QEMU can simulate several network cards (PCI or ISA cards on the PC target) and can connect them to an arbitrary number of Virtual Local Area Networks (VLANs). Host TAP devices can be connected to any QEMU VLAN. VLAN can be connected between separate instances of QEMU to simulate large networks. For simpler usage, a non privileged user mode network stack can replace the TAP device to have a basic network connection.
QEMU simulates several VLANs. A VLAN can be symbolised 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).
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 linux-test-xxx.tar.gz
archive and copy the script qemu-ifup in /etc and
sudo so that the command
contained in qemu-ifup can 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 sec_invocation to have examples of command lines using the TAP network interfaces.
Using the user mode network stack¶
By using the option -net user (default configuration if no -net 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:
QEMU VLAN <------> 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 networking.
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.