After you create a virtual private cloud (VPC), the system creates a system route table for the VPC and adds system routes to the route table. The system routes are used to route traffic within the VPC. You cannot create or delete system routes. However, you can create custom routes to route traffic from specific CIDR blocks to a specified destination.

Route tables

System route tables

After you create a VPC, the system creates a system route table to manage routes of the VPC. By default, vSwitches in the VPC use the system route table. You cannot create or delete a system route table.

Custom route tables

You can create a custom route table in a VPC and associate the custom route table with a vSwitch. This allows you to manage networks in a more flexible way. For more information, see Create a custom route table.

Regions that support custom route tables

The following table describes the regions that support custom route tables by default.
Area Supported region
Asia Pacific China (Qingdao), China (Zhangjiakou), China (Hohhot), China (Ulanqab), China (Shanghai), China (Heyuan), China (Guangzhou), China (Chengdu), China (Hong Kong), Japan (Tokyo), Singapore (Singapore), Australia (Sydney), Malaysia (Kuala Lumpur), and Indonesia (Jakarta)
Europe & Americas US (Silicon Valley), US (Virginia), Germany (Frankfurt), and UK (London)
Middle East & India India (Mumbai) and UAE (Dubai)
The custom route table feature is in public preview in the following regions. You can apply for participating in the public review.
Area Supported region
Asia Pacific China (Beijing), China (Shanghai), and China (Shenzhen)

Limits

  • Each VPC can contain at most 10 route tables including the system route table.
  • Each vSwitch can be associated with only one route table. The routing policies of a vSwitch are managed by the route table that is associated with the vSwitch.
  • By default, a vSwitch is associated with the system route table after you create the vSwitch.
  • If you want to associate the system route table with a vSwitch that is associated with a custom route table, you must disassociate the custom route table from the vSwitch. Before you can associate other route tables with the vSwitch, you must disassociate the current route table from the vSwitch.
  • Custom route tables do not support active or standby routes or load-balancing routes.

Route entries

Each item in a route table is a route entry. A route entry specifies the destination for network traffic, and consists of the destination CIDR block, next hop type, and next hop. Route entries include system route entries and custom route entries.

System routes

After you create a VPC, the system automatically adds the following system routes to the route table:
  • A route entry with a destination CIDR block of 100.64.0.0/10. This route is used for communication among cloud resources within the VPC.
  • Route entries whose destination CIDR blocks are the same as the CIDR blocks of the vSwitches in the VPC. These routes are used for communication among cloud resources within the vSwitches.
For example, if you create a VPC whose CIDR block is 192.168.0.0/16 and two vSwitches whose CIDR blocks are 192.168.1.0/24 and 192.168.0.0/24, the following system routes are automatically added to the route table of the VPC. The "-" sign in the following table indicates that the item is not applicable.
Destination CIDR block Next hop Route entry type
100.64.0.0/10 - System route
192.168.1.0/24 - System route
192.168.0.0/24 - System route

Custom routes

You can add custom routes to replace system routes or route traffic to a specified destination. You can specify the following types of next hops when you create a custom route:
  • Elastic Compute Service (ECS) instance: Traffic that is destined for the destination CIDR block is routed to a specified ECS instance in the VPC.

    You can select this type if you want to access the Internet or other applications through the applications deployed on the ECS instance.

  • VPN gateway: Traffic destined for the destination CIDR block is routed to a specified VPN gateway.

    You can select this type if you want to connect a VPC to another VPC or an on-premises network through the VPN gateway.

  • NAT gateway: Traffic destined for the destination CIDR block is routed to a specified NAT gateway.

    You can select this type if you want to connect a VPC to the Internet through the NAT gateway.

  • Router interface (to VPC): Traffic that is destined for the destination CIDR block is routed to a specified VPC.

    You can select this type if you want to connect two VPCs through Express Connect circuits.

  • Router interface (to VBR): Traffic that is destined for the destination CIDR block is routed to a specified virtual border router (VBR).

    You can select this type if you want to connect a VPC to an on-premises network through Express Connect circuits.

  • Secondary ENI: Traffic that is destined for the destination CIDR block is routed to a specified secondary elastic network interface (ENI).
  • IPv6 gateway: Traffic that is destined for the destination CIDR block is routed to a specified IPv6 gateway.

    You can select this type if you want to implement IPv6 communication through an IPv6 gateway.

IPv6 routes

If IPv6 is enabled for your VPC, the following route entries are automatically added to the system route table of the VPC:
  • A custom route entry whose destination CIDR block is ::/0 and whose next hop is the IPv6 gateway. Cloud resources deployed in the VPC use this route to access the Internet through IPv6 addresses.
  • A system route entry of which the destination CIDR block is the IPv6 CIDR block of a vSwitch. This route is used for communication within the vSwitch.
    Note If you create a custom route table and associate the custom route table with a vSwitch for which IPv6 CIDR block is enabled, you must add a custom route entry of which the destination CIDR block is ::/0 and the next hop is the IPv6 gateway instance. For more information, see Add a custom route entry.

Routing rules

If multiple route entries match the destination CIDR block, the route entry with the largest prefix prevails and determines the next hop. This ensures that the traffic is routed to the most precise destination.

The following table shows the route table of a VPC. The "-" sign indicates that the item is not applicable.
Destination CIDR block Next hop type Next hop Route entry type
100.64.0.0/10 - - System route
192.168.0.0/24 - - System route
0.0.0.0/0 Instance i-12345678 Custom route
10.0.0.0/24 Instance i-87654321 Custom route

The route entries that are destined for 100.64.0.0/10 and 192.168.0.0/24 are system route entries. The route entries that are destined for 0.0.0.0/0 and 10.0.0.0/24 are custom route entries. Traffic that is destined for 0.0.0.0/0 is routed to the ECS instance i-12345678, whereas traffic that is destined for 10.0.0.0/24 is routed to the ECS instance i-87654321. Based on the preceding rule, traffic that is destined for 10.0.0.1 is routed to the ECS instance i-87654321, whereas traffic that is destined for 10.0.1.1 is routed to the ECS instance i-12345678.

Limits

Item Default limit Quota increase
Number of vRouters that can be created in each VPC 1 N/A
Number of custom route tables that can be created in each VPC 9

You can go to the Quota Management page to increase the quota. For more information, see Manage service quotas.

Number of custom route entries that can be created in each route table 48
VPCs that do not support custom route tables VPCs that contain ECS instances of the following instance families:

ecs.c1, ecs.c2, ecs.c4, ecs.ce4, ecs.cm4, ecs.d1, ecs.e3, ecs.e4, ecs.ga1, ecs.gn4, ecs.gn5, ecs.i1, ecs.m1, ecs.m2, ecs.mn4, ecs.n1, ecs.n2, ecs.n4, ecs.s1, ecs.s2, ecs.s3, ecs.se1, ecs.sn1, ecs.sn2, ecs.t1, and ecs.xn4.

For more information, see Advanced VPC features.

Upgrade or release an Elastic Compute Service (ECS) instance that does not support advanced network features.
Number of tags that can be added to each route table 20

Examples

You can add custom route entries to a route table to control inbound and outbound traffic that are transmitted over the VPC.

  • Routes within a VPC
    On-premises routesThe preceding figure shows a NAT gateway that is deployed on an ECS instance (ECS 01) in a VPC. To enable the cloud resources in the VPC to access the Internet through the ECS instance, you must 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 two VPCs through Express Connect
    Express Connect routesThe preceding figure shows that VPC 1 (172.16.0.0/12) is connected to VPC 2 (192.168.0.0/16) through Express Connect. After you create router interfaces, you must add the following route entries to the VPCs:
    • Add the following route entry to VPC 1
      Destination CIDR block Next hop type Next hop
      192.168.0.0/16 Router interface (to VPC) VPC2
    • Add the following route entry to VPC 2
      Destination CIDR block Next hop type Next hop
      172.16.0.0/12 Router interface (to VPC) VPC1
  • Connect two VPCs through a VPN gateway
    VPN gateway routesThe preceding figure shows that VPC 1 (172.16.0.0/12) is connected to VPC 2 (10.0.0.0/8) through a VPN gateway. After you configure the VPN gateway, you must add the following route entries to the VPCs.
    • Add the following route entry to VPC 1
      Destination CIDR block Next hop type Next hop
      10.0.0.0/8 VPN gateway VPN gateway 1
    • Add the following route entry to VPC 2
      Destination CIDR block Next hop type Next hop
      172.16.0.0/12 VPN gateway VPN gateway 2
  • Connect a VPC to a data center through Express Connect
    VBR routesThe preceding figure shows that a VPC is connected to an on-premises network through Express Connect. After you configure a connection over an Express Connect circuit and a VBR, you must add the following route entries:
    • Add the following route entry to the VPC
      Destination CIDR block Next hop type Next hop
      192.168.0.0/16 Router interface (to VBR) Router interface RI 1
    • Add the following route entry to the VBR
      Destination CIDR block Next hop type Next hop
      192.168.0.0/16 Express Connect circuit Router interface RI 3
      172.16.0.0/12 VPC Router interface RI 2
    • Add the following route entry to the on-premises network
      Destination CIDR block Next hop type Next hop
      172.16.0.0/12 On-premises gateway On-premises gateway device
  • Connect a VPC to a data center through a VPN gateway
    On-premises VPN gatewayThe preceding figure shows that a VPC (172.16.0.0/12) is connected to a data center (192.168.0.0/16) through a VPN gateway. After you configure the VPN gateway, you must add the following route entry to the VPC.
    Destination CIDR block Next hop type Next hop
    192.168.0.0/16 VPN gateway The configured VPN gateway