If one is found, that key is used. If not, one is generated and stored in ~/.ssh. Finally, we deploy the latest Ubuntu 22.04 image.
When you created the VMs, Azure created a network interface for each VM, and attached it to the VM.
Add the network interface of each VM to one of the application security groups you created previously:
In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results, then select vm-web.
Select Application security groups from the Networking section of vm-web.
Select Add application security groups, then in the Add application security groups tab, select asg-web. Finally, select Add.
Repeat the previous steps for vm-mgmt, selecting asg-mgmt in the Add application security groups tab.
Use Get-AzNetworkInterface to retrieve the network interface of the virtual machine, and then use Get-AzApplicationSecurityGroup to retrieve the application security group. Finally, use Set-AzNetworkInterface to associate the application security group with the network interface. The following example associates the asg-web application security group with the vm-web-nic network interface:
Use az network nic update to associate the network interface with the application security group. The following example associates the asg-web application security group with the vm-web-nic network interface:
# Retrieve the network interface name associated with the virtual machine
nic_name=$(az vm show --resource-group test-rg --name vm-web --query 'networkProfile.networkInterfaces[0].id' -o tsv | xargs basename)
# Associate the application security group with the network interface
az network nic ip-config update \
--name ipconfigvm-web \
--nic-name $nic_name \
--resource-group test-rg \
--application-security-groups asg-web
Repeat the command to associate the asg-mgmt application security group with the vm-mgmt-nic network interface.
# Retrieve the network interface name associated with the virtual machine
nic_name=$(az vm show --resource-group test-rg --name vm-mgmt --query 'networkProfile.networkInterfaces[0].id' -o tsv | xargs basename)
# Associate the application security group with the network interface
az network nic ip-config update \
--name ipconfigvm-mgmt \
--nic-name $nic_name \
--resource-group test-rg \
--application-security-groups asg-mgmt
In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results.
Select vm-mgmt.
On the Overview page, select the Connect button and then select Native RDP.
Select Download RDP file.
Open the downloaded rdp file and select Connect. Enter the username and password you specified when creating the VM.
Select OK.
You might receive a certificate warning during the connection process. If you receive the warning, select Yes or Continue, to continue with the connection.
The connection succeeds, because inbound traffic from the internet to the asg-mgmt application security group is allowed through port 3389.
The network interface for vm-mgmt is associated with the asg-mgmt application security group and allows the connection.
Open a PowerShell session on vm-mgmt. Connect to vm-web using the following:
mstsc /v:vm-web
The RDP connection from vm-mgmt to vm-web succeeds because virtual machines in the same network can communicate with each other over any port by default.
You can't create an RDP connection to the vm-web virtual machine from the internet. The security rule for the asg-web prevents connections to port 3389 inbound from the internet. Inbound traffic from the Internet is denied to all resources by default.
To install Microsoft IIS on the vm-web virtual machine, enter the following command from a PowerShell session on the vm-web virtual machine:
After the IIS installation is complete, disconnect from the vm-web virtual machine, which leaves you in the vm-mgmt virtual machine remote desktop connection.
Disconnect from the vm-mgmt VM.
Search for vm-web in the portal search box.
On the Overview page of vm-web, note the Public IP address for your VM. The address shown in the following example is 203.0.113.103. Your address is different:
To confirm that you can access the vm-web web server from the internet, open an internet browser on your computer and browse to http://<public-ip-address-from-previous-step>.
You see the IIS default page, because inbound traffic from the internet to the asg-web application security group is allowed through port 80.
The network interface attached for vm-web is associated with the asg-web application security group and allows the connection.
Use Get-AzPublicIpAddress to return the public IP address of a VM. The following example returns the public IP address of the vm-mgmt VM:
Use the following command to create a remote desktop session with the vm-mgmt VM from your local computer.
mstsc /v:$publicIP
Enter the user name and password you specified when creating the VM (you might need to select More choices, then Use a different account, to specify the credentials you entered when you created the VM), then select OK. You might receive a certificate warning during the sign-in process. Select Yes to proceed with the connection.
The connection succeeds. Port 3389 is allowed inbound from the internet to the asg-mgmt application security group. The network interface attached to the vm-mgmt VM is in this group.
Use the following command to create a remote desktop connection to the vm-web VM, from the vm-mgmt VM, with the following command, from PowerShell:
mstsc /v:vm-web
The connection succeeds because a default security rule within each network security group allows traffic over all ports between all IP addresses within a virtual network. You can't create a remote desktop connection to the vm-web VM from the internet because the security rule for the asg-web doesn't allow port 3389 inbound from the internet.
Use the following command to install Microsoft IIS on the vm-web VM from PowerShell:
After the IIS installation is complete, disconnect from the vm-web VM, which leaves you in the vm-mgmt VM remote desktop connection. To view the IIS welcome screen, open an internet browser and browse to http://vm-web.
Disconnect from the vm-mgmt VM.
On your computer, enter the following command from PowerShell to retrieve the public IP address of the vm-web server:
To confirm that you can access the vm-web web server from outside of Azure, open an internet browser on your computer and browse to http://<public-ip-address-from-previous-step>. The connection succeeds. Port 80 is allowed inbound from the internet to the asg-web application security group. The network interface attached to the vm-web VM is in this group.
Using an SSH client of your choice, connect to the VMs created previously. For example, the following command can be used from a command line interface such as Windows Subsystem for Linux to create an SSH session with the vm-mgmt VM. You can sign-in to the virtual machines using your Microsoft Entra ID credentials or you can use the SSH key that you used to create the VMs. In the following example, we use the SSH key to sign in to management VM and then sign in to the web VM from the management VM with a password.
The connection succeeds because the network interface attached to the vm-mgmt VM is in the asg-mgmt application security group, which allows port 22 inbound from the Internet.
Use the following command to SSH to the vm-web VM from the vm-mgmt VM:
ssh -o StrictHostKeyChecking=no azureuser@vm-web
The connection succeeds because a default security rule within each network security group allows traffic over all ports between all IP addresses within a virtual network. You can't SSH to the vm-web VM from the Internet because the security rule for the asg-web doesn't allow port 22 inbound from the Internet.
Use the following commands to install the nginx web server on the vm-web VM:
The vm-web VM is allowed outbound to the Internet to retrieve nginx because a default security rule allows all outbound traffic to the Internet. Exit the vm-web SSH session, which leaves you at the username@vm-mgmt:~$ prompt of the vm-mgmt VM. To retrieve the nginx welcome screen from the vm-web VM, enter the following command:
curl vm-web
Sign out of the vm-mgmt VM. To confirm that you can access the vm-web web server from outside of Azure, enter curl <publicIpAddress> from your own computer. The connection succeeds because the asg-web application security group, which the network interface attached to the vm-web VM is in, allows port 80 inbound from the Internet.
Azure routes traffic between subnets by default. You might instead, choose to route traffic between subnets through a VM, serving as a firewall, for example.
To learn how to create a route table, advance to the next tutorial.