Networking

gVisor implements its own network stack called netstack. All aspects of the network stack are handled inside the Sentry — including TCP connection state, control messages, and packet assembly — keeping it isolated from the host network stack. Data link layer packets are written directly to the virtual device inside the network namespace setup by Docker or Kubernetes.

The IP address and routes configured for the device are transferred inside the sandbox. The loopback device runs exclusively inside the sandbox and does not use the host. You can inspect them by running:

docker run --rm --runtime=runsc alpine ip addr

Network passthrough

For high-performance networking applications, you may choose to disable the user space network stack and instead use the host network stack, including the loopback. Note that this mode decreases the isolation to the host.

Add the following runtimeArgs to your Docker configuration (/etc/docker/daemon.json) and restart the Docker daemon:

{
    "runtimes": {
        "runsc": {
            "path": "/usr/local/bin/runsc",
            "runtimeArgs": [
                "--network=host"
            ]
       }
    }
}

Disabling external networking

To completely isolate the host and network from the sandbox, external networking can be disabled. The sandbox will still contain a loopback provided by netstack.

Add the following runtimeArgs to your Docker configuration (/etc/docker/daemon.json) and restart the Docker daemon:

{
    "runtimes": {
        "runsc": {
            "path": "/usr/local/bin/runsc",
            "runtimeArgs": [
                "--network=none"
            ]
       }
    }
}

Disable GSO

If your Linux is older than 4.14.77+ , you can disable Generic Segmentation Offload (GSO) to run with a kernel that is newer than 3.17. Add the --gso=false flag to your Docker runtime configuration (/etc/docker/daemon.json) and restart the Docker daemon:

Note: Network performance, especially for large payloads, will be greatly reduced.

{
    "runtimes": {
        "runsc": {
            "path": "/usr/local/bin/runsc",
            "runtimeArgs": [
                "--gso=false"
            ]
       }
    }
}