How can I create a virtual ethernet interface on a machine without a physical adapter?

Question

I have a Dell XPS 13 ultrabook which has a wifi nic, but no physical ethernet nic (wlan0, but no eth0). I need to create a virtual adapter for using Vagrant with NFS, but am finding that the typical ifup eth0:1... fails with ignoring unknown interface eth0:1=eth0:1. I also tried creating a virtual interface against wlan0, but received the same result.

How can I create a virtual interface on this machine with no physical interface?

Answer 1

Setting up a dummy interface

If you want to create network interfaces, but lack a physical NIC to back it, you can use the dummy link type. You can read more about them here: iproute2 Wikipedia page.

Creating eth10

To make this interface you'd first need to make sure that you have the dummy kernel module loaded. You can do this like so:

$ sudo lsmod | grep dummy
$ sudo modprobe dummy
$ sudo lsmod | grep dummy
dummy                  12960  0 

With the driver now loaded you can create what ever dummy network interfaces you like:

$ sudo ip link set name eth10 dev dummy0

And confirm it:

$ ip link show eth10
6: eth10: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default 
    link/ether c6:ad:af:42:80:45 brd ff:ff:ff:ff:ff:ff

Changing the MAC

You can then change the MAC address if you like:

$ sudo ifconfig eth10 hw ether 00:22:22:ff:ff:ff
$ ip link show eth10
6: eth10: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default 
    link/ether 00:22:22:ff:ff:ff brd ff:ff:ff:ff:ff:ff

Creating an alias

You can then create aliases on top of eth10.

$ sudo ip addr add 192.168.100.199/24 brd + dev eth10 label eth10:0

And confirm them like so:

$ ifconfig -a eth10
eth10: flags=130<BROADCAST,NOARP>  mtu 1500
        ether 00:22:22:ff:ff:ff  txqueuelen 0  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

$ ifconfig -a eth10:0
eth10:0: flags=130<BROADCAST,NOARP>  mtu 1500
        inet 192.168.100.199  netmask 255.255.255.0  broadcast 192.168.100.255
        ether 00:22:22:ff:ff:ff  txqueuelen 0  (Ethernet)

Or using ip:

$ ip a | grep -w inet
    inet 127.0.0.1/8 scope host lo
    inet 192.168.1.20/24 brd 192.168.1.255 scope global wlp3s0
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
    inet 192.168.100.199/24 brd 192.168.100.255 scope global eth10:0

Removing all this?

If you want to unwind all this you can run these commands to do so:

$ sudo ip addr del 192.168.100.199/24 brd + dev eth10 label eth10:0
$ sudo ip link delete eth10 type dummy
$ sudo rmmod dummy

References

• MiniTip: Setting IP Aliases under Fedora
• Linux Networking: Dummy Interfaces and Virtual Bridges
• ip-link man page
• iproute2 HOWTO
• iproute2 cheatsheet

Answer 2

You can create virtual interfaces using the iproute2 toolkit.

ip link add veth0 type veth peer name veth1

This will create 2 interfaces, veth0 and veth1. Think of them as 2 ends of a pipe. Any traffic sent into veth0 will come out veth1 and vice versa.

If you want the traffic to be routed, you can do:

sysctl -w net.ipv4.conf.veth0.forwarding=1

This will tell the kernel to forward traffic coming from veth0 (so use veth1 for the used endpoint).

Another option is to set up a bridge with veth0 and another interface. Then any traffic coming through the virtual interface will get routed out to the network as if your machine were simply acting as a switch.

There are many other things you can do with this traffic (masquerade it, redirect it, DNAT it, etc), but that depends on what you're trying to accomplish.

To tear it down:

ip link del veth0