Microsoft Network Load Balancing not working as expected

I wish to have a failover cluster for an IIS site in my domain.
I have configured the cluster on port 80, however only once the network of that specific node is down will the cluster detect that node is down.
If I stop the site through IIS manager that node is still considered healthy.
What am I doing wrong? Is this what do the product supposed to do? If not what other product can help me?