This topic describes the routing features of transit routers and how transit routers work.

Routing features of transit routers

Transit routers are core components of Cloud Enterprise Network (CEN). CEN uses transit routers to enable network instances deployed in the current region to communicate with network instances deployed in the same region or different regions. Transit routers support features such as regional route tables, route maps, and cross-region communication. In the CEN console, you can manage the routing features of transit routers such as routing querying, learning, and filtering. You can also use transit routers to connect, isolate, and redirect network traffic based on custom policies. Transit routers support flexible networking and facilitate network management.

Transit routers provide the Basic edition and Enterprise edition based on regions. Transit routers of the Basic edition and Enterprise edition support different features. For more information, see Table 1. For more information about the regions that support Enterprise edition transit routers, see Regions that support Enterprise edition transit routers.

Table 1. Features of transit routers
Routing feature Description Basic edition Enterprise edition Related topic
Default route table After the system creates a transit router, the system automatically creates a default route table. Supported Supported None
Custom route tables An Enterprise edition transit router allows you to create one or more custom route tables. Similar to virtual routing and forwarding (VRF) used in traditional routers, a custom route table is isolated from the default route table and other route tables.

You can isolate traffic by associating a network instance with a custom route table.

Not supported Supported Create a custom route table
Associated forwarding The associated forwarding feature allows you to associate a network instance with a route table. Then, the network instance forwards traffic by querying the route table. Not supported Supported Create associated forwarding correlation
Route learning The route learning feature allows you to associate a network instance with a route table. Then, the network instance advertises its routes to the route table. Not supported Supported Create route learning correlation
Add route entries Enterprise edition transit routers allow you to add static route entries:
  • You can add route entries to route tables of a transit router.
  • You can add route entries to a network instance.
Not supported Supported
Route maps You can configure route maps to filter and modify routes. This allows you to manage network communication in the cloud.

After you add a route map, it is associated with the default route table of a Basic edition or Enterprise edition transit router. You cannot associate a route map with a custom route table of an Enterprise edition transit router.

Supported Supported Overview

How Enterprise edition transit routers work

How Enterprise edition transit routers work

After you create an Enterprise edition transit router in a region, the system automatically creates a custom route table in the region. You can create custom route tables based on your requirements. After you create a custom route table, the network instance forwards traffic by querying the custom route table.

  • Network instances: After you associate a network instance with a transit router, the system associates the network instance with the default route table. The network instance advertises its routes to the default route table. You can use advanced features to create custom route maps for a network instance. For more information, see the following table.
    Network instance type Default routing setting Advanced feature
    VPC When you associate a virtual private cloud (VPC) with a transit router, the system enables the following features by default:
    • Associate with Default Route Table of Transit Router

      After this feature is enabled, the VPC is automatically associated with the default route table of the transit router. The VPC forwards traffic based on the default route table.

    • Propagate System Routes to Default Route Table of Transit Router

      After this feature is enabled, the VPC advertises its routes to the default route table of the transit router to enable instance communication.

    When you create a VPC, you can clear the features that are to be enabled by default. You can create custom route maps by using the following features:
    • Create a custom route table.
    • Set associated forwarding correlation : Associate a network instance with a specified route table.
    • Set routing learning correlation: A network instance advertises its routes to a specified route table.
    • Add route entries: Add static routes or black hole routes to a specified route table.
    VBR When you associate a virtual border router (VBR) with a transit router, the system enables the Propagate Routes to VBR feature by default.

    After this feature is enabled, the VBR is automatically associated with the default route table of the transit router. In this case, the VBR advertises its routes to the default table and the default route table advertises its routes to the VBR.

    When you create a VPC, you can clear the features that are enabled by default. You can create custom route maps by using the following features:
    • Create a custom route table.
    • Set associated forwarding correlation : Associate a network instance with a specified route table.
    • Set routing learning correlation: A network instance advertises its routes to a specified route table.
    • Add route entries: Add static routes or black hole routes to a specified route table.
    CCN When you associate a Cloud Connect Network (CCN) instance with a transit router, the CCN instance is associated with the default route table of the transit router. The default route table learns routes from the CCN instance and advertises its routes to the CCN instance.
    Note You can associate a CEN instance with only the default route table. You cannot associate a CEN instance with a custom route table, set route learning, or add route entries.
    None
  • Cloud services: After you add a cloud service and PrivateZone, the routes of the cloud service and PrivateZone are automatically added to the default route table.
  • Route maps: After you add a route map, the route map is associated with the default route table to filter routes.

How Basic edition transit routers work

How Basic edition transit routers work

After you create a Basic edition transit router in a region, the system automatically creates a custom route table in the region. All network traffic in the region is forwarded by querying the default route table.

  • Network instances: After you associate a network instance with a transit router, the network instance is associated with the default route table of the transit router. The network instance advertises its routes to the default route table and forwards traffic by querying the default route table.
  • Cloud services: After you add a cloud service and PrivateZone, the routes of the cloud service and PrivateZone are automatically added to the default route table.
  • Route maps: After you add a route map, the route map is associated with the default route table to filter routes.