When a network instance connects to a transit router with route advertisement enabled, routes are automatically propagated to the route table of the transit router. But some routes of the VPC are not propagated by default. You can manually advertise these routes to the transit router as needed for connectivity.
Background
The following table lists the default status of VPC routes of different types on a transit router and whether you can advertise or withdraw the routes.
Custom route entries of VPCs cannot be advertised to the transit router.
Route entries of prefix lists cannot be advertised to the transit router.
Route type | Network instance | Advertised to a transit router by default | Supports advertisement and withdrawal |
Routes that point to Elastic Compute Service (ECS) instances | VPC | No | Yes |
Routes that point to VPN gateways | VPC | No | Yes |
Routes that point to high-availability virtual IP addresses (HAVIPs) | VPC | No | Yes |
Routes that point to IPv4 gateways | VPC | No | Yes |
Routes that point to elastic network interfaces (ENIs) | VPC | No | Yes |
Routes that point to IPv6 gateways | VPC | No | Yes |
Routes that point to NAT gateways | VPC | No | Yes |
Routes that point to transit routers | VPC | No | No |
Routes that point to route interfaces (to VBR) | VPC | No | No |
Routes that point to VPC peering connections | VPC | No | No |
Routes that point to Express Connect Router (ECR) | VPC | No | No |
Routes that point to Gateway Load Balancer (GWLB) Endpoint | VPC | No | No |
System routes of VPCs | VPC | Yes | Yes |
By default, Cloud Connect Network (CCN) instances and virtual border routers (VBRs) advertise routes to the transit router to which they are connected. You cannot advertise or withdraw the routes of a CCN instance or a VBR.
100.64.0.0/10in the system route table is used by Alibaba Cloud services and cannot be propagated to the transit router.In a Basic Edition transit router, Cloud Connect Network (CCN) instances and virtual border routers (VBRs) with the next hop pointing to an Express Connect circuit are automatically advertised to the transit router by default and cannot be manually advertised or withdrawn. It also does not forward IPv6 traffic by default. For VPCs, all non-IPv6 routes can be managed according to the rules specified in the table above.
Advertise routes to a transit router
Log on to the CEN console.
On the Instances page, click the ID of the CEN instance that you want to manage.
Go to the tab and click the ID of the transit router that you want to manage.
On the transit router details page, click the Network Routes tab.
On the Network Routes tab, select the network instance and the route table that you want to manage, find the route that you want to advertise, and then click Publish in the Advertisement Status column.
In the Advertise Route message, confirm the information and click OK.
Withdraw routes from a transit router
Log on to the CEN console.
On the Instances page, click the ID of the CEN instance that you want to manage.
Go to the tab and click the ID of the transit router that you want to manage.
On the transit router details page, click the Network Routes tab.
On the Network Routes tab, select the network instance and the route table that you want to manage, find the route that you want to withdraw, and then click Withdraw in the Advertisement Status column.
In the Withdraw Route message, confirm the information and click OK.
Reference
Route learning: Check routes that network instances automatically advertise to the Enterprise Edition transit router after route learning is enabled.