How to configure a Custom Route in Azure

Configuring a custom route in Azure involves creating a User-Defined Route (UDR) in a route table and associating it with a subnet.

Follow these steps to implement a custom route in Azure:

Step 1: Create a Route Table

1. Navigate to the Azure Portal:

2. Search for Route Tables:

   • Use the search bar to find and select Route tables.

3. Create a New Route Table:

   • Click + Create.

   • Fill in the required details:

     • Name: Provide a unique name for the route table.

     • Subscription: Select the appropriate Azure subscription.

     • Resource Group: Choose or create a resource group.

     • Region: Match the region of your VNet.

   • Click Review + Create → Create.

Step 2: Add a Custom Route

1. After the route table is created, open it from the Route tables menu.

2. Add Routes:

   • Navigate to the Routes section and click + Add.

   • Enter the following details for your custom route:

     • Route name: A descriptive name (e.g., RouteToFirewall).

     • Address prefix: Specify the destination IP range or CIDR (e.g., 192.168.1.0/24).

     • Next hop type: Choose the next hop for the route:

       • Virtual appliance: Use for directing traffic through a firewall or NVA. Provide its private IP as the next hop.

       • Virtual network gateway: Use for routing traffic to on-premises networks via a VPN or ExpressRoute.

       • Internet: Use for forwarding traffic to the internet.

       • None: Use to block traffic to the specified address prefix.

     • Next hop address: If applicable, enter the IP address of the next hop (e.g., an NVA private IP).

   • Click OK to save.

Step 3: Associate the Route Table with a Subnet

1. In the created route table, go to the Subnets section.

2. Associate Subnet:

   • Click + Associate.

   • Select:

     • Virtual Network: Choose the VNet where the route table will apply.

     • Subnet: Pick the specific subnet to associate with the route table.

   • Click OK.

Step 4: Verify the Configuration

1. Deploy VMs:

   • Deploy VMs in the subnet associated with the route table.

2. Check Effective Routes:

   • Go to the Network Interface of a VM in the associated subnet.

   • Navigate to Effective routes to confirm the custom route is applied.

3. Test Connectivity:

   • Use tools like ping, traceroute, or tracert to validate traffic flow as per the custom route.

Example Use Case: Routing Traffic Through a Firewall (NVA)

Scenario

You want all traffic destined for 192.168.0.0/16 to go through a firewall (NVA) at 10.0.2.4.

• Route Name: RouteToFirewall

• Address Prefix: 192.168.0.0/16

• Next Hop Type: Virtual appliance

• Next Hop Address: 10.0.2.4

Tips and Best Practices

1. Subnet-Specific Routing

Apply custom routes only to required subnets to minimize unnecessary complexity.

2. High Availability

If using an NVA, ensure it is in an availability set or zone for reliability.

3. Testing

Test the routes in a staging or development environment before applying to production.

4. Documentation

Maintain documentation of custom routes for easier management and troubleshooting.

Summary

By following these steps, you can successfully configure custom routes to control traffic flow in Azure.