Review system routes
Azure uses system routes to direct network traffic between virtual machines, on-premises networks, and the internet. Information about the system routes is recorded in a route table.
Things to know about system routes
Let's take a closer look at how Azure implements system routes.
Azure uses system routes to control traffic for virtual machines in several scenarios:
- Traffic between virtual machines in the same subnet
- Traffic between virtual machines in different subnets in the same virtual network
- Traffic from virtual machines to the internet
A route table contains a set of rules (called routes) that specifies how packets should be routed in a virtual network.
Route tables record information about the system routes, where the tables are associated to subnets.
Each packet leaving a subnet is handled based on the associated route table.
Packets are matched to routes by using the destination. The destination can be an IP address, a virtual network gateway, a virtual appliance, or the internet.
When a matching route can't be found, the packet is dropped.
Business scenario
Suppose you have a virtual network with two subnets. In this configuration, you can use Azure system routes to control communication between the subnets and between subnets and the internet. A front-end subnet can use a system route to access the internet. A back-end subnet can use a system route to access the front-end subnet. Both subnets access a route table. The following illustration highlights this scenario:
