Why Do Many IP Addresses Accessing the Backend ECSs Associated with a Load Balancer Start with 100.125?

This issue is caused by the health checks.

In addition to forwarding access requests to the backend ECSs using the internal IP addresses of system servers, ELB performs health checks for the ECSs to monitor their status. When forwarding access requests or initiating health check requests, the ELB system translates source IP addresses contained in the requests into IP addresses starting with 100.125, such as

To make your external services available, ensure that the security group containing the ECSs allows traffic from these IP addresses.

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