Network isolation and security

Applies to: Windows Server 2022, Windows Server 2019, Windows Server 2016

Isolation with network namespaces

Each container endpoint is placed in its own network namespace. The management host virtual network adapter and host network stack are located in the default network namespace. To enforce network isolation between containers on the same host, a network namespace is created for each Windows Server container and containers run under Hyper-V isolation into which the network adapter for the container is installed. Windows Server containers use a host virtual network adapter to attach to the virtual switch. Hyper-V isolation uses a synthetic VM network adapter (not exposed to the utility VM) to attach to the virtual switch.

Hyper-V isolation with a synthetic VM network adapter

Run the following Powershell cmdlet to get all network compartments in the protocol stack:


Network security

Depending on which container and network driver is used, port ACLs are enforced by a combination of the Windows Firewall and Azure Virtual Filtering Platform (VFP).

Windows Server containers

The following values use the Windows hosts' firewall (enlightened with network namespaces) as well as VFP:

  • Default Outbound: ALLOW ALL
  • Default Inbound: ALLOW ALL (TCP, UDP, ICMP, IGMP) unsolicited network traffic
    • DENY ALL other network traffic not from these protocols


Prior to Windows Server version 1709 and Windows 10 Fall Creators Update, the default inbound rule was DENY all. Users running these older releases can create inbound ALLOW rules with docker run -p (port forwarding).

Hyper-V isolation

Containers running in Hyper-V isolation have their own isolated kernel, and therefore, run their own instance of Windows Firewall with the following configuration:

  • Default ALLOW ALL in both Windows Firewall (running in the utility VM) and VFP.

Hyper-V isolation with firewall

Kubernetes pods

In a Kubernetes pod, an infrastructure container is first created to which an endpoint is attached. Containers that belong to the same pod, including infrastructure and worker containers, share a common network namespace (such as the same IP and port space).

Kubernetes pods networking

Customizing default port ACLs

If you want to modify the default port ACLs, review the Host Networking Service topic before changing the ports. You'll need to update policies inside the following components:


For Hyper-V isolation in Transparent and NAT mode, currently you can't reconfigure the default port ACLs, which is reflected by an "X" in the table below:

Network driver Windows Server containers Hyper-V isolation
Transparent Windows Firewall X
NAT Windows Firewall X
L2Bridge Both VFP
L2Tunnel Both VFP
Overlay Both VFP