I can not overstate how huge this is. MongoDB Inc. did a fantastic job on it. Not only does it support the classic client address matching, it supports an array of these with matching on the server IP/host also. This means supporting multiple IP segments with a single user is very easy. By extension, I could see a future where you could even limit some actions by range – allowing dev/load test to drop collections, but production apps would not be allowed to. While they should have separate users, I regularly see clients who have one password everywhere. That extension would save them from unplanned outages due to human errors of connecting to the wrong thing.