First, you need to make sure that the uml_utilities are installed on the host. You'll be needing the uml_net helper from that package.

You can either

• specify eth0 on the command line:

  eth0=tuntap,,,192.168.0.254
  

• hot-plug it into a running UML

  host% uml_mconsole umid config eth0=tuntap,,,192.168.0.254
  

  To hotplug anything, you need to figure out the UMID for the UML you want to communicate with. Replace the "umid" in the command line above with the umid of your UML.

In both cases, the actual device specification is the same.

Choose an IP address for the host end of the TUN/TAP device (192.168.0.254 in the examples above) that is usable on your network. It will be used on the host as the address of the TUN/TAP interface. If you use a 168.192.x.x or 10.x.x.x address, you may need to set up NAT on the host in order to communicate with the outside Internet.

Choose an IP address for the UML eth0 - the main constraint being that it must be different from the IP address you specified in the eth0=... description above.

Enabling the device is exactly the same as any other Linux machine, except you'll likely do by hand at first for UML:

UML# ifconfig eth0 192.168.0.253 up
* modprobe tun
* ifconfig tap0 192.168.0.252 netmask 255.255.255.255 up
* bash -c echo 1 > /proc/sys/net/ipv4/ip_forward
* route add -host 192.168.0.253 dev tap0
* bash -c echo 1 > /proc/sys/net/ipv4/conf/tap0/proxy_arp
* arp -Ds 192.168.0.253 eth0 pub

If you don't see the output above in your terminal, run dmesg, and you will see it. If there were any problems setting up the host, then error messages will also appear here.

At this point, you should be able to communicate with the host and the local network. To talk to the outside network, set a default route to the host end of the TUN/TAP device

UML# route add default gw 192.168.0.254