I've installed qemu, and if I tell it to use -user-net, things work fine. I can ping www.yahoo.com
and get a response.
I'm trying to get it to talk to my tun device so that I can see my local network, and I can't get this to work. I've turned on ip forwarding (/proc/sys/net/ipv4/ip_forward) and NAT on the host, and the network looks like this:
tun gateway on host: 192.168.1.200
When I ping the gateway from the guest, the host's /var/log/messages records the packets as martians. When I ping the host directly from the guest, or viceversa, I get "icmp_seq=* Destination Host Unreachable".