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Tutorial: Route network traffic with a route table using the Azure portal

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Azure routes traffic between all subnets within a virtual network, by default. You can create your own routes to override Azure's default routing. Custom routes are helpful when, for example, you want to route traffic between subnets through a network virtual appliance (NVA).

Diagram of Azure resources created in tutorial.

In this tutorial, you learn how to:

  • Create a virtual network and subnets
  • Create an NVA that routes traffic
  • Deploy virtual machines (VMs) into different subnets
  • Create a route table
  • Create a route
  • Associate a route table to a subnet
  • Route traffic from one subnet to another through an NVA

Prerequisites

Sign in to Azure

Sign in to the Azure portal.

Create a virtual network and an Azure Bastion host

The following procedure creates a virtual network with a resource subnet, an Azure Bastion subnet, and a Bastion host:

  1. In the portal, search for and select Virtual networks.

  2. On the Virtual networks page, select + Create.

  3. 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 for the name.
    Select OK.
    Instance details
    Name Enter vnet-1.
    Region Select East US 2.

    Screenshot of the Basics tab for creating a virtual network in the Azure portal.

  4. Select Next to proceed to the Security tab.

  5. In the Azure Bastion section, select Enable Bastion.

    Bastion uses your browser to connect to VMs in your virtual network over Secure Shell (SSH) or Remote Desktop Protocol (RDP) by using their private IP addresses. The VMs don't need public IP addresses, client software, or special configuration. For more information, see What is Azure Bastion?.

    Note

    Hourly pricing starts from the moment that Bastion is deployed, regardless of outbound data usage. For more information, see Pricing and SKUs. If you're deploying Bastion as part of a tutorial or test, we recommend that you delete this resource after you finish using it.

  6. In Azure Bastion, enter or select the following information:

    Setting Value
    Azure Bastion host name Enter bastion.
    Azure Bastion public IP address Select Create a public IP address.
    Enter public-ip-bastion in Name.
    Select OK.

    Screenshot of options for enabling an Azure Bastion host as part of creating a virtual network in the Azure portal.

  7. Select Next to proceed to the IP Addresses tab.

  8. In the address space box in Subnets, select the default subnet.

  9. In Edit subnet, enter or select the following information:

    Setting Value
    Subnet purpose Leave the default of Default.
    Name Enter subnet-1.
    IPv4
    IPv4 address range Leave the default of 10.0.0.0/16.
    Starting address Leave the default of 10.0.0.0.
    Size Leave the default of /24 (256 addresses).

    Screenshot of configuration details for a subnet.

  10. Select Save.

  11. Select Review + create at the bottom of the window. When validation passes, select Create.

Create subnets

A DMZ and Private subnet are needed for this tutorial. The DMZ subnet is where you deploy the NVA, and the Private subnet is where you deploy the virtual machines that you want to route traffic to. The subnet-1 is the subnet created in the previous steps. Use subnet-1 for the public virtual machine.

  1. In the search box at the top of the portal, enter Virtual network. Select Virtual networks in the search results.

  2. In Virtual networks, select vnet-1.

  3. In vnet-1, select Subnets from the Settings section.

  4. In the virtual network's subnet list, select + Subnet.

  5. In Add subnet, enter or select the following information:

    Setting Value
    Name Enter subnet-private.
    Subnet address range Enter 10.0.2.0/24.

    Screenshot of private subnet creation in virtual network.

  6. Select Save.

  7. Select + Subnet.

  8. In Add subnet, enter or select the following information:

    Setting Value
    Name Enter subnet-dmz.
    Subnet address range Enter 10.0.3.0/24.

    Screenshot of DMZ subnet creation in virtual network.

  9. Select Save.

Create an NVA virtual machine

Network virtual appliances (NVAs) are virtual machines that help with network functions, such as routing and firewall optimization. In this section, create an NVA using an Ubuntu 22.04 virtual machine.

  1. In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results.

  2. Select + Create then Azure virtual machine.

  3. In Create a virtual machine enter or select the following information in the Basics tab:

    Setting Value
    Project details
    Subscription Select your subscription.
    Resource group Select test-rg.
    Instance details
    Virtual machine name Enter vm-nva.
    Region Select (US) East US 2.
    Availability options Select No infrastructure redundancy required.
    Security type Select Standard.
    Image Select Ubuntu Server 22.04 LTS - x64 Gen2.
    VM architecture Leave the default of x64.
    Size Select a size.
    Administrator account
    Authentication type Select Password.
    Username Enter a username.
    Password Enter a password.
    Confirm password Reenter password.
    Inbound port rules
    Public inbound ports Select None.

  4. Select Next: Disks then Next: Networking.

  5. In the Networking tab, enter or select the following information:

    Setting Value
    Network interface
    Virtual network Select vnet-1.
    Subnet Select subnet-dmz (10.0.3.0/24).
    Public IP Select None.
    NIC network security group Select Advanced.
    Configure network security group Select Create new.
    In Name enter nsg-nva.
    Select OK.

  6. Leave the rest of the options at the defaults and select Review + create.

  7. Select Create.

Create public and private virtual machines

Create two virtual machines in the vnet-1 virtual network. One virtual machine is in the subnet-1 subnet, and the other virtual machine is in the subnet-private subnet. Use the same virtual machine image for both virtual machines.

Create public virtual machine

The public virtual machine is used to simulate a machine in the public internet. The public and private virtual machine are used to test the routing of network traffic through the NVA virtual machine.

  1. In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results.

  2. Select + Create then Azure virtual machine.

  3. In Create a virtual machine enter or select the following information in the Basics tab:

    Setting Value
    Project details
    Subscription Select your subscription.
    Resource group Select test-rg.
    Instance details
    Virtual machine name Enter vm-public.
    Region Select (US) East US 2.
    Availability options Select No infrastructure redundancy required.
    Security type Select Standard.
    Image Select Ubuntu Server 22.04 LTS - x64 Gen2.
    VM architecture Leave the default of x64.
    Size Select a size.
    Administrator account
    Authentication type Select Password.
    Username Enter a username.
    Password Enter a password.
    Confirm password Reenter password.
    Inbound port rules
    Public inbound ports Select None.

  4. Select Next: Disks then Next: Networking.

  5. In the Networking tab, enter or select the following information:

    Setting Value
    Network interface
    Virtual network Select vnet-1.
    Subnet Select subnet-1 (10.0.0.0/24).
    Public IP Select None.
    NIC network security group Select None.

  6. Leave the rest of the options at the defaults and select Review + create.

  7. Select Create.

Create private virtual machine

  1. In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results.

  2. Select + Create then Azure virtual machine.

  3. In Create a virtual machine enter or select the following information in the Basics tab:

    Setting Value
    Project details
    Subscription Select your subscription.
    Resource group Select test-rg.
    Instance details
    Virtual machine name Enter vm-private.
    Region Select (US) East US 2.
    Availability options Select No infrastructure redundancy required.
    Security type Select Standard.
    Image Select Ubuntu Server 22.04 LTS - x64 Gen2.
    VM architecture Leave the default of x64.
    Size Select a size.
    Administrator account
    Authentication type Select Password.
    Username Enter a username.
    Password Enter a password.
    Confirm password Reenter password.
    Inbound port rules
    Public inbound ports Select None.

  4. Select Next: Disks then Next: Networking.

  5. In the Networking tab, enter or select the following information:

    Setting Value
    Network interface
    Virtual network Select vnet-1.
    Subnet Select subnet-private (10.0.2.0/24).
    Public IP Select None.
    NIC network security group Select None.

  6. Leave the rest of the options at the defaults and select Review + create.

  7. Select Create.

Enable IP forwarding

To route traffic through the NVA, turn on IP forwarding in Azure and in the operating system of vm-nva. When IP forwarding is enabled, any traffic received by vm-nva that's destined for a different IP address, isn't dropped and is forwarded to the correct destination.

Enable IP forwarding in Azure

In this section, you turn on IP forwarding for the network interface of the vm-nva virtual machine.

  1. In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results.

  2. In Virtual machines, select vm-nva.

  3. In vm-nva, select Networking from the Settings section.

  4. Select the name of the interface next to Network Interface:. The name begins with vm-nva and has a random number assigned to the interface. The name of the interface in this example is vm-nva124.

    Screenshot of network interface of NVA virtual machine.

  5. In the network interface overview page, select IP configurations from the Settings section.

  6. In IP configurations, select the box next to Enable IP forwarding.

    Screenshot of enablement of IP forwarding.

  7. Select Apply.

Enable IP forwarding in the operating system

In this section, turn on IP forwarding for the operating system of the vm-nva virtual machine to forward network traffic. Use the Azure Bastion service to connect to the vm-nva virtual machine.

  1. In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results.

  2. In Virtual machines, select vm-nva.

  3. Select Bastion in the Operations section.

  4. Enter the username and password you entered when the virtual machine was created.

  5. Select Connect.

  6. Enter the following information at the prompt of the virtual machine to enable IP forwarding:

    sudo vim /etc/sysctl.conf

  7. In the Vim editor, remove the # from the line net.ipv4.ip_forward=1:

    Press the Insert key.

    # Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1

    Press the Esc key.

    Enter :wq and press Enter.

  8. Close the Bastion session.

  9. Restart the virtual machine.

Create a route table

In this section, create a route table to define the route of the traffic through the NVA virtual machine. The route table is associated to the subnet-1 subnet where the vm-public virtual machine is deployed.

  1. In the search box at the top of the portal, enter Route table. Select Route tables in the search results.

  2. Select + Create.

  3. In Create Route table enter or select the following information:

    Setting Value
    Project details
    Subscription Select your subscription.
    Resource group Select test-rg.
    Instance details
    Region Select East US 2.
    Name Enter route-table-public.
    Propagate gateway routes Leave the default of Yes.

  4. Select Review + create.

  5. Select Create.

Create a route

In this section, create a route in the route table that you created in the previous steps.

  1. In the search box at the top of the portal, enter Route table. Select Route tables in the search results.

  2. Select route-table-public.

  3. In Settings select Routes.

  4. Select + Add in Routes.

  5. Enter or select the following information in Add route:

    Setting Value
    Route name Enter to-private-subnet.
    Destination type Select IP Addresses.
    Destination IP addresses/CIDR ranges Enter 10.0.2.0/24.
    Next hop type Select Virtual appliance.
    Next hop address Enter 10.0.3.4.
    This is the IP address you of vm-nva you created in the earlier steps..

    Screenshot of route creation in route table.

  6. Select Add.

  7. Select Subnets in Settings.

  8. Select + Associate.

  9. Enter or select the following information in Associate subnet:

    Setting Value
    Virtual network Select vnet-1 (test-rg).
    Subnet Select subnet-1.

  10. Select OK.

Test the routing of network traffic

Test routing of network traffic from vm-public to vm-private. Test routing of network traffic from vm-private to vm-public.

Test network traffic from vm-public to vm-private

  1. In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results.

  2. In Virtual machines, select vm-public.

  3. Select Bastion in the Operations section.

  4. Enter the username and password you entered when the virtual machine was created.

  5. Select Connect.

  6. In the prompt, enter the following command to trace the routing of network traffic from vm-public to vm-private:

    tracepath vm-private

    The response is similar to the following example:

    azureuser@vm-public:~$ tracepath vm-private
 1?: [LOCALHOST]                      pmtu 1500
 1:  vm-nva.internal.cloudapp.net                          1.766ms 
 1:  vm-nva.internal.cloudapp.net                          1.259ms 
 2:  vm-private.internal.cloudapp.net                      2.202ms reached
 Resume: pmtu 1500 hops 2 back 1

    You can see that there are two hops in the above response for tracepath ICMP traffic from vm-public to vm-private. The first hop is vm-nva. The second hop is the destination vm-private.

    Azure sent the traffic from subnet-1 through the NVA and not directly to subnet-private because you previously added the to-private-subnet route to route-table-public and associated it to subnet-1.

  7. Close the Bastion session.

Test network traffic from vm-private to vm-public

  1. In the search box at the top of the portal, enter Virtual machine. Select Virtual machines in the search results.

  2. In Virtual machines, select vm-private.

  3. Select Bastion in the Operations section.

  4. Enter the username and password you entered when the virtual machine was created.

  5. Select Connect.

  6. In the prompt, enter the following command to trace the routing of network traffic from vm-private to vm-public:

    tracepath vm-public

    The response is similar to the following example:

    azureuser@vm-private:~$ tracepath vm-public
 1?: [LOCALHOST]                      pmtu 1500
 1:  vm-public.internal.cloudapp.net                       2.584ms reached
 1:  vm-public.internal.cloudapp.net                       2.147ms reached
 Resume: pmtu 1500 hops 1 back 2

    You can see that there's one hop in the above response, which is the destination vm-public.

    Azure sent the traffic directly from subnet-private to subnet-1. By default, Azure routes traffic directly between subnets.

  7. Close the Bastion session.

Clean up resources

When you finish using the resources that you created, you can delete the resource group and all its resources:

  1. In the Azure portal, search for and select Resource groups.

  2. On the Resource groups page, select the test-rg resource group.

  3. On the test-rg page, select Delete resource group.

  4. Enter test-rg in Enter resource group name to confirm deletion, and then select Delete.

Next steps

In this tutorial, you:

  • Created a route table and associated it to a subnet.

  • Created a simple NVA that routed traffic from a public subnet to a private subnet.

You can deploy different preconfigured NVAs from the Azure Marketplace, which provide many useful network functions.

To learn more about routing, see Routing overview and Manage a route table.

To learn how to restrict network access to PaaS resources with virtual network service endpoints, advance to the next tutorial.

Restrict network access using service endpoints