How do you keep everything monitored?

Hi,

I Ops Manager in a Big datacenter and sometimes we have trouble to keep everything monitored. We use a lot of Zabbix and a private Workflow tool for CMDB but frequently we find switch's or router's that were added to the topology and are not monitored or added to the CMDB.. Of course this means flaws in change management process.

But how do you make compliance with this problem ? Network discovery tools like Netdisco ? Can you share you experience on this subject or recommend any good books and tools to take a look ?

We are working on making our process more strong and clear but i need to add some controls to make sure.