Without route learning, you must manually add routes to a transit router's route table every time you connect a new network instance — and remove them when you disconnect. Route learning automates this: when you enable propagation for a connection, the network instance advertises its routes to the transit router's route table automatically. If you disable propagation, those routes are withdrawn.
This feature is available only on Enterprise Edition transit routers.
How it works
In this example, two Virtual Private Clouds (VPCs) in the China (Hangzhou) region are connected to a transit router. When route propagation is enabled for both VPC connections, the transit router learns the system routes of each VPC and adds them to its default route table automatically.
For traffic to be forwarded correctly, the VPC connections must also be associated with the default route table. Association and propagation are distinct: association controls which route table handles inbound traffic from a connection, while propagation controls which routes a connection advertises to a route table.
Route propagation can be established between:
The route table of an Enterprise Edition transit router and multiple network instances
A network instance and route tables of multiple Enterprise Edition transit routers
Supported edition
Only Enterprise Edition transit routers support route learning. Check the edition of your transit router before proceeding.
Routes advertised by connection type
Each connection type automatically advertises specific routes to the transit router.
| Connection type | Instance type | Automatically advertised routes |
|---|---|---|
| VPC connection | VPC | System routes of the VPC. To propagate custom routes in the VPC's system route table, advertise them to CEN separately. Custom routes in custom route tables of VPCs cannot be advertised to CEN. |
| VBR connection | Virtual border router (VBR) | VBR routes with next hops pointing to Express Connect circuits (visible on the Custom Route Entry tab) and BGP routes (visible on the BGP Route Entry tab). For details, see Add and manage routes. |
| ECR connection | Express Connect Router (ECR) | Routes whose next hop is a VBR. |
| VPN connection | IPsec-VPN connection | Routes in the destination route tables and BGP route tables of the IPsec-VPN connection. |
| Inter-region connection | Transit router | If both the local and peer transit routers are Enterprise Edition and route synchronization is enabled, routes from the peer route table associated with the connection are propagated to the local route table. If the local transit router is Enterprise Edition and the peer is Basic Edition, and route synchronization is enabled, routes from all peer route tables are propagated to the local route table. |
Enable route propagation
Method 1: Enable during connection creation
When creating a network instance connection, select Propagate System Routes to Default Route Table of Transit Router in the Advanced Settings section.
This creates a route learning policy at the same time as the connection. For step-by-step instructions on creating each connection type, see:
Method 2: Enable from the route table
Use this method if:
Propagate System Routes to Default Route Table of Transit Router was not selected when you created the connection, or
A custom route table has been created and you want it to learn routes from a network instance
Log on to the CEN console.
On the Instances page, click the ID of the CEN instance.
Go to the Basic Information > Transit Router tab and click the ID of the transit router.
On the transit router details page, click the Route Table tab.
In the left-side section, click the ID of the route table. On the route table details page, click the Route Propagation tab.
Click Enable Route Propagation. In the dialog box, configure the following parameters and click OK.
| Parameter | Description |
|---|---|
| Route Table | The current route table is selected by default. |
| Transit Router | The current transit router is selected by default. |
| Associated Connection | Select the network instance connection for which to enable route propagation. Once enabled, the network instance advertises routes to this route table. View the propagated routes on the Route Entry tab. |
Disable route propagation
When you disable route propagation, routes advertised from the network instance are automatically withdrawn from the transit router's route table.
Log on to the CEN console.
On the Instances page, click the ID of the CEN instance.
Go to the Basic Information > Transit Router tab and click the ID of the transit router.
On the transit router details page, click the Route Table tab.
In the left-side section, click the ID of the route table. On the route table details page, click the Route Propagation tab.
Find the target network instance connection and click Delete in the Actions column.
In the Disable Route Propagation dialog box, confirm the details and click OK.
API reference
| Operation | Description |
|---|---|
| EnableTransitRouterRouteTablePropagation | Creates a route learning policy. |
| ListTransitRouterRouteTablePropagations | Queries route learning policies of a route table in an Enterprise Edition transit router. |
| DisableTransitRouterRouteTablePropagation | Disables route learning. |
What's next
Associated forwarding — Associate connections with route tables to control traffic forwarding.
Route synchronization — Synchronize routes across inter-region connections.