UbuntuNetworking
Setting up NAT with KVM in Ubuntu
Normally, the best way to do guest networking is by setting up a bridge. However, if you use a wireless card, are frequently switching network interfaces or using VPN, or for other reason want to do NAT, then this outlines the easiest way to set it up with Ubuntu. The setup here is very similar to what libvirt uses for QEMU networking.
Install Dependencies
sudo apt-get install bridge-utils dnsmasq
Check Kernel Modules
Make sure that all of the following modules are around: either built in to the kernel or loadable. If you are running a plain distribution kernel, you should have all of these around without doing anything extra.
# lsmod
Module Size Used by
tun 15616 0
bridge 64104 0
llc 11504 1 bridge
xt_state 5248 1
ipt_MASQUERADE 6720 1
iptable_nat 10512 1
nf_nat 24344 2 ipt_MASQUERADE,iptable_nat
nf_conntrack_ipv4 21776 3 iptable_nat
nf_conntrack 76688 5 xt_state,ipt_MASQUERADE,iptable_nat,nf_nat,nf_conntrack_ipv4
Enabling ip forwarding
Add the following line to the bottom of /etc/sysctl.conf
net.ipv4.ip_forward=1
Configuring a bridge
Add the following to the bottom of /etc/network/interfaces
auto br0
iface br0 inet static
address 10.0.1.1
netmask 255.255.255.0
network 10.0.1.0
bridge_stp off
bridge_maxwait 5
bridge_ports none
pre-up iptables-restore < /etc/iptables.up.rules
Installing config files
- Copy dnsmasq.conf to
/ec/dnsmasq.conf
- Copy iptables.up.rules to
/etc/iptables.up.rules
- Copy qemu-ifup to
/etc/qemu-ifup and change permissions to 755