QEMU can simulate several network cards (e.g. PCI or ISA cards on the PC target) and can connect them to a network backend on the host or an emulated hub. The various host network backends can either be used to connect the NIC of the guest to a real network (e.g. by using a TAP devices or the non-privileged user mode network stack), or to other guest instances running in another QEMU process (e.g. by using the socket host network backend).
Using TAP network interfaces
This is the standard way to connect QEMU to a real network. QEMU adds a
virtual network device on your host (called
tapN), and you can then
configure it as if it was a real ethernet card.
As an example, you can download the
and copy the script
/etc and configure properly
sudo so that the command
ifconfig contained in
be executed as root. You must verify that your host kernel supports the
TAP network interfaces: the device
/dev/net/tun must be present.
See Invocation to have examples of command lines using the TAP network interfaces.
There is a virtual ethernet driver for Windows 2000/XP systems, called TAP-Win32. But it is not included in standard QEMU for Windows, so you will need to get it separately. It is part of OpenVPN package, so download OpenVPN from : https://openvpn.net/.
Using the user mode network stack
By using the option
-net user (default configuration if no
option is specified), QEMU uses a completely user mode network stack
(you don’t need root privilege to use the virtual network). The virtual
network configuration is the following:
guest (10.0.2.15) <------> Firewall/DHCP server <-----> Internet | (10.0.2.2) | ----> DNS server (10.0.2.3) | ----> SMB server (10.0.2.4)
The QEMU VM behaves as if it was behind a firewall which blocks all incoming connections. You can use a DHCP client to automatically configure the network in the QEMU VM. The DHCP server assign addresses to the hosts starting from 10.0.2.15.
In order to check that the user mode network is working, you can ping the address 10.0.2.2 and verify that you got an address in the range 10.0.2.x from the QEMU virtual DHCP server.
Note that ICMP traffic in general does not work with user mode
ping, aka. ICMP echo, to the local router (10.0.2.2)
shall work, however. If you’re using QEMU on Linux >= 3.0, it can use
unprivileged ICMP ping sockets to allow
ping to the Internet. The
host admin has to set the ping_group_range in order to grant access to
those sockets. To allow ping for GID 100 (usually users group):
echo 100 100 > /proc/sys/net/ipv4/ping_group_range
When using the built-in TFTP server, the router is also the TFTP server.
When using the
'-netdev user,hostfwd=...' option, TCP or UDP
connections can be redirected from the host to the guest. It allows for
example to redirect X11, telnet or SSH connections.
QEMU can simulate several hubs. A hub can be thought of as a virtual
connection between several network devices. These devices can be for
example QEMU virtual ethernet cards or virtual Host ethernet devices
(TAP devices). You can connect guest NICs or host network backends to
such a hub using the
-nic hubport options. The legacy
-net option also
connects the given device to the emulated hub with ID 0 (i.e. the
default hub) unless you specify a netdev with
Connecting emulated networks between QEMU instances
-netdev socket (or
-nic socket or
option, it is possible to create emulated networks that span several
QEMU instances. See the description of the
-netdev socket option in
Invocation to have a basic