After you create a Virtual Border Router (VBR), the system automatically creates a route table for the VBR. You can add and manage Specified Synchronized Routes (route prefixes) in the route table.
Use cases
This section describes the common use cases for configuring Specified Synchronized Routes (route prefixes) on a VBR.
Simplify security management
If Alibaba Cloud advertises a large number of specific routes, configuring security rules becomes significantly more complex. You can instead advertise a summary route from the cloud to your data center. This allows your firewall to use a single security rule for the summary route, simplifying configuration.
Multi-cloud connectivity
In a multi-cloud environment where Alibaba Cloud connects to another cloud service provider through an Express Connect circuit, the other provider may limit the number of BGP routes it can accept. You can use Specified Synchronized Routes to aggregate multiple specific routes into a single summary route. This ensures that the other cloud service provider can accept all necessary routes from Alibaba Cloud while staying within their BGP route quota.
Hybrid cloud networking
In a hybrid cloud, your data center is connected to a VPC with complex services and many subnets. For example, a VPC may have 24 vSwitches, each with a /24 CIDR block. If BGP is configured between the VBR and the data center, the VBR will advertise 24 specific routes to your data center. This increases the cost and complexity of route management. By configuring a route prefix, you can advertise a single summary route that covers all specific subnets.
Prerequisites
You have created a Virtual Border Router (VBR). For more information, see Create a VBR instance.
You have attached the VBR to a Cloud Enterprise Network (CEN) instance and enabled outbound data transfer fees for the VBR. For more information, see Attach a VBR to a CEN instance and Enable outbound data transfer fees.
Limitations
You can add a maximum of 20 route prefixes. To increase this quota, submit a request in the Express Connect console. For more information, see Increase a quota.
In a cross-account scenario, the owner of the physical connection port cannot manage route prefixes for the cross-account VBR.
After you add a route prefix, the system automatically withdraws the routes that the VBR learns from Cloud Enterprise Network (CEN) and advertises only the routes that fall within the specified route prefixes. If you delete all route prefixes, this feature is disabled. The VBR then resumes learning all specific routes from the cloud and advertises them to your data center router.
Custom routes, manually advertised BGP routes, and BGP routes learned from your data center are not withdrawn after you add a route prefix.
You cannot add a VBR to an Express Connect Router (ECR) if the VBR has route prefixes configured. To add the VBR to an ECR, you must first delete all configured route prefixes from the VBR.
Add route prefixes
Log on to the Express Connect console.
In the top navigation bar, select the target region. In the left-side navigation pane, click Virtual Border Routers (VBRs).
On the Virtual Border Routers (VBRs) page, click the ID of the target VBR instance.
On the Virtual Border Router details page, select .
Click Add Route Prefix. In the Add Route Prefix dialog box, enter the route prefixes that you want to advertise from the VBR to your data center, select the check box to agree to the terms, and then click OK.
In the confirmation dialog box, verify that the new route prefixes will not cause route flapping, and then click OK.
Update route prefixes
Before you begin, make sure that:
At least one route prefix exists on the Specified Synchronized Routes tab.
The route prefixes that you enter do not duplicate an existing route prefix.
Log on to the Express Connect console.
In the top navigation bar, select the target region. In the left-side navigation pane, click Virtual Border Routers (VBRs).
On the Virtual Border Routers (VBRs) page, click the ID of the target VBR instance.
On the Virtual Border Router details page, select .
Click Update Prefix List. In the Update Prefix List dialog box, enter the updated route prefixes, select the check box to agree to the terms, and then click OK.
In the confirmation dialog box, verify that the updated route prefixes will not cause route flapping, and then click OK.
View historical records
Log on to the Express Connect console.
In the top navigation bar, select the target region. In the left-side navigation pane, click Virtual Border Routers (VBRs).
On the Virtual Border Routers (VBRs) page, click the ID of the target VBR instance.
On the Virtual Border Router details page, select .
Click Historical Records. On the Historical Records page, you can search for a historical record or apply a historical version.
Search historical records
Enter a route prefix in the search box and click the
icon to search for all historical versions that contain the route prefix.Apply a historical version
Click the tab of a historical version and then click Reference This Version.
In the Update Prefix List dialog box, confirm the route prefixes to be updated, select the check box to agree to the terms, and then click OK.
In the confirmation dialog box, verify that the updated route prefixes will not cause route flapping, and then click OK.
You return to the VBR details page, where the route prefix list is updated with the selected historical version.
Delete a route prefix
Log on to the Express Connect console.
In the top navigation bar, select the target region. In the left-side navigation pane, click Virtual Border Routers (VBRs).
On the Virtual Border Routers (VBRs) page, click the ID of the target VBR instance.
On the Virtual Border Router details page, select .
Find the route prefix that you want to delete and click Delete in the Actions column.
In the confirmation dialog box, verify that deleting the route prefix will not cause route flapping or affect service stability, and then click OK.