Transit routers provide multiple network communication and route management features. For example, you can use transit routers to connect network instances, create custom route tables, add routes, and add routing policies. This topic describes the features of transit routers and how transit routers work.

Features

Transit routers are available in the following editions: Basic Edition and Enterprise Edition. Basic Edition transit routers and Enterprise Edition transit routers have different features. For more information about the regions that support Enterprise Edition transit routers, see Regions and zones that support Enterprise Edition transit routers. The following table describes the features that are supported by Enterprise Edition and Basic Edition transit routers.

Feature type Feature Description Basic Edition Enterprise Edition References
Basic features Transit routers

A transit router can forward data within the same region or across regions. For a Cloud Enterprise Network (CEN) instance, you can create only one transit router in each region.

When you create a network instance connection in a specified region, the system automatically creates a transit router in the region. You can also manually create a transit router.

Supported Supported Transit routers
Network instances
You can use transit routers to connect the following network instances. This way, you can enable cloud resource communication, cross-region communication, and communication between cloud resources and on-premises resources.
  • Virtual private clouds (VPCs)
  • Virtual border routers (VBRs)
  • Cloud Connect Network (CCN) instances
  • Transit routers
Supported Supported N/A
Network instance connections
A network instance connection refers to the connection between a transit router and a network instance. Network instance connections can be classified into the following types:
  • VPC connection
  • VBR connection
  • CCN instance connection
  • Cross-region connections

    A cross-region connection refers to the connection between transit routers in different regions. You can purchase a bandwidth plan to connect network instances across regions. Network instances in the same region can communicate with each other through transit routers. You do not need to create cross-region connections or purchase bandwidth plans.

Supported Supported
Cross-region connections Bandwidth plans A bandwidth plan provides bandwidth resources to enable cross-region communication. You can use bandwidth plans and the cross-region connection feature of transit routers to enable communication between network instances across different regions. Supported Supported
CCN bandwidth multiplexing The CCN bandwidth multiplexing feature allows you to share cross-region bandwidth resources between a CCN transit router and a region-specific transit router that belongs to the same region. This facilitates configurations and allows you to use bandwidth resources in a more flexible manner. Supported Supported Configure bandwidth multiplexing
Routing Default route tables After the system creates a transit router, the system automatically creates a default route table. Supported Supported N/A
Custom route tables An Enterprise Edition transit router allows you to create one or more custom route tables. Custom route tables are similar to virtual routing and forwarding (VRF) used by traditional routers. A custom route table is isolated from the default route table and other custom route tables.

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

Unsupported Supported Custom route tables
Custom route entries Enterprise Edition transit routers allow you to add static routes and blackhole routes. Unsupported Supported Manage custom routes of a transit router
Associated forwarding You can create an associated forwarding correlation between a network instance connection and a route table of a transit router. After you create an associated forwarding correlation, the transit router forwards traffic of the network instance based on the route table that is associated with the network instance connection. Unsupported Supported Associated forwarding
Route learning You can enable route learning between a network instance connection and a route table of a transit router. After you create a route learning correlation, the route table can automatically learn routes from the network instance. Unsupported Supported Route learning
Routing policies You can configure routing policies to filter and modify routes. This allows you to manage network communication in the cloud.

Routing policies of a Basic Edition transit router are automatically associated with the default route table.

Routing policies of an Enterprise Edition transit router are automatically associated with the default route table or a custom route table.

Supported Supported Routing policy overview
Access to cloud services Access cloud services VBRs or CCN instances that are connected to transit routers can access cloud services deployed on Alibaba Cloud through CEN. Supported Supported Access cloud services
Access PrivateZone Alibaba Cloud DNS PrivateZone (PrivateZone) is a VPC-based resolution and management service for private domain names. VBRs or CCN instances that are connected to transit routers can access PrivateZone deployed on Alibaba Cloud by using the transit routers. Supported Supported Configure PrivateZone
Flow log management Flow logs Flow logs can capture information about cross-region traffic between transit routers. You can analyze cross-region service traffic, troubleshoot network issues, and reduce traffic costs based on the captured information. Unsupported Supported Configure flow logs
Quality of service (QoS) policies Configure QoS policies QoS policies allow you to mark the traffic of different services and set bandwidth throttling. This ensures that your core services have sufficient bandwidth resources and improves network performance. Unsupported Supported Use traffic scheduling to limit bandwidth for inter-region connections

How Enterprise Edition transit routers work

How Enterprise Edition transit routers work

When you create an Enterprise Edition transit router, the system automatically creates a default route table for the transit router. You can create custom routes to forward traffic of network instances in a flexible manner.

  • Network instances: After you create a network instance connection, the system associates the network instance connection with the default route table. The network instance advertises its routes to the default route table. You can use the routing features to create custom routing policies for network instances. The following table provides more details about network instance connections.
    Network instance type Default routing setting Custom routing feature
    VPC connection When you create a VPC connection, the system enables the following features by default:
    • Associate with Default Route Table of Transit Router

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

    • Propagate System Routes to Default Route Table of Transit Router

      After this feature is enabled, the system routes of the VPC are advertised to the default route table of the transit router. This way, the VPC can communicate with other network instances that are connected to the transit router.

    • Automatically Creates Route That Points to Transit Router and Adds to All Route Tables of Current VPC

      After this feature is enabled, the system automatically adds the following three routes to all route tables of the VPC: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. The routes point to the VPC connection.

    When you create a VPC connection, you can disable the features that are enabled by default. You can create custom routing policies by using the following features:
    • Create a custom route table.
    • Create an associated forwarding correlation: Associate a VPC connection with a specified route table.
    • Create a route learning correlation: Advertise the system routes of a VPC to a specified route table.
    • Add routes: Add static routes or blackhole routes to a specified route table.
    VBR connection When you create a VBR connection, the system enables the following features by default:
    • Associate with Default Route Table of Transit Router

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

    • Propagate System Routes to Default Route Table of Transit Router

      After this feature is enabled, the system routes of the VBR are automatically advertised to the default route table of the transit router.

    • Propagate Routes to VBR

      After this feature is enabled, the system automatically advertises the routes in the route table that is associated with the VBR connection to the VBR.

    When you create a VBR connection, you can disable the features that are enabled by default. You can create custom route maps by using the following features:
    • Create a custom route table.
    • Create an associated forwarding correlation: Associate a VBR connection with a specified route table.
    • Create a route learning correlation: Advertise the system routes of a VBR to a specified route table.
    • Add route entries: Add static routes or blackhole routes to a specified route table.
    CCN connection When you create a CCN connection, 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. N/A
    Cross-region connections When you create a cross-region connection, the system enables the following features by default:
    • Associate with Default Route Table of Transit Router

      After this feature is enabled, the inter-region connection is automatically associated with the default route table of the transit router. The transit router uses the default route table to forward network traffic across regions.

    • Propagate System Routes to Default Route Table of Transit Router

      After this feature is enabled, the inter-region connection advertises system routes to the default route table of the transit router.

    • Automatically Advertise Routes to Peer Region

      After this feature is enabled, the routes of the transit router deployed in the current region are automatically advertised to the route table of the peer transit router. The routes are used for inter-region communication between network instances.

    When you create a cross-region connection, you can disable the features that are enabled by default. You can create custom route maps by using the following features:
    • Create a custom route table.
    • Create an associated forwarding correlation: Associate a cross-region connection with a specified route table.
    • Create a route learning correlation: Advertise the system routes of a network instance to a specified route table.
  • Routing policies: When you add a routing policy, you can associate the routing policy with the default route table or a custom route table. The routing policy filters only the routes in the route table to which it is associated.

How Basic Edition transit routers work

How Basic Edition transit routers work

When you create a Basic Edition transit router, the system automatically creates a default route table for the transit router. Traffic of all network instances in the destination region is forwarded through the default route table of the Basic Edition transit router.

  • Network instances: After you create a network instance connection on a transit router, the network instance is associated with the default route table of the transit router. The network instance advertises system routes to the default route table and forwards traffic by querying the default route table.
  • Cloud services: After you add a cloud service or PrivateZone to a transit router, the routes of the cloud service or PrivateZone are automatically added to the default route table. This way, the network instances that are connected to the transit router can use the default route table to access the cloud service or PrivateZone.
  • Routing policies: After you add a routing policy to a transit router, the routing policy is associated with the default route table of the transit router to filter the routes in the default route table.

Regions and zones that support Enterprise Edition transit routers

Transit routers are available in two editions based on regions: the basic edition and the enterprise edition. The following table describes the regions and zones that support Enterprise Edition transit routers. By default, regions and zones that are not listed in the following table support Basic Edition transit routers.

Table 1. Regions and zones that support Enterprise Edition transit routers
Area Region Zone
Chinese mainland China (Hangzhou) Zone H and Zone I
China (Shanghai) Zone F and Zone G
China (Nanjing - Local Region) Zone A
China (Shenzhen) Zone D and Zone E
China (Heyuan) Zone A and Zone B
China (Guangzhou) Zone A and Zone B
China (Qingdao) Zone B and Zone C
China (Beijing) Zone H and Zone G
China (Zhangjiakou) Zone A and Zone C
China (Hohhot) Zone A and Zone B
China (Ulanqab) Zone A and Zone B
China (Chengdu) Zone A and Zone B
Asia Pacific Singapore (Singapore) Zone B and Zone C
China (Hong Kong) Zone B and Zone C
Malaysia (Kuala Lumpur) Zone A and Zone B
India (Mumbai) Zone A and Zone B
Indonesia (Jakarta) Zone A and Zone B
Philippines (Manila) Zone A
Japan (Tokyo) Zone A and Zone B
Europe Germany (Frankfurt) Zone A and Zone B
UK (London) Zone A and Zone B
North America US (Virginia) Zone A and Zone B
US (Silicon Valley) Zone A and Zone B
Australia Australia (Sydney) Zone A and Zone B