“Crunchy outer shell, soft center is bad”
In general terms, implementing defense-in-depth strategies is always a sensible practice. The concept in which multiple layers of security controls (defense) are placed throughout an information technology (IT) system. Its intent is to provide redundancy in the event a security control fails or a vulnerability is exploited.
Implementing a firewall on the network and host-based packet filters provides defense-in-depth layers to your infrastructure. In today’s landscape, the firewall aspect could be a service like ec2 security groups with host-based packet filters such as iptables, Windows Firewall (or WFAS). Although this can add additional complexity to deployment, that is not a reason to not implement it where appropriate.
The defense-in-depth concept is mostly regarded in terms of attack and compromise, however in ops it also safeguards us as everyone makes mistakes. Sometimes, we ourselves or our colleagues are the point of failure.
Strange as it may seem, people often make the mistake of disabling “rules” when something is not working and they cannot figure out why. The just checking test. This is always the first mistake. In real world operations these things do happen, whether it is a just checking mistake, an incorrect configuration or action, sometimes we make serious mistakes, to err is human.
In all these situations using a firewall/other and host-based packet filters comes to the fore:
The synopsis is that a practice of disabling rules was implemented, as it had always been the last line in debugging. It was a practice that had been done many times by the engineers in the organisation at the time with no “apparent” consequences in the past. This time differed in that the MSSQL server had a public interface added to allow for replication with the customer and SQL Slammer was in the wild.
If the MSSQL server had ip filtering enabled as well the situation would have been mitigated. Needless to say, it was the last time “Allow from all” debug strategy was ever implemented. However it is useful to note, that because this was done all the time, the engineer in question did not even tie the action of “Allow from all” and the network becoming unreachable together at the time, because the action previously had never resulted in the outcome that was experienced in this instance.
What is PKI? What uses it? Why is it important?
What is compliance and why do you need it?
What kinds of data can’t you store without it?
Eg, local vs cloud, the implications, etc