Gentoo QEMU/KVM ethernet bridging nano HOWTO

Qemu could use tun/tap to emulate bridged network, so the guest could have a real ip as host. ie:

[code]qemu -net nic -net tap[/code]

or

[code]kvm -net nic -net tap[/code]

Under gentoo, in order to use that, we have to:

* kernel requirements:

CONFIG_BRIDGE, CONFIG_TUN must be included (y/m) CONFIG_KVM_INTEL/CONFIG_KVM_AMD must be selected in order to use kvm

CONFIG_IP_PNP and CONFIG_ROOT_NFS must be included to use nfsroot/diskless mounted filesystem. Host side NIC driver must also be compiled into kernel (y).

* user space application:

bridge-utils, qemu/kvm

Networking interface layout:

br0: bridge interface, binded with real IP address for network access. eth0: interface of br0, no IP. tapX: interface of guest, no IP.

NOTE: switch interfaces don't have an IP address.

Network configuration in gentoo:

*) make sure NetworkManager/dhcdbd is not started, network interface must not be managed by NetworkManager. ie:

[code]

$ cd /etc/init.d/ $ ln -s net.lo net.eth0 $ ln -s net.lo net.br0 $ rc-update add net.eth0 default $ rc-update add net.br0 default

[/code]

*) /etc/conf.d/net configration, ie:

[code]

bridge_br0="eth0" config_br0=("dhcp") config_eth0=("null")

[/code]

You have to insert some modules if neccessary like:

[code]

$ modprobe tun kvm_amd

[/code]

Start using qemu/kvm:

[code]

$ kvm -kernel bzImage -append "root=/dev/nfs rw nfsroot=192.168.2.xxx:/home/gentoo-x86 ip=on" -net nic,model=e1000 -net tap

[/code]

Note: kvm have it's own network startup/stop scripts /etc/kvm/kvm-if{up,down} in gentoo, if you're using qemu, you have to write your own /etc/qemu-if{up,down} scripts, just copying /etc/kvm/kvm-if{up,down} it's essential.

.refs:

http://www.linuxfoundation.org/en/Net:Bridge gentoo's /etc/conf.d/net.example