Using TUN/TAP networking with QEMU grant guest machines access to some or all networks reachable by the host machine. This also allows accessing services offered by guests machines from any other host.
To be able to use TUN/TAP network, instead of directly configuring the physical Ethernet network device — my Realtek 8169 Gigabit Ethernet, which in my computer it’s named eth1 –, we need to reconfigure the network in order to get a bridge device, named br0, with the physical Ethernet eth1 device attached to it. We can achieve this by editing /etc/network/interfaces to look like this:
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
#auto eth1
#iface eth1 inet static
auto br0
iface br0 inet static
address a.b.c.d
netmask 255.255.255.128
gateway v.w.x.y
bridge_ports eth1
bridge_fd 1
bridge_hello 1
bridge_stp off
The helper script /etc/qemu-ifup, which QEMU uses to bring up a TAP network interface used by the guest and bind it to the existing bridge br0, should look like this:
#!/bin/sh echo "Executing /etc/qemu-ifup" echo "Bringing up $1 for bridged mode..." sudo /sbin/ifconfig $1 0.0.0.0 promisc up echo "Adding $1 to br0..." sudo /usr/sbin/brctl addif br0 $1 sleep 2
To allow running QEMU as an unprivileged user, we need to edit /etc/sudoers in order to grant access for running /sbin/ifconfig and /usr/sbin/brctl. It’s recommended to edit that file using visudo. The file should could look like this:
# Cmnd alias specification
Cmnd_Alias QEMU=/sbin/ifconfig, \
/sbin/modprobe, \
/usr/sbin/brctl
# Defaults
Defaults !lecture,tty_tickets,!fqdn,rootpw
# User privilege specification
root ALL=(ALL) ALL
# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL
# Grant access to Cmnd_Alias to user jdoe
jdoe ALL=NOPASSWD:QEMU
Now, we can launch qemu from the command line:
XLIB_SKIP_ARGB_VISUALS=1 \ qemu -hda hda -cdrom *iso -boot d \ -m 512 -localtime -net nic,vlan=0 \ -net tap,ifname=tap0,script=/etc/qemu-ifup \ -kernel-kqemu
felipe-alfaro.com 
Hi,
I see lot of site for Qemu network interface it is a good article but only thing is my host disconnet the Main network.
Hi,
I see lot of site for Qemu network interface it is a good article. and i really reffer this one for network interfacing for qemu.
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How could I do this tun/tap startup script in Windows ?? It will be some that ??
echo..
./qemu script.bat …
etc. ..
Thanks.
XLIB_SKIP_ARGB_VISUALS=1 \
qemu -hda hda -cdrom *iso -boot d \
-m 512 -localtime -net nic,vlan=0 \
-net tap,ifname=tap0,script=/etc/qemu-ifup \
-kernel-kqemu
open /dev/kvm: No such file or directory
Could not initialize KVM, will disable KVM support
qemu: could not open disk image hda: No such file or directory
Help?
It looks like you don’t have KVM support installed. What distribution are you using?
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