When multiple Express Connect circuits in the same region connect to different access points, the forwarding mode you choose determines how traffic is distributed across those paths. An Express Connect router (ECR) supports two modes: equal-cost multi-path (ECMP) load balancing (default) and nearby forwarding.
Choose a forwarding mode
| ECMP load balancing (default) | Nearby forwarding | |
|---|---|---|
| How traffic is routed | Distributed across all equal-cost paths | Steered to the path closest to the originating zone |
| Primary benefit | Prevents single-path congestion; improves throughput and stability | Minimizes detours; reduces transmission latency |
| Fault behavior | Traffic continues on remaining paths | If one path fails, nearby forwarding becomes invalid and all traffic switches to the remaining path |
ECMP load balancing mode
ECMP load balancing distributes packets across multiple equal-cost paths. This prevents congestion on any single path and improves network resource efficiency and service stability.
For an example architecture that uses ECMP load balancing to build active/active connections between a data center and Alibaba Cloud, see Establish active/active connections between a data center and Alibaba Cloud by using an ECR.
Nearby forwarding mode
Nearby forwarding steers traffic to the optimal path. This minimizes traffic detours and reduces transmission latency.
Contact your account manager to get the zone-to-access-point mappings before enabling this mode. If one of the two paths fails, nearby forwarding automatically becomes invalid and all traffic switches to the remaining path.
If a zone has no nearby access point, traffic for that zone continues to use ECMP load balancing. If an Enterprise Edition transit router (TR) acts as a forwarding gateway in the cloud, create at least two zones in the TR's region before creating a virtual private cloud (VPC) connection to the TR. This minimizes detours between the VPC and the TR. See Announcement: Optimization on VPC-connected Enterprise Edition transit routers and Scenario 1: Your data center needs to communicate with multiple VPCs in the same area, and the VPCs need to communicate with each other.
Change the forwarding mode
Log on to the Express Connect console.
In the left-side navigation pane, click Express Connect Router (ECR). On the Express Connect Router (ECR) page, find the ECR and click its name. The details page appears.
In the Basic Information section, click Edit next to Forwarding Mode.
In the Edit Forwarding Mode among Regions dialog box, select ECMP Load Balancing or Nearby Forwarding, then click OK.
Set up nearby forwarding
Before switching to nearby forwarding, complete the following steps to establish the required Express Connect circuits and ECR associations.
Prerequisites
Before you begin, ensure that you have:
The location of the data center where your cloud resources are deployed (contact your business manager)
The access points for Express Connect circuits in the data center (contact your business manager)
The zone-to-access-point mappings (contact your account manager)
Procedure
Connect to the Alibaba Cloud data center from your access points using Express Connect circuits. See Connect to Alibaba Cloud over a dedicated Express Connect circuit and Overview of hosted connections.
Create Express Connect circuits and virtual border routers (VBRs), and configure Border Gateway Protocol (BGP). See Create and manage a dedicated connection over an Express Connect circuit and Create and manage a VBR.
Create an ECR and associate it with the corresponding VBRs and VPC. See Create and manage an ECR.
Follow the steps in Change the forwarding mode to switch to Nearby Forwarding.
API reference
| API | Description |
|---|---|
| DescribeExpressConnectRouterInterRegionTransitMode | Queries the cross-region forwarding mode of an ECR |
| ModifyExpressConnectRouterInterRegionTransitMode | Modifies the cross-region forwarding mode of an ECR |