The MongoDB is a Linux running Ubuntu Trusty(14.04) on our LAN, and I am pretty sure there is NO firewall of any kind on it 
In the [URL]http://172.16.18.102/prometheus/targets[/URL] ) and find a lot of data in them, so I guess the 2 ports are open !!
But the Endpoint links of [url]http://localehost:9100/metrics[/url] for linux and the Endpoint link of [url]http://localhost:9090/prometheus/metrics[/url] for prometheus can NOT be reached 