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You have an app named App1 that is installed on two Azure virtual machines named VM1 and VM2. Connections to App1 are managed by using an Azure Load Balancer.
The effective network security configurations for VM2 are shown in the following exhibit.

You discover that connections to App1 from 131.107.100.50 over TCP port 443 fail.
You verify that the Load Balancer rules are configured correctly.
You need to ensure that connections to App1 can be established successfully from
131.107.100.50 over TCP port 443.
Solution: You delete the BlockAllOther443 inbound security rule.
Does this meet the goal?
Correct Answer: A
The Load Balancer backend pool VMs may not be responding to the probes due to any of the following reasons:
- Load Balancer backend pool VM is unhealthy.
- Load Balancer backend pool VM is not listening on the probe port.
- Firewall, or a network security group is blocking the port on the Load Balancer backend pool VMs.
- Other misconfigurations in Load Balancer.
Note: Check if a Deny All network security groups rule on the NIC of the VM or the subnet that has a higher priority than the default rule that allows LB probes & traffic (network security groups must allow Load Balancer IP of 168.63.129.16).
Reference:
https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-troubleshoot-health-probe- status