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            <p>It is said that a <a href="http://fabrice.bellard.free.fr/qemu/">qemu</a> guest operating system can talk to it's host operating system through the network with the help something called <a href="http://vtun.sourceforge.net/tun/faq.html">tun/tap</a>, something which I am ashamed to say I have never heard of before.</p>
            <p>Configuring network cards, ppp or routing tables has never been my strong point, so TUN/TAP isn't something that I approached with eagerness. But having <a href="721.html">successfuly setup qemu</a>, networking is sorely needed if it is to be made full use of. It's just too bad that there isn't anything really usefull on <a href="https://www.google.com">google</a> about this topic.</p>
            <p>After struggling unsuccessfully to asign an 192.168.x.x IP to the guest operating system (the NIC on the host system has such an IP), I decided to rever to the default 172.20.x.x ip (which is in fact asigned by DHCP). The original qemu-ifup script was also reverted to. It assigned 172.20.0.1 to the tun0 interface on the host.</p>
            <p>I can open a socket connection in 5 different programming languages but ask me to set up a NAT and I would struggle. Having said that I still needed to enable NAT so that the guest system could access the outside world. Fortunately, I can type in :</p>
            <p>iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE</p>
            <p>and</p>
            <p>echo 1 &gt; /proc/sys/net/ipv4/ip_forward</p>
            <p>by rote. There is still another issue to be addressed; I have a webserver on the host system with about a dozen IP virtual hosted sites. Since all the IPs are private network IPs they do not have DNS entries, that meant the hosts file on the guest system had to be edited. That's only a part of the solution becuase it's not practical to create a dozen virtual NICs every host entries, all host entries point to the same IP. That calls for a another set of iptable rules.</p>
            <p>First I try adding rules to the PREROUTING chain, then after tearing my hair tried the same with the OUTPUT chain still without success, finally I jumped to the wrong conclusion that tun0 is not too concerned about obeying iptables rules. That was proved wrong by the simple rule</p>
            <p>iptables -A INPUT -i tun0 -j DROP</p>
            <p>After struggling with it a little longer, I finally realised that had I chosen to set up a few virtual nics I would have finished it in less than 5 minutes. This is of course the down side of being a geek.</p>
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Qemu and networking

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            <p>Just downloaded 0.7.0 of <a href="http://fabrice.bellard.free.fr/qemu/">qemu</a>. Looks like there have been two releases since the last time I tried it out. Improvements include a step towards <a href="https://www.apple.com/macosx/">Mac OS X</a> support.</p>
            <p>Last time around I didn't have much success with it partly due to a lack of patience on my part. The documentation being very cryptic didn't help either. This time around, I found that there is a running commentary on qemu on varius sites and more importantly <a href="http://www.advantageplayer.com/blackjack/forums/bj-tech/webbbs.cgi?noframes;read=2043">answers!</a></p>
            <p>So unlike the last time around I had more success in installing the guest operating system. This is the command I used at first:</p>
            <p>qemu -boot d -cdrom /dev/hdc -hda hd.img</p>
            <p>Unfortunately it turned out to be painfully slow. So I tried copying the entire CD into <a href="000527.html">memory</a></p>
            <p>dd if=/dev/hdc of=/dev/shm/boot.img</p>
            <p>Of course you need to have a lot of memory if you take this approach, it only lead to a small increase in speed, but it was enough. Once the installation was completed, this is how I boot the system:</p>
            <p>qemu -boot c -hda hd.img</p>
            <p>Now I feel like ordering a copy of OS X Tiger and trying that out as the guest system.</p>
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Monthly Archives for 2005 05

Qemu and networking

Qemu