Qemu networking - what's the secret?

Question

Yesterday I installed qemu with kqemu, and Win98 as the guest OS. Everything went as described in the wiki page and other docs, and it boots with no problems. W98 gets ip address 10.0.2.15, and I can access the host i.e. Arch on 10.0.2.2. However, as I understand it, this default setup should also give W98 internet access, but it doesn't.
Now before I go messing with tun/tap and the qemu-ifup script, can anyone tell me anything about this? Should the guest be networked by default? Have I missed something? :?

Answer 1

tomk wrote:
Yesterday I installed qemu with kqemu, and Win98 as the guest OS. Everything went as described in the wiki page and other docs, and it boots with no problems. W98 gets ip address 10.0.2.15, and I can access the host i.e. Arch on 10.0.2.2. However, as I understand it, this default setup should also give W98 internet access, but it doesn't.
Now before I go messing with tun/tap and the qemu-ifup script, can anyone tell me anything about this? Should the guest be networked by default? Have I missed something? :?
Before I begin: the user-net enabled internet access here without problems, but note that only regular tcp and udp stuff works, so no pings.
Ok, with the tuntap method, you need to know some stuff about networking to make it work.
First, here is my qemu-ifup script:
#!/bin/sh
if [ "$2" = "" ]; then
sudo "$0" "$1" "x" || exit 1
else
ifconfig $1 192.168.50.2 up || exit 1
/etc/rc.d/dhcpd restart || exit 1
fi
Of course, for this to work you have to add a sudo nopasswd rule. You may also need dhcp to be configured properly if you don't want to set W98's network settings manually. Then you have to add a nat rule to enable internet access from the virtual machine:
iptables -t nat -A POSTROUTING -s 192.168.50.0/24 -o ppp0 -j MASQUERADE
assuming ppp0 is your internet interface. Then just enable ip forwarding and you're done:
echo 1 > /proc/sys/net/ipv4/ip_forward