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Ethernet-over-USB network

Basic configuration

Specifically to V2+. When combined with configuring a DNS server, FTP, or SMB (for example), this is a powerful way to extend the capabilities of PiKVM.

USB limitations

Each emulated USB device consumes a limited hardware resource called endpoints.

Short info: by default, you can add only one additional USB device.

To get more information about the endpoints, add more devices, and flexibly manage the configuration on the fly, see here.

  1. Edit /etc/kvmd/override.yaml and add these lines:

    otg:
    devices:
        ethernet:
            enabled: true
            driver: ecm
            host_mac: 48:6f:73:74:50:43
            kvm_mac: 42:61:64:55:53:42

    The host_mac address will be used on the server's network interface. The kvm_mac means the address that will be assigned to the local interface on the PiKVM. The KVM interface will be called usb0network interface. If the host_mac or kvm_mac is not specified, a random value will be used. The driver parameter means the protocol that will be used for the USB network. The default value is ecm so it can be passed it this example. Other possible values are eem, ncm, rndis and rndis5.

    Driver compatibility:

    Driver Operating System
    ecm Linux
    macOS
    eem Linux
    rndis5 Windows XP to Windows 71
    Linux > 2.6.13
    rndis Windows 7 and later2
    Linux > 2.6.13
    ncm Windows 10 and later
    Linux > 2.6.37
    macOS

    1: Manual driver installation is required. Download RNDIS 5 Windows
    2: Automatic driver installation since kvmd-3.53

  2. To automatically configure the USB network on the server recommended using the service kvmd-otgnet. It configures the firewall, assigns an address to the local PiKVM interface usb0 and starts DHCP so the managed server can get the IPv4 address. By default, the address 172.30.30.0/24 to interface usb0 will be assigned. One of the other addresses from the network 172.30.30.0/24 will be assigned to the server when it requests it via DHCP. For security reasons, all incoming connections from the server to the PiKVM side are blocked (except for ICMP and UDP port 67 which is used for DHCP). If you want to allow access from the server to the PiKVM interface, then you need to add ports 80 and 443 to the whitelist using /etc/kvmd/override.yaml file like this:

    otgnet:
    firewall:
        allow_tcp: [80, 443]

    To view other available configuration parameters, use the command kvmd -m.

  3. To enable the service, use the command systemctl enable kvmd-otgnet.

  4. Perform reboot.

Routing via PiKVM

By default, kvmd-otgnet will configure network connection between PiKVM and the server host only. The server host will not be able to reach other hosts beyond PiKVM. If the full network access is required from the server host through the USB-Ethernet feature (access all hosts PiKVM can access), additional settings are needed in /etc/kvmd/override.yaml.

  1. Run echo "net.ipv4.ip_forward = 1" > /etc/sysctl.d/99-kvmd-extra.conf.

  2. Add network interface to forward requests to (default gateway) by adding a line forward_iface: <interface name> under firewall:. Typically it would be eth0 if the built-in ethernet port is used::

    otgnet:
    firewall:
        forward_iface: eth0

  3. Add DNS server to provide host name resolution service. For example, adding 8.8.8.8 as DNS server requires addition of dnsmasq dhcp options. This can be done by adding following lines to /etc/kvmd/override.yaml:

    otgnet:
    commands:
        post_start_cmd_append:
        - "--dhcp-option=6,8.8.8.8"

  4. Combining above two together::

    otgnet:
    firewall:
        forward_iface: eth0
    commands:
        post_start_cmd_append:
        - "--dhcp-option=6,8.8.8.8"
    5. To enable internet access for the server host, add the following to the otgnet configuration:: 

     otgnet:
    iface:
        net: 10.65.0.0/28
    The 'net' parameter defines the network address range of the usb0 network. The server host will automatically receive an IP address within this network including the DNS servers defined under 'post_start_cmd_append'. Note: This network should not be same as the network PiKVM is connected to.

  5. Don't forget to reboot.

An example of what the config would look like for a server host that can access PiKVM and has internet access: 
otgnet:
    firewall:
        allow_tcp: [80, 443]
        forward_iface: wlan0
    commands:
        post_start_cmd_append:
            - "--dhcp-option=6,1.1.1.1,1.0.0.1"
    iface:
        ip_cmd:
            - /usr/bin/ip
        net: 10.65.0.0/28

Working with Windows Computers

This has been proven to work with Windows:

  1. Set the driver type to rndis (see above).

  2. Download this driver on the Windows machine and unzip it somewhere.

  3. Open the devices manager:
    grafik

  4. Select Properties of the Composite KVM Device:
    grafik

  5. Select the RNDIS Device and click properties:
    grafik

  6. Switch to the Driver tab and then click Update driver.

  7. Click Browse my computer for driver software:
    grafik

  8. Click Let me pick from a list of available drivers on my Computer:
    grafik

  9. From the list of available hardware types, scroll down and select Network adapters, then click Next:
    grafik

  10. Click Have disk:
    grafik

  11. Click Browse, navigate to the folder where you've stored the driver and select the RNDIS.inf, press Open and then OK:
    grafik

  12. Select Acer Netchip RNDIS/Ethernet Gadget and click Next:
    grafik

  13. Dismiss the warning about non-compatible drivers by clicking Yes:
    grafik

  14. You're done - the device should now be recognized:
    grafik

  15. Verify the card is working by pinging your PiKVM in a console: ping 172.30.30.1:
    grafik