Configure health checks to detect Express Connect circuit connectivity - Cloud Enterprise Network

After you connect a Virtual Border Router (VBR) to a Cloud Enterprise Network (CEN) instance, you can configure health checks to monitor Express Connect circuit connectivity. When redundant routes exist, health checks trigger automatic route switchover upon circuit failure to keep traffic flowing.

Background

How it works

Health check mechanism

After you configure a health check for a VBR, Alibaba Cloud sends a ping packet every 2 seconds from the source IP address to the destination IP address in your data center. If the packet returns along the same path, the circuit is healthy. If eight consecutive packets go unanswered or return through a different path, the circuit is considered failed.

Health checks do not send failure notifications. Configure alert rules for your Express Connect circuits so that the system notifies you when issues occur.

Warning

The destination IP address must be able to respond to ping probes. Your data center must not rate-limit or block ping probes.
If your data center devices use Control Plane Policing (CoPP) (for example, Cisco devices) or an anti-attack policy, probe packets may be dropped, causing health check status to flap. Disable CoPP rate limiting on these devices.

Redundant Express Connect circuits

Health check route switchover

When your data center connects to Alibaba Cloud through multiple Express Connect circuits, use the Switch Route feature to enable automatic route switchover. When enabled, a detected failure on one circuit triggers automatic switchover to a healthy circuit.

If the VBR uses static routing, you must configure a health check and enable Switch Route for automatic route switchover. Route switchover is supported only between multiple Express Connect circuits, not between other connection types such as Express Connect and IPsec-VPN.

Prerequisites

The VBR associated with the Express Connect circuit is connected to a CEN instance. Create a VBR connection.

Step 1: Add a health check

Log on to the CEN console.
In the left-side navigation pane, click VBR Health Check.
On the VBR Health Check page, select the region where the VBR instance is located, and then click Add Health Check.

In the Add Health Check dialog box, configure the following parameters and then click OK.

Parameter	Description
CEN Instance	Select the CEN instance to which the VBR is connected.
Virtual Border Router (VBR)	Select the VBR instance that you want to monitor.
Source IP	Configure the source IP address in one of the following ways: Automatic IP Address (Recommended): The system automatically allocates an IP address from the 100.96.0.0/16 CIDR block. Custom IP Address: Specify an unused IP address from the 10.0.0.0/8, 192.168.0.0/16, or 172.16.0.0/12 CIDR block. The address must not conflict with any IP address used in the CEN instance or with the Alibaba Cloud Side IPv4 Address or Data Center Side IPv4 Address of the VBR. Note For the Automatic IP Address method: The following regions support automatic source IP allocation for up to 16 VBRs. Click to view region informationUS (Silicon Valley), China (Hong Kong), US (Virginia), China (Beijing), China (Shanghai), China (Shenzhen), Singapore, China (Hangzhou), China (Heyuan), China (Chengdu), China (Zhangjiakou), Germany (Frankfurt), Malaysia (Kuala Lumpur), UK (London), China (Qingdao), Indonesia (Jakarta), China (Hohhot), China (Guangzhou), China (Ulanqab), China (Nanjing - Local Region), and Japan (Tokyo). The following regions support up to 8 VBRs: Philippines (Manila), South Korea (Seoul), China (Fuzhou - Local Region), Thailand (Bangkok), Mexico, , and Saudi Arabia (Riyadh). After you configure the health check, CEN advertises a route for the source IP address (with a 32-bit subnet mask) to the VBR, regardless of the allocation method. If BGP is used between the VBR and your data center, this route is advertised to your data center through BGP.
Destination IP	The IP address of a ping-responsive device in your data center.
Probe Interval (Seconds)	Interval between consecutive probe packets. Unit: seconds. Valid values: 2 to 3. Default value: 2.
Failure Threshold	Number of consecutive failed probes before the connection is considered unhealthy. Unit: packets. Valid values: 3 to 8. Default value: 8.
Switch Route	Enables or disables automatic route switchover. Enabled by default. When a health check detects a circuit failure and redundant routes exist, traffic is immediately switched to an available link. If disabled, the health check only probes the link without triggering route switchover on failure. Warning If you disable this feature, ensure that other redundancy measures are in place. Otherwise, an Express Connect circuit failure causes a network interruption.
Description	Enter a description for the health check.

Step 2: Configure your data center

Add the following health check configurations in your data center.

Add a return route for the health check probe packets in your data center.
Important
- If your VBR instance uses Border Gateway Protocol (BGP), Alibaba Cloud automatically advertises the health check source IP address (/32) to your data center. No manual return route is needed.
- If your VBR instance uses static routing, manually add a route in your data center with the health check source IP address (/32) as the destination and the Alibaba Cloud-side IP of the Express Connect circuit as the next hop. Without this route, ping packets cannot return along the original path, and Alibaba Cloud incorrectly determines the circuit is unavailable.
The following example shows how to add a return route for probe packets. Consult your device vendor for the actual command.
```
# Add a return route for the health check probe packets.
ip route <health_check_source_ip> 255.255.255.255 <alibaba_cloud_ip_on_vbr_connection>
```
Add a health check configuration in your data center.
Use Bidirectional Forwarding Detection (BFD) or Network Quality Analyzer (NQA) to monitor Express Connect circuit connectivity from your end. Consult your device vendor for specific commands.
Important
- Do not use the Alibaba Cloud-side IPv4 interconnection IP address of the VBR as the NQA probe destination. This can cause false failovers or missed failovers. Use the health check source IP address from Step 1 as the probe destination (ICMP only).
- If your Express Connect circuit lacks redundancy, configure a summary route to the cloud that is independent of NQA probe results. This ensures traffic forwarding continues if an NQA probe fails but the circuit is still up.
Configure health check-based route association in your data center.

If your data center connects to Alibaba Cloud through multiple Express Connect circuits, configure health check-based route association to enable automatic route switching based on health check results. Consult your device vendor for specific commands.

Step 3: Add an alert rule

After you configure the health check, add an alert rule for the Express Connect circuit so that the system notifies you when issues occur.

Log on to the Cloud Monitor console.
In the left-side navigation pane, choose Alerts > Alert Rules.
On the Alert Rules page, click Create Alert Rule.

In the Create Alert Rule panel, set Product to CEN-VBR, configure the alert rule parameters, and then click Confirm.

Only key parameters are described here. For other parameters, see Create an alert rule.

Click Add Rule and select a metric type for the threshold-based alert rule. This topic uses Simple Metric as an example. In the Configure Rule Description panel that appears, configure the following parameters and click OK.

Parameter	Description
Alert Rule	The name of the threshold-based alert rule.
Metric Type	The metric type. This topic uses Simple Metric as an example. For other metric types, see Create an alert template. Simple Metric Combined Metrics Expression Dynamic Threshold
Metric	Select a metric to monitor. VBRHealthyCheckLatencyThe communication latency between Alibaba Cloud and your data center. VBRHealthyCheckLossRateThe packet loss rate between Alibaba Cloud and your data center. VBRInternetOutRateThe outbound bandwidth from Alibaba Cloud to your data center. VBRInternetInRateThe inbound bandwidth from your data center to Alibaba Cloud.
Threshold and Alert Level	Configure the alert condition, threshold, and level for the alert rule.

More operations

Actions	Description	Procedure
Modify a health check	Modify the source IP, destination IP, probe interval, or failure threshold of an existing health check. Note You cannot modify Switch Route. To change Switch Route, delete the health check and create a new one.	Log on to the CEN console. In the left-side navigation pane, click VBR Health Check. On the VBR Health Check page, select the region where the VBR instance is located. Find the health check that you want to modify and click Edit in the Actions column. In the Edit Health Check dialog box, modify the parameters and then click OK.
Delete a health check	Delete the health check when you no longer need to monitor the Express Connect circuit.	Log on to the CEN console. In the left-side navigation pane, click VBR Health Check. On the VBR Health Check page, select the region where the VBR instance is located. Find the health check that you want to delete and click Delete in the Actions column. In the Delete Healthcheck dialog box, click OK.

FAQ

Redundancy granularity with multiple VBRs

Express Connect circuit redundancy operates at the route entry level.

For example, if a Transit Router connects to VBR1 and VBR2 with these route entries:

When the health check of VBR1 fails, traffic destined for the 192.168.1.0/24 CIDR block is switched from VBR1 to the Express Connect circuit of VBR2.
When the health check of VBR2 fails, traffic destined for 192.168.1.0/24 is switched from VBR2 to the Express Connect circuit of VBR1. Traffic destined for 192.168.2.0/24 is not switched because there is no redundant path.

Destination CIDR block	Next hop	Associated network instance
192.168.1.0/24	VBR1 connection	VBR1
192.168.1.0/24	VBR2 connection	VBR2
192.168.2.0/24	VBR2 connection	VBR2

What happens if all VBR health checks fail?

For traffic from Alibaba Cloud to your data center, traffic is forwarded through the circuit of the last VBR whose health check failed.

If the last VBR's health check fails but the circuit is actually healthy, available bandwidth is reduced because traffic flows over only one circuit.
If the last VBR's health check fails and the circuit is also down, traffic is interrupted.

The last VBR is the one whose health check fails last. For example, if a Transit Router connects to VBR1, VBR2, and VBR3, and VBR1 and VBR2 fail before VBR3, all traffic is forwarded through VBR3's Express Connect circuit.

Destination CIDR block	Next hop	Associated network instance
192.168.1.0/24	VBR1 connection	VBR1
192.168.1.0/24	VBR2 connection	VBR2
192.168.1.0/24	VBR3 connection	VBR3

The impact on traffic from your data center to Alibaba Cloud depends on your network configurations.

Route switchover when all health checks fail

A route switchover occurs only when circuit connectivity status changes (healthy to unhealthy or vice versa).

Impact of deleting a health check

Deleting a health check in the CEN console does not cause route flapping. The system assumes the circuit is healthy and continues forwarding traffic based on the route table.

However, if the circuit is actually down, traffic is interrupted.
If you delete a health check in your data center, the impact depends on your network configuration.

Cloud Enterprise Network:Configure VBR health checks