Networking on Docker Desktop

This page explains how Docker Desktop routes network traffic and file I/O between containers, the VM, and the host, and how this behavior is visible to firewalls and endpoint protection tools.

Overview

Docker Desktop runs the Docker Engine inside a lightweight Linux virtual machine (VM). Depending on your system configuration and operating system, Docker Desktop routes network and file operations between the Docker VM and the host using different backend components.

Backend components and responsibilities

The backend acts as:

• Network proxy: Translates traffic between the host and Linux VM.
  • On Windows and Mac, this is handled by the com.docker.backend process.
  • On Linux, the qemu process performs this function.
• File server: Handles file access from containers to the host filesystem.
  • When using gRPC FUSE, the backend performs the file sharing.
  • When using virtiofs, osxfs, or krun, file access is handled by those respective daemons rather than the backend process.
• Control plane: Manages Docker API calls, port forwarding, and proxy configuration.

The following table summarizes typical setups in more detail:

How containers connect to the internet

Each Linux container in Docker Desktop runs inside a small virtual network managed by Docker and every container is attached to a Docker-managed network and receives its own internal IP address. You can view and these networks with docker network ls, docker network create, and docker network inspect. They are managed by the daemon.json.

When a container initiates a network request, for example with apt-get update or docker pull:

• The container’s eth0 interface connects to a virtual bridge (docker0) inside the VM.
• Outbound traffic from the container is sent through Network Address Translation (NAT) using a virtual adapter (typically with an internal IP such as 192.168.65.3). You can view or change this with the Docker Desktop settings.
• The traffic is transferred to the host system over a shared-memory channel rather than through a traditional virtual network interface. This approach ensures reliable communication and avoids conflicts with host-level network adapters or firewall configurations.
• On the host, Docker Desktop’s backend process receives the traffic and creates standard TCP/IP connections using the same networking APIs as other applications.

All outbound container network traffic originates from the com.docker.backend process. Firewalls, VPNs, and security tools, like Crowdstrike, see traffic coming from this process — not from a VM or unknown source so firewall and endpoint security software can apply rules directly to com.docker.backend.

How exposed ports work

When you publish a container port using the -p or --publish flag, Docker Desktop makes that container port accessible from your host system or local network.

For example, with docker run -p 80:80 nginx:

• Docker Desktop's backend process listens on the specified host port, in this case, port 80.
• When an application such as a web browser connects to that port, Docker Desktop forwards the connection into the Linux VM where the container is running over a shared-memory channel.
• Inside the VM, the connection is routed to the container’s internal IP address and port, for example 172.17.0.2:80.
• The container responds through the same path, so you can access it from your host just like any other local service.

By default, docker run -p listens on all network interfaces (0.0.0.0), but you can restrict it to a specific address, such as 127.0.0.1 (localhost) or a particular network adapter.

Host firewalls can permit or deny inbound connections by filtering on com.docker.backend.

Using Docker Desktop with a proxy

Docker Desktop can use your system’s default proxy settings or custom settings that you configure with Docker Desktop's proxy setting. All proxy traffic passes through com.docker.backend.exe.

When a proxy is enabled:

• The backend process forwards the network requests, for example docker pull, through an internal proxy at http.docker.internal:3128.
• The internal proxy then connects either directly to the internet or through your upstream proxy, depending on your configuration and adding authentication if necessary.
• Docker Desktop then downloads the requested images or data through the proxy as usual.

Note that:

• The proxy honors system or manual proxy configuration.
• On Windows, Basic, NTLM, and Kerberos authentication is supported.
• For Mac, NTLM/Kerberos is not supported natively. Run a local proxy on localhost as a workaround.
• CLI plugins and other tools that use the Docker API directly must be configured separately with the HTTP_PROXY, HTTPS_PROXY, and NO_PROXY environment variables.

Firewalls and endpoint visibility

To restrict VM or container networking apply rules to com.docker.backend.exe (Windows) com.docker.backend (Mac) or qemu (Linux) as all VM networking is funneled through these processes.

Use Windows Defender Firewall or enterprise endpoint firewalls for control. This enables traffic inspection and restriction at the host level without modifying the Docker Engine.

Crowdstrike and similar tools can observe all traffic and file access that passes through the backend process.