Virtualization server uses the hypervisor technology in its implementation. Hypervisor is one of the virtualization techniques. Where this technique runs several operating systems together in one host. Cloud computing is a combination of the use of internet-based computer technology. The Open source Proxmox VE (Virtual Environment) is a virtual machine operating system. Where virtual machines are built from the Debian Linux operating system, with the modified RHEL kernel. A firewall is a system designed to prevent attacks on the network. Firewalls can be software or hardware that filters network traffic. Proxmox VE Firewall provides a way to protect network infrastructure. In Proxmox VE firewall allows setting rules for all hosts in a cluster or for virtual machines. In this study, the performance of the firewall from the server virtualization using ProxmoxVE will be examined. This study is intended to determine the performance of the firewall default from Proxmox VE. Firewall testing is done by creating filtering rules in the Proxmox VE cloud server. The results of this study will provide an analysis of the performance of the Proxmox VE firewall that runs on cloud servers. The analysis presents that iptables firewall rules can be applied to cloud servers.