Configure BGP and BFD to accelerate route convergence - Express Connect

Use case

An enterprise has an on-premises data center in Hangzhou and a VPC in the China (Hangzhou) region. It uses an Express Connect circuit to connect its CPE to a VBR, and the data center and VPC communicate through CEN. To improve availability and speed up route convergence, the enterprise enables BGP dynamic routing and BFD between the data center and the VBR.

Prerequisites

Your on-premises data center is connected to Alibaba Cloud through an Express Connect circuit. Access ECS instances from an on-premises data center over an Express Connect circuit.
A BGP peering relationship is established between your on-premises data center and Alibaba Cloud, and the BGP Peers shows Established. Configure and manage BGP.

Step 1: Configure BFD on the VBR

Log on to the Express Connect console.
In the top navigation bar, select the region where the VBR is deployed. In the left-side navigation pane, click Virtual Border Routers (VBRs).
On the Virtual Border Routers (VBRs) page, find the target VBR and click Edit in the Actions column.
In the Edit VBR panel, set the BFD parameters for the VBR, and then click OK.

This example uses the default BFD settings: Submission Interval is 1000 ms, Reception Interval is 1000 ms, and Detection Time Multiplier is 3.
Enable BFD.
1. On the Virtual Border Routers (VBRs) page, click the ID of the target VBR.
2. Click the BGP Peers tab. Find the target BGP peer and click Edit in the Actions column.
3. In the Modify BGP Peer panel, select Enable BFD, configure the BFD Hop Count, and then click OK.
  
  The BFD hop count is the maximum number of hops a BFD packet can traverse between source and destination. Set this value based on your network topology. Valid values: 1 to 255.
  
  Important
  When you use BFD in a multi-cloud environment or in a direct fiber connection that does not have bridging devices, change the default number of BFD hops from 255 to 1.

Step 2: Configure BFD on your CPE

Note

This example uses an H3C-6820 device. Commands vary by vendor. Contact your CPE vendor for device-specific syntax.

Log on to the CPE and run the following commands to establish a BFD session with the VBR.
```
System-view
Bgp <AS number of the CPE device>
Peer <Alibaba Cloud-side IP address of the VBR> bfd
```
Note
In this example, the Alibaba Cloud-side IP address of the VBR is 10.101.1.2.

Run the display bfd session verbose command to verify the BFD configuration.

If the output shows Session State: Up, the BGP connection between the CPE and the VBR is active and BFD is running.

<CPE> display bfd session verbose
Total Session Num: 1 Up Session Num: 1 Init Mode: Active
IPv4 Session Working Under Ctrl Mode:
Local Discr: 513 Remote Discr: 513
Source IP: 10.101.1.1 Destination IP: 10.101.1.2
Session State: Up
Interface: N/A
Min Tx Inter: 500ms Act Tx Inter: 500ms
Min Rx Inter: 500ms Detect Inter: 2500ms
Rx Count: 135 Tx Count: 135
Connect Type: Indirect Running Up for: 00:00:58
Hold Time: 2457ms Auth mode: None
Detect Mode: Async Slot: 0
Protocol: BGP
Version:1
Diag Info: No Diagnostic

If you have multiple Express Connect circuits, repeat the preceding steps for each circuit.

FAQ

If a CEN instance has two VBRs, can I achieve fast route convergence by configuring BFD on only one of them?

Yes, you can.
If a CEN instance has two VBRs and the one with BFD enabled fails, can fast route convergence still be achieved?

Yes, if both VBRs are in the same failover group. Configure a failover group.