Route tables are used to manage and control network traffic of virtual private clouds (VPCs). Proper route configurations enhance network flexibility and security. You can configure routes and specify proper next-hop types to optimize traffic paths, reduce latency, and improve network performance. You can also associate different route tables with different vSwitches to implement traffic control and isolation. This improves network flexibility.
Route table
System route table
After you create a VPC, the system creates a system route table to manage the routes of the VPC. By default, vSwitches in the VPC use the system route table. You cannot create or delete a system route table. However, you can add custom route entries to a system route table.
Custom route table
You can create custom route tables in a VPC, associate custom route tables with vSwitches, and then set vSwitch CIDR blocks as destination CIDR blocks. This way, cloud services in vSwitches can communicate with each other. This facilitates network management. For more information, see Create and manage a route table.
Gateway route table
You can create a custom route table in a VPC and associate the custom route table with an IPv4 gateway. This route table is called a gateway route table. You can use a gateway route table to control traffic from the Internet to a VPC. You can redirect Internet traffic to security devices in the VPC, such as virtual firewalls. This allows you to protect cloud resources in the VPC in a centralized manner. For more information, see Create and manage an IPv4 gateway.
When you manage route tables, take note of the following limits:
Each VPC can contain at most 10 route tables including the system route table.
Only one route table can be associated with each vSwitch. The routing policies of a vSwitch are managed by the route table that is associated with the vSwitch. You can associate one route table with multiple vSwitches.
After you create a vSwitch, the system route table is associated with the vSwitch by default.
If a custom route table is associated with a vSwitch and you want to replace the custom route table with the system route table, you must disassociate the custom route table from the vSwitch. If you want to associate a different custom route table with the vSwitch, you can directly replace the original custom route table without the need to disassociate the original custom route table.
Routes
Each item in a route table is a route. A route consists of the destination CIDR block, the next hop type, and the next hop. The destination CIDR block is the IP address range to which you want to forward network traffic. The next hop type specifies the type of cloud resource that is used to transmit network traffic, such as an Elastic Compute Service (ECS) instance, a VPN gateway, or a secondary elastic network interface (ENI). The next hop is the specific cloud resource that is used to transmit network traffic.
Routes are classified into system routes, custom routes, and dynamic routes.
System routes
System routes are classified into IPv4 routes and IPv6 routes. You cannot modify system routes.
After you create a VPC and vSwitches, the system automatically adds the following IPv4 routes to the route table:
A route whose destination CIDR block is 100.64.0.0/10. This route is used for communication among cloud resources within the VPC.
Routes 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 the VPC.
Destination CIDR block
Next hop
Route type
Description
100.64.0.0/10
-
System route
Created by system.
192.168.1.0/24
-
System route
Created with vSwitch(vsw-m5exxjccadi03tvx0****) by system.
192.168.0.0/24
-
System route
Created with vSwitch(vsw-m5esyy9l8ntpt5gsw****) by system.
If IPv6 is enabled for your VPC, the following IPv6 routes are automatically added to the system route table of the VPC:
A custom route whose destination CIDR block is
::/0and whose next hop is an IPv6 gateway. Cloud resources deployed in the VPC use this route to access the Internet through IPv6 addresses.System routes whose destination CIDR blocks are the same as the IPv6 CIDR blocks of the vSwitches in the VPC. These routes are used for communication among cloud resources within the vSwitches.
NoteIf you create a custom route table and associate the custom route table with a vSwitch that resides in an IPv6 CIDR block, you must add a custom route whose destination CIDR block is
::/0and whose next hop is the IPv6 gateway. For more information, see Add a custom route.
Custom routes
You can add custom routes to replace system routes or route traffic to specified destinations. You can specify the following types of next hops when you create a custom route:
Destination CIDR block
Next hop type
IPv4 CIDR block and VPC prefix list
IPv4 gateway: Traffic that is destined for the destination CIDR block is routed to the specified IPv4 gateway.
NAT gateway: Traffic that is destined for the destination CIDR block is routed to the specified NAT gateway.
You can select this type if you want to access the Internet through a NAT gateway.
VPC peering connection: Traffic that is destined for the destination CIDR block is routed to the specified VPC peering connection.
Transit router: Traffic that is destined for the destination CIDR block is routed to a specified transit router.
VPN gateway: Traffic that is destined for the destination CIDR block is routed to the 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.
ECS instance: Traffic that is destined for the destination CIDR block is routed to the specified ECS instance in the VPC.
You can select this type if you want to access the Internet or other applications through applications that are deployed on the ECS instance.
ENI: Traffic that is destined for the destination CIDR block is routed to the specified ENI.
High-availability virtual IP address (HAVIP): Traffic that is destined for the destination CIDR block is routed to the specified HAVIP.
Router interface (to VBR): Traffic that is destined for the destination CIDR block is routed to the 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.
Router interface (to VPC): Traffic that is destined for the destination CIDR block is routed to the specified VBR.
ECR: Traffic that is destined for the destination CIDR block is routed to the specified Express Connect Router (ECR).
NoteIPv6 CIDR block
ECS instance: Traffic that is destined for the destination CIDR block is routed to the specified ECS instance in the VPC.
You can select this type if you want to access the Internet or other applications through applications that are deployed on the ECS instance.
IPv6 gateway: Traffic that is destined for the destination CIDR block is routed to the specified IPv6 gateway.
You can select this type if you want to implement IPv6 communication through an IPv6 gateway. You can forward traffic to the specified IPv6 gateway only if a route is added to the system route table and an IPv6 gateway is created in the region where the vSwitch associated with the system route table is deployed.
ENI: Traffic that is destined for the destination CIDR block is routed to the specified ENI.
Router interface (to VBR): Traffic that is destined for the destination CIDR block is routed to the specified VBR.
You can select this type if you want to connect a VPC to an on-premises network through Express Connect circuits.
ECR: Traffic that is destined for the destination CIDR block is routed to the specified ECR.
VPC peering connection: Traffic that is destined for the destination CIDR block is routed to the specified VPC peering connection.
Dynamic routes
Dynamic routes are routes learned from dynamic sources through route synchronization. Cloud Enterprise Network (CEN) instances, VPN gateways, and ECRs can serve as dynamic sources.
NoteA VPC can receive dynamic routes only from one dynamic source. For example, if a VPC is associated with an ECR and attached to a CEN instance, you cannot enable route advertisement for the VPC. After you create a VPN gateway and enable automatic route advertisement, BGP routes learned by the VPN gateway are automatically advertised to the VPC system route table. In this case, you cannot associate the VPC with an ECR.
A VPC cannot learn routes whose destination CIDR blocks are the same as or more specific than vSwitch CIDR blocks.
Advertise static routes
Advertise static routes to an ECR
A VPC can advertise static routes to an ECR. You can advertise custom routes configured in a system route table to an ECR. If no route conflicts occur, the data center associated with the ECR can learn the routes.
Malaysia (Kuala Lumpur) now supports the advertisement of static routes to an ECR.
After a VPC is associated with an ECR, system routes of the VPC are advertised to the ECR by default.
After static routes are advertised to the ECR, the routes are advertised to data centers associated with the ECR but are not advertised to other VPCs associated with the ECR.
If conflicts occur between advertised routes, you can view the routes on the Routes tab of the ECR details page. The status of the routes is Conflicting and the routes do not take effect.
When you advertise static routes to an ECR, take note of the following information:
You cannot advertise routes in custom route tables of a VPC to an ECR.
You cannot advertise routes that use prefix lists to an ECR.
You cannot advertise active/standby routes and load balancing routes created by a VPC to an ECR. After VPC routes are advertised to an ECR, you cannot configure the routes as load balancing routes or active/standby routes.
If you modify the route after VPC routes are advertised to an ECR, you can specify only a next hop that supports route advertisement.
The following table describes the default advertisement status of different VPC route types, and whether the route types support advertisement or withdrawal.
Route type
Source instance
Advertised by default
Advertisement
Withdrawal
VPC system routes
VPC
Yes
Supported
Unsupported
Routes that point to IPv4 gateways
VPC
No
Supported
Supported
Routes that point to IPv6 gateways
VPC
No
Supported
Supported
Routes that point to NAT gateways
VPC
No
Supported
Supported
Routes that point to VPC peering connections
VPC
No
Unsupported
Unsupported
Routes that point to transit routers
VPC
No
Unsupported
Unsupported
Routes that point to VPN gateways
VPC
No
Supported
Supported
Routes that point to ECS instances
VPC
No
Supported
Supported
Routes that point to ENIs
VPC
No
Supported
Supported
Routes that point to HAVIPs
VPC
No
Supported
Supported
Routes that point to router interfaces (to VBR)
VPC
No
Unsupported
Unsupported
Routes that point to router interfaces (to VPC)
VPC
No
Unsupported
Unsupported
Routes that point to ECRs
VPC
No
Unsupported
Unsupported
Advertise routes to a transit router
Transit routers support route advertisement. You can advertise the routes of a VPC that is associated with a transit router to the transit router. If no route conflicts occur, other network instances associated with the transit router can learn the routes. For more information about the route status and whether route advertisement is supported for different route types, see Advertise routes to a transit router.
If your VPC uses an ECR and a transit router to build a hybrid cloud, the rules for CEN to advertise routes and for the VPC to advertise static routes to the ECR remain unchanged.
Route priorities
The priorities of routes take effect based on the following rules:
Same destination CIDR block
Load balancing routes are supported only when the next hop type is router interface (to VBR) and must be used with health checks.
Active/standby routes are supported only when the next hop type is router interface (to VBR) and must be used with health checks.
In other cases, the destination CIDR blocks of different routes must be unique. The destination CIDR blocks of custom routes and dynamic routes cannot be the same as those of system routes. The destination CIDR blocks of custom routes cannot be the same as those of dynamic routes.
Overlapping destination CIDR blocks
Network traffic is routed based on the longest prefix match algorithm. The destination CIDR blocks of custom routes and dynamic routes can contain the CIDR blocks of system routes, and the CIDR blocks of custom routes cannot be more specific than the CIDR blocks of system routes, excluding system routes of cloud services. You can create a custom route whose destination CIDR block is more specific than
100.64.0.0/10, but the destination CIDR block cannot be the same as 100.64.0.0/10.ImportantThe system route whose destination CIDR block is
100.64.0.0/10is used for communication within a VPC. We recommend that you configure a more specific route to make sure that your services can run as expected.The following table shows the route table of a VPC. The "-" sign indicates the VPC.
Destination CIDR block
Next hop type
Next Hop
Route type
100.64.0.0/10-
-
System
192.168.0.0/24-
-
System
0.0.0.0/0ECS instance
i-bp15u6os7nx2c9h9****
Custom
10.0.0.0/24ECS instance
i-bp1966ss26t47ka4****
Custom
The routes whose destination CIDR blocks are
100.64.0.0/10and192.168.0.0/24are system routes. The routes whose destination CIDR blocks are0.0.0.0/0and10.0.0.0/24are custom routes. Traffic destined for0.0.0.0/0is forwarded to the ECS instance whose ID isi-bp15u6os7nx2c9h9****, and traffic destined for10.0.0.0/24is forwarded to the ECS instance whose IDis i-bp1966ss26t47ka4****. Based on the longest prefix match algorithm, traffic destined for10.0.0.1is forwarded toi-bp1966ss26t47ka4****, while traffic destined for10.0.1.1is forwarded toi-bp15u6os7nx2c9h9****.
Different destination CIDR blocks
You can specify the same next hop for different routes.
Limits and quotas
Regions that support custom route tables
Area | Supported region |
Asia Pacific | China (Hangzhou), China (Shanghai), China (Nanjing - Local Region), China (Qingdao), China (Beijing), China (Zhangjiakou), China (Hohhot), China (Ulanqab), China (Shenzhen), China (Heyuan), China (Guangzhou), China (Chengdu), China (Hong Kong), China (Wuhan - Local Region), China (Fuzhou - Local Region), Japan (Tokyo), South Korea (Seoul), Singapore, Australia (Sydney), Malaysia (Kuala Lumpur), Indonesia (Jakarta), Philippines (Manila), and Thailand (Bangkok) |
Europe & Americas | Germany (Frankfurt), UK (London), US (Silicon Valley), and US (Virginia) |
Middle East | UAE (Dubai) and SAU (Riyadh - Partner Region) Important The SAU (Riyadh - Partner Region) region is operated by a partner. |
Quotas
Name/ID | Description | Default value | Adjustable |
vpc_quota_route_tables_num | Maximum number of custom route tables that can be created in each VPC | 9 | You can increase the quota by performing the following operations:
|
vpc_quota_route_entrys_num | Maximum number of custom routes that can be created in each route table (dynamic routes are not included) | 200 | |
vpc_quota_dynamic_route_entrys_num | Maximum number of dynamic routes in each route table | 500 | |
vpc_quota_havip_custom_route_entry | Maximum number of custom routes that point to an HAVIP | 5 | |
vpc_quota_vpn_custom_route_entry | Maximum number of custom routes in a VPC that point to a VPN gateway | 50 | |
N/A | Maximum number of tags that can be added to each route table | 20 | No |
Maximum number of vRouters that can be created in each VPC | 1 | ||
Maximum number of routes that can point to a transit router supported by each VPC | 600 |
Examples
You can add custom routes to a route table to control inbound and outbound traffic transmitted over a VPC.
Private VPC route
If the traffic paths of vSwitches are significantly different and the system route table cannot meet your business requirements. You can create a custom route table in your VPC, associate the custom route table with a vSwitch, and specify the vSwitch CIDR block as the destination CIDR block for communication within the vSwitch. This facilitates network management.
Cross-VPC communication (VPC peering connection)
A VPC peering connection is a network connection that connects two VPCs. VPC peering connections support IPv4 and IPv6. You can use VPC peering connections to enable communication between IPv4 and IPv6 traffic. This enables two VPCs to communicate with each other through private networks.
Cross-VPC communication (VPN gateway)
You can use a VPN gateway to establish secure IPsec-VPN connections between two VPCs.
Connect a VPC to an on-premises network through an Express Connect circuit
You can use an Express Connect circuit to connect a data center to the cloud by using a VBR.
You can use an Express Connect circuit and an ECR to connect a data center to a VPC with low latency and high performance.
Connect a VPC to an on-premises network through a VPN gateway
You can use a VPN gateway to connect a data center to a VPC through encrypted tunnels.
References
For more information about how to create and manage route tables, see Create and manage a route table.
For more information about how to manage vSwitch traffic, see Use custom route tables to manage network traffic.