Cloud Enterprise Network (CEN) automatically learns the routes of the network instances that are attached to a CEN instance. If the destination CIDR blocks of the routes to be learned overlap with an existing one, the routes are conflicting with each other. After you enable overlapping routing, CEN can learn routes with destination CIDR blocks that have the same prefix but different subnet mask lengths.

Note By default, overlapping routing is enabled for CEN instances that are created after March 1, 2019 (UTC+8).

Before overlapping routing is enabled

For example, virtual private cloud (VPC) A attached to a CEN instance has a custom route whose destination CIDR block is 192.168.1.0/24 and the next hop is Elastic Compute Service (ECS) instance 1 in VPC A. In this scenario, VPC A cannot learn the routes whose destination CIDR block is 192.168.1.0/x (1 ≤ x ≤ 32) from other network instances attached to the CEN instance.

Similarly, if VPC A learns a route whose destination CIDR block is 192.168.1.0/24 from the CEN instance, you cannot create a custom route whose destination CIDR block is 192.168.1.0/x (1 ≤ x ≤ 32) for VPC A. VPC A cannot learn other routes whose destination CIDR block is 192.168.1.0/x (1 ≤ x ≤ 32) from other network instances attached to the CEN instance.

After overlapping routing is enabled

After you enable overlapping routing, CEN can learn routes with destination CIDR blocks that have the same prefix but different subnet mask lengths.

For example, VPC A attached to a CEN instance has a custom route whose destination CIDR block is 192.168.1.0/24 and the next hop is ECS 1 in VPC A. In this scenario, VPC A can learn the routes whose destination CIDR block is 192.168.0.0/16 from other network instances attached to the CEN instance.

The routes whose destination CIDR blocks are 192.168.1.0/24 and 192.168.0.0/16 can be learned at the same time by CEN. CEN learns the routes that match the longest prefix algorithm.

Note After you enable overlapping routing, a VPC does not learn the routes whose destination CIDR block is more specific than that of the VPC VSwitch. For example, if the CIDR block of a VPC VSwitch is 10.0.0.0/16, the VPC cannot learn the routes whose destination CIDR block is 10.0.0.0/24 from other network instances. However, the VPC can learn the routes whose destination CIDR block is 10.0.0.0/8 from other network instances.

Procedure

To enable overlapping routing, perform the following operations:

  1. Log on to the CEN console.
  2. On the Instances page, find the CEN instance and click Manage in the Actions column.
  3. In the Basic Settings section, click Enable after Overlapping Routing Function.
  4. In the Enable Overlapping Routing message, click OK.
    Notice You cannot disable overlapping routing after you enable it.