An enforcement module receives a DNS-based rule of a segmentation policy that controls access of a managed workload to workloads in a DNS domain in which the IP addresses of the workloads associated with a domain name are resolved by a DNS server. When the managed workload makes a connection request to the workload associated with the domain name, the enforcement module snoops on a DNS response from the DNS server to learn the IP address of the workload associated with the domain name. If a domain name of the DNS domain is in a whitelist of domain names permitted by the DNS-based rule, the enforcement module adds the learned IP address to a whitelist of IP addresses and configures a firewall associated with the managed workload to permit connections to the IP addresses in the whitelist.