Route overview

Route tables

After a VPC is created, the system creates a default route table to control routes of the VPC and all VSwitches in the VPC use the route table by default. You cannot create or delete the default route table. However, you can create a custom route table and attach it to the VSwitch to control the routes of the subnet.

A route entry specifies the destination of the traffic and consists of the destination CIDR block, the next hop type, and the next hop. Route entries include system route entries and custom route entries.

System routes

Custom routes

You can add custom route entries to replace system route entries or route traffic to a specified destination. You can specify the following next hop types when creating a custom route entry:

• ECS instance: Route the traffic pointing to the destination CIDR block to an ECS instance in the VPC.

  Select this type when you want to access the Internet or other applications through the application deployed on the ECS instance.

• VPN Gateway: Route the traffic pointing to the destination CIDR block to a VPN Gateway.

  Select this type when you want to connect to another VPC or an on-premises data center through VPN Gateway.

• Router Interface (To VPC): Route the traffic pointing to the destination CIDR block to a VPC.

  Select this type when you want to connect two VPCs through router interfaces of Express Connect.

• Router Interface (To VBR): Route the traffic pointing to the destination CIDR block to a VBR.

  Select this type when you want to connect a VPC to a local data center through Express Connect (physical access).

• Secondary ENI: Route the traffic pointing to the destination CIDR block to a secondary ENI.

IPv6 routes

Routing rules

The longest prefix match is used to route traffic when more than one route entries match the destination CIDR block. The route entry with the longest subnet mask (the most specific route) is used.

The route table of a VPC is as follows:

The route entries destined for 100.64.0.0/10 and 192.168.0.0/24 CIDR blocks are system route entries. The route entries destined for the 0.0.0.0/0 and 10.0.0.0/24 CIDR blocks are custom route entries. Traffic destined for 0.0.0.0/0 will be routed to the ECS instance i-12345678, and traffic destined for 10.0.0.0/24 will be routed to the ECS instance i-87654321. According to the longest prefix match algorithm, traffic destined for 10.0.0.1 will be routed to the ECS instance i-87654321, and traffic destined for 10.0.1.1 will be routed to the ECS instance i-12345678.

Routing examples

You can add custom route entries to the route table to control traffic.

• Routing within a VPC

  As shown in the following figure, a self-built NAT Gateway is deployed on an ECS instance (ECS01) in a VPC. To enable cloud resources in the VPC to access the Internet through this ECS instance, add the following route entry to the route table:

  Destination CIDR block	Next hop type	Next hop
  0.0.0.0/0	ECS instance	ECS01

  
  
  

• Connect VPCs (Express Connect)

  As shown in the following figure, when using Express Connect to connect VPC 1 (172.16.0.0/12) and VPC 2 (192.168.0.0/16), you must add the following route entries in the VPCs after creating route interfaces:

  • Route entry added to VPC1

    Destination CIDR block	Next hop type	Next hop
    192.168.0.0/16	Router interface (To VPC)	VPC2

  • Route entry added to VPC2

    Destination CIDR block	Next hop type	Next hop
    172.16.0.0/12	Router interface (To VPC)	VPC1