Learn about System Routes in Azure

In Azure, system routes are the default routes automatically created by Azure in the route table of a virtual network (VNet).

These routes control the flow of traffic between resources in the VNet, across connected VNets, and to external networks like the internet.

They ensure connectivity and manage routing without requiring user configuration.

Key Features of System Routes:

1. Default Connectivity

• Enable communication between resources in the same VNet (intra-VNet traffic).

• Support communication between VNets connected via VNet peering.

• Allow traffic to the internet for resources with a public IP or a default outbound connection.

2. Automatic Management

• Azure automatically creates and updates system routes when you set up VNets, subnets, and network connections.

3. Cannot Be Deleted

• System routes are built into the platform and cannot be removed, but their behavior can be overridden using user-defined routes (UDRs).

Common System Routes:

1. Local VNet Route

• Destination: The VNet's address space.

• Next hop: Local.

• Enables communication between resources within the VNet.

2. Internet Route

• Destination: 0.0.0.0/0 (default route).

• Next hop: Internet.

• Allows outbound internet access for resources with a public IP or NAT configuration.

3. VNet Peering Route

• Destination: Address space of a peered VNet.

• Next hop: VNet peering.

• Handles traffic between peered VNets.

4. Virtual Network Gateway Route

• Destination: On-premises networks (via VPN or ExpressRoute).

• Next hop: Virtual network gateway.

• Manages traffic to/from on-premises environments.

5. Private Endpoint Route

• Destination: IP range of a private endpoint.

• Next hop: InterfaceEndpoint.

• Directs traffic to the private IP of a private endpoint.

Customization of System Routes:

If the default system routes don't meet specific needs, you can:

• Override System Routes using User-Defined Routes (UDRs).

  • Attach a route table with custom routes to subnets in your VNet.

• Use Network Virtual Appliances (NVAs) or other solutions as next hops for specific traffic patterns.

Summary

Understanding and managing system routes is key to configuring secure and efficient network traffic in Azure.