# What is a Virtual Firewall?

> A virtual firewall is software that performs firewall policy enforcement inside a virtualized infrastructure rather than on a dedicated physical appliance.

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## Content

It may run as a virtual machine, attach to a virtual switch or hypervisor, or be implemented by a virtualization platform to inspect traffic entering, leaving, or moving among virtual workloads.

Placement determines which paths the firewall can observe. Traffic between virtual machines on one host may never cross a physical firewall, while traffic routed through a virtual appliance may require deliberate service insertion. Policy should follow workload identity and approved communication needs when workloads migrate, scale, or receive new addresses.

### Key points

- **Deployment models:** A virtual appliance can protect a subnet or gateway path, while hypervisor- or switch-integrated enforcement can apply rules closer to individual virtual interfaces.
- **Operations:** Control images, software updates, policy templates, administrative interfaces, logs, and lifecycle automation with the same rigor as physical firewalls.
- **Capacity and resilience:** Validate throughput, connection state, inspection cost, failover, and the effect of host or control-plane failure; software deployment does not remove resource limits.
- **Important limitation:** “Virtual” describes implementation, not inspection quality or isolation strength. A bypass path, compromised virtualization layer, misplaced instance, or inconsistent policy can leave workload traffic unprotected.

### Related terms

[Firewall](<https://yellowcube.eu/glossary/firewall/>) · [Distributed firewall](<https://yellowcube.eu/glossary/distributed-firewall/>) · [Cloud firewall](<https://yellowcube.eu/glossary/cloud-firewall/>) · [Network segmentation](<https://yellowcube.eu/glossary/network-segmentation/>) · [Virtualization security](<https://yellowcube.eu/glossary/virtualization-security/>)

### Sources

[NIST SP 800-125B: Secure Virtual Network Configuration for VM Protection](https://csrc.nist.gov/pubs/sp/800/125/b/final) · [NIST SP 800-41 Rev. 1: Guidelines on Firewalls and Firewall Policy](https://csrc.nist.gov/pubs/sp/800/41/r1/final)

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