Cloud Enterprise Network (CEN) automatically learns routes from attached networks. If two routes overlap, the conflicted routes will be denied. With overlapping routing enabled, CEN can learn overlapping routes that have the same prefix but different netmasks.

Note For CEN instances that are created after March 1, 2019, the overlapping routing function is enabled by default.

Before overlapping routing is enabled

The following CEN and VPC are used: VPC-A is attached to a CEN instance. A custom route entry with the destination CIDR block of 192.168.1.0/24 and next hop of an ECS instance is added to VPC-A. By default, all routes with IP address 192.168.1.0/x (1<=x<=3) that are published by other networks and learnt by CEN will be denied.

Similarly, if a route with the destination CIDR block 192.168.1.0/24 is learnt by VPC-A from CEN, you cannot create any route with the destination CIDR block 192.168.1.0/x (1 <= x <= 32) in VPC-A, and VPC-A rejects other routes that are sent from CEN with destination CIDR block of 192.168.1.0/x (1 <= x <= 32).

After overlapping routing is enabled

With overlapping routing enabled, CEN can learn overlapping routes that have the same prefix but different netmasks.

For example, a custom route with destination CIDR block of 192.168.1.0/24 and the next hop of ECS1 is added to VPC-A which has been attached to a CEN instance. After you enable overlapping routing, routes that are published from other networks in the CEN instance with destination CIDR block of 192.168.0.0/16 can still be accepted by VPC-A.

Also, the routes with the destination CIDR blocks 168.1.0/24 and 192.168.0.0/16 can be learned by CEN. CEN uses the longest prefix match algorithm to route traffic.

Exception

After the overlapping routing function is enabled, VPC does not accept routes that are subsets of a VSwitch. For example, the CIDR block of a VSwitch is 10.0.0.0/16, then the VPC to which the VSwitch belongs will not accept the routes with the CIDR block 10.0.0.0/24 but will accept the routes with the CIDR block 10.0.0.0/8.

Procedure

To enable the overlapping routing function, follow these steps:

  1. Log on to the CEN console.
  2. Click the ID of the target CEN instance.
  3. In the Basic Settings section, click Enable next to Overlapping Routing Function.


Notice After the overlapping routing function is enabled, it cannot be disabled.