After you create a virtual border router (VBR), the system automatically creates a route table for the VBR. You can add route prefixes to the route table and manage the route prefixes in the route table.
Use scenarios
Route prefixes are commonly used in the following scenarios:
Security matrix management
When an Express Connect circuit is connected to a data center, the firewall deployed in the data egress filters inbound traffic to ensure network security. If a large number of specific routes are advertised from Alibaba Cloud, the complexity and number of security rules increase. To simplify the firewall configuration, you need to advertise general routes instead of specific routes from Alibaba Cloud.
Multi-cloud environments
Alibaba Cloud connects its platform to a third-party cloud service provider through an Express Connect circuit. The number of BGP routes that the cloud service provider can accept is limited. In this case, Alibaba Cloud can aggregate the specific routes and then advertise the aggregated routes to the cloud service provider. This ensures that the cloud service provider can accept BGP routes advertised from Alibaba Cloud when the quota on BGP routes is limited.
Hybrid cloud environments
A data center is connected to a virtual private cloud (VPC) and the VPC is divided into a large number of subnets. For example, the VPC contains 24 vSwitches that reside in 192.168.1.0/24. BGP routing is configured between the VBR and data center. The VBR advertises routes destined for 24 CIDR blocks to the data center. This greatly increases the cost of route management and maintenance. To resolve this issue, you can use route prefixes to aggregate specific routes into general routes.
Prerequisites
A VBR is created. For more information, see the Create a VBR section of the "Create and manage a VBR" topic.
The VBR is attached to a Cloud Enterprise Network (CEN) instance and the billing for outbound data transfer is enabled for the VBR. For more information, see the Attach a VBR to a CEN instance section of the "Connect to a VPC" topic and the Enable billing for outbound data transfer section of the "Outbound data transfer fee" topic.
Usage notes
You can add up to 20 route prefixes. You can request a quota increase in the Express Connect console. For more information, see the Adjust quotas section of the "Manage Express Connect quotas" topic.
If a VBR is not created by the owner of the corresponding Express Connect circuit, the owner cannot manage the route prefixes in the route table of the VBR.
After you add a route prefix, the system automatically withdraws the routes that the VBR learns from the CEN instance, and advertises only routes that match the route prefix. After you delete all route prefixes from a VBR, the route prefix feature is disabled for the VBR. Then, the VBR restores all specific routes that it learns from Alibaba Cloud and advertises the routes to your VBR.
After you add route prefixes to a VBR, the VBR does not withdraw the following routes: custom routes, manually advertised BGP routes, and BGP routes learned from on-premises networks.
After you add a route prefix to a VBR, an Express Connect Router (ECR) , you cannot add the VBR to ECR. If you want to add a VBR to ECR, clear the prefix route that is configured for the VBR.
Add route prefixes
Log on to the Express Connect console.
In the top navigation bar, select a region and click Virtual Border Routers (VBRs) in the left-side navigation pane.
On the Virtual Border Routers (VBRs) page, find the VBR that you want to manage and click its ID.
On the VBR details page, choose .
Click Add Route Prefix. In the Add Route Prefix dialog box, enter the route prefixes that you want to advertise from the VBR to the on-premises network, select the agreement, and then click OK.
In the message that appears, check whether the operation causes route flapping and click OK.
Update route prefixes
Before you update route prefixes, make sure that the following requirements are met:
Route prefixes exist on the Specified Synchronized Routes tab.
The new route prefixes that you want to use cannot conflict with the existing route prefixes.
Log on to the Express Connect console.
In the top navigation bar, select a region and click Virtual Border Routers (VBRs) in the left-side navigation pane.
On the Virtual Border Routers (VBRs) page, find the VBR that you want to manage and click its ID.
On the VBR details page, choose .
Click Update Prefix List. In the Update Prefix List dialog box, enter the new route prefixes that you want to use, select the agreement, and then click OK.
In the message that appears, check whether the operation causes route flapping and click OK.
View reference records of route prefixes
Log on to the Express Connect console.
In the top navigation bar, select a region and click Virtual Border Routers (VBRs) in the left-side navigation pane.
On the Virtual Border Routers (VBRs) page, find the VBR that you want to manage and click its ID.
On the VBR details page, choose .
Click Historical Records. On the Historical Records page, you can search records or reference route prefixes in the records.
Search records
Enter a route prefix into the search box and click the
icon to find all records that contain the route prefix. Reference route prefixes in the records
Click a record and then click Reference This Version.
In the Update Prefix List dialog box, select the agreement and then click OK.
In the message that appears, check whether the operation causes route flapping and click OK.
Return to the VBR details page. Then, you can find the referenced route prefix.
Delete route prefixes
Log on to the Express Connect console.
In the top navigation bar, select a region and click Virtual Border Routers (VBRs) in the left-side navigation pane.
On the Virtual Border Routers (VBRs) page, find the VBR that you want to manage and click its ID.
On the VBR details page, choose .
Find the route prefix that you want to delete and click Delete in the Actions column.
In the message that appears, check whether the operation causes route flapping and affects business stability and then click OK.