QEMU’s user networking won’t do UDP out of the box, so I poked around online for a solution. What’s out on the web is a hodge-podge of tutorials, all of them different, and most of them for a non-current (read: not QEMU 0.8.0) release. This is a (equally poor) guide to get bridged networking working. FYI, my distro du jour is Ubuntu 5.10, and I hope to revise these instructions should the need arise to re-configure my setup.
First, check out How to install QEmu on Ubuntu Linux (Breezy) for some aptly named instructions.
From the tun/tap on ubuntu thread on Ubuntu Forums (probably not necessary?):
# apt-get install uml-utilities
# tunctl
From qemu 'networking howto':
# ifconfig eth0 down
# brctl addbr br0
# ifconfig eth0 0.0.0.0 promisc up
# ifconfig tun0 0.0.0.0 promisc up
# ifconfig br0 192.168.1.2 netmask 255.255.255.0 broadcast 192.168.1.255 up
# brctl stp br0 off
# brctl setfd br0 1
# brctl sethello br0 1
# brctl addif br0 eth0
# brctl addif br0 tun0
# route add default gw 192.168.1.1
From djw's qemu network bridge page, modify your /etc/qemu-ifup to something like:
#!/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
Finally, what they never tell you is how to start up QEMU. Little did I know that when you connect TAP to a VLAN, it doesn’t create the NIC for you. I wasted about a hour until I realized you need to append another -net nic. Here’s how I start QEMU:
qemu debian.img -kernel bzImage-2.6.14 -append "root=/dev/hda1" -net tap -net nic
Voila, mon ami. C’est tout!
Update: You’ll want to chmod 666 /dev/net/tun, and make sure you have the bridge-utils package.
Update 2: I have kernel config files for Linux 2.4.20, 2.6.11 (found these first two online), and 2.6.14. These build decently small kernels without modules that boot up in QEMU.