Explanation

https://www.cisco.com/c/en/us/products/security/what-is-a-ddos-attack.html

Cisco Umbrella is a cloud-delivered security service that provides DNS-layer security, secure web gateway, firewall, cloud access security broker, and threat intelligence functions. It helps improve security visibility, detect compromised systems, and protect your users on and off the network by stopping threats over any port or protocol before they reach your network or endpoints1. One of the benefits of using Cisco Umbrella is that it can block threats before they launch, reducing response times, and delivering safe, secure internet with Umbrella's cloud tools2. By intercepting DNS requests and applying security policies, Umbrella can prevent malicious connections from being established, and mitigate attacks before the application connection occurs3. This can also reduce bandwidth costs and improve performance by filtering out unwanted traffic1. References: 1: The Essential Benefits of Cisco Umbrella 2: 5 Reasons to Try Cisco Umbrella Now 3: Why choose Cisco Umbrella for cybersecurity protection

Only in On-site (on-premises) and IaaS we (tenant) manage O/S (Operating System).