What's the biggest gap in terms of visibility of a network infrastructure today? The first one that comes to mind is the visibility into your network connectivity in the Cloud, because most of that is going through, if not all of it is going through the public internet. A lot of companies rely on things like ping testing and stuff like that to see what response time is to SalesForce.com and stuff. How's that going to point you towards diagnostics and triage. You need tools that can give you visibility into your Cloud connectivity.
Another area that can be a potential gap is in the virtual network elements and your own infrastructure. A number of years ago the network ended at the top of rack switch, or the end of row switch, it doesn't anymore. Now you have hypervisors with network traffic going on inside them. Virtual switches forwarding traffic between VMs on a single host that never hits a physical network interface. A lot of monitoring vendors have done a lot of work to provide visibility into that traffic that never hits the physical network interface.
To some extent those issues have been solved, but not in all cases. For instance, now on those hypervisor hosts you might have a load balancer, or a firewall, or a SIP gateway, or intrusion prevention gateway. Those used to be appliances that you could monitor traffic coming in and out of, not anymore, they're in the hypervisor host and they may migrate with whatever work load they're serving. You need visibility into those virtual elements, the performance networks coming out of them, the health and availability of them but also is traffic being forwarded to them like it should since it's now virtual.
Are you service chaining a firewall service and a load balancing service to the workloads like your policy dictates? That's a big gap, that's an operational issue that hasn't been fully solved and as enterprises start to move away from a static appliance based layer 4-7s services world to one that is a mix of the two. You need operation tools to make sure that those gaps don't emerge.