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285 lines
11 KiB
285 lines
11 KiB
=============================================================================
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This HOWTO originally appeared on:
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http://lists.gnu.org/archive/html/qemu-devel/2004-10/msg00067.html
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=============================================================================
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Using VDE with Qemu HOWTO
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by Jim Brown
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5 Oct 2004
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Version 0.2
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-----------------------------------------------------------------------------
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Introduction
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Copyright
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What is qemu?
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What is VDE?
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Configuring and Installing VDE
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Installation
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vdeq & vdeqemu
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User-mode networking
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How to enable user-mode networking
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Firewall configuration
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Slirp (rootless) networking
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What is slirp networking?
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How to enable slirp networking?
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Setting up qemu
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How to set up the guest OS
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Credits
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-----------------------------------------------------------------------------
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Introduction
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Copyright
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Copyright (c) 2004 Jim Brown.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.2
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
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Texts. A copy of the license is available at http://www.gnu.org/licenses/fdl.txt
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What is qemu?
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Qemu is a FAST! processor emulator by Fabrice Bellard, available at
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http://fabrice.bellard.free.fr/qemu/. It is capable of emulationg the x86 and
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PowerPC processors with support for other processors on the way. The original
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purpose of qemu was to allow running x86-specific Linux applications, such as
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WINE or DosEmu, on non-x86 systems. However, qemu has expanded into becoming
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a full-fledged emulator. On the x86 side, it is capable of running Linux,
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MS-DOS, Windows 95/98/Me, Windows NT/2k, Windows XP, Solaris, OpenBSD, and
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FreeBSD. See http://fabrice.bellard.free.fr/qemu/ossupport.html for the full
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listing.
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This howto assumes that you have already installed and set up qemu.
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What is VDE?
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VDE is short for Virtual Distributed Ethernet. VDE, written by
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Renzo Davoli, is based off of uml_switch by Jeff Dike. It is available at
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http://sourceforge.net/projects/vde/. It has many uses, the main one providing
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support for networking with emulated computers. (Not just qemu, but support
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for user-mode linux and Bochs also exists). VDE must be set up and installed by
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root, but the programs which use it do not need root privligies.
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This howto will walk you through the simple process of installing
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VDE and setting up qemu to use it.
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-----------------------------------------------------------------------------
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Configuring and Installing VDE
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Installation
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You may obtain the source code at http://sourceforge.net/projects/vde/.
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The version of VDE which I used was 1.4.1, but this HOWTO should apply to all
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versions.
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Once you have downloaded the source code, extract it. I assume you
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will have extracted it to /space/vde. Go into that directory, and simply type
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"make" followed by "make install". Now you should have vde_switch in /usr/bin.
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vdeq & vdeqemu
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Now cd into the qemu directory. Type "make". This will build vdeq.
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Qemu on its own only supports full networking with tuntap, which requires
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root priviliges or an exposed /dev/net/tun. There is a -user-net option, but
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that is not as useful as full networking. In order for qemu to use VDE, it must
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be passed the file descriptor for a tun device. Futhermore the tun device itself
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must already be configured to use VDE. vdeq sets this up and passes it to qemu
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via the -tun-fd switch.
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There is no "make install". Instead, you just manually copy vdeq to
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/usr/bin. It might also be helpful to copy or link vdeq to vdeqemu. vdeq
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requires that the location of the qemu binary be passes to it as the first
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command line parameter, but vdeqemu only needs the options you want to pass to
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qemu. vdeqemu will locate the qemu binary itself (this requires that you install
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qemu system-wide or have the qemu directory in your PATH).
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For example if you have:
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vdeq qemu -hda /mnt/myimage -m 64 -boot a
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you can shorten this into
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vdeqemu -hda /mnt/myimage -m 64 -boot a
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-----------------------------------------------------------------------------
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User-mode Networking
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How to enable user-mode networking
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The following commands will need to be run as root:
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# vde_switch -tap tap0 -daemon
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If you need to run a sniffer, just in case you want to analyze the traffic,
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you can also run it like this:
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# vde_switch -hub -tap tap0 -daemon
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(The -hub option is not available for version 1.4.1 of VDE, you will need a
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later version. I don't know what the minimal version is but 1.5.1 does support
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this option.)
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Then you must run this:
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# ifconfig tap0 <ip>
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# chmod 755 /tmp/vde.ctl
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The vde_switch command will run VDE in the background. The -tap tap0
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parameter tells VDE to set up the device tap0 using tuntap. -daemon runs
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vde_switch in the background. -hub tells VDE to broadcast the message to all
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segment, just like real hub that you use on real network.
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<ip> is the ip address of the gateway you want to use for the guest
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OS(es). For example:
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# ifconfig tap0 192.168.254.254
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will make 192.168.254.254 the gateway between guest and host, and your
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guest OS(es) will belong to the subnet 192.168.254.0 with a netmask of 255.255.255.0
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and an ip address of 192.168.254.XXX (where you get to pick the XXX). You must have
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the IP of the qemu guest and the IP of the gateway on the same subnet! While it
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may be possible to have them on separate subnets, it will certainly be harder
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to configure (and you won't like the way your routing tables will look either).
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[Sidebar: The "gateway" is actually the host OS itself on the tap0 interface.
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The host on the tap0 interface, aka 192.168.254.254, routes between the guest
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OS and the host's eth0 interface (which on is the real network). The host on the
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eth0 interface (ex. 192.168.0.2) can then route between the tap0 interface and
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the real network / the internet.]
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(Note that you might be required to do this:
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# ifconfig tap0 192.168.254.254 netmask 255.255.255.0
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Normally ifconfig should pick the correct netmask for you, but if it doesn't
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for some reason then you will have to specify it manually. See ifconfig(8) for
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details.
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)
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Note that you must run this before you run your firewall. I found it helpful
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to put this into a script, and have the script load before the firewall does.
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Firewall configuration
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You will need to enable masquerading between tap0 and your local area
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network (for example, eth0). You will also need to enable masquerading between
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tap0 and ppp0 if you use a dialup connection to the internet. The commands
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# echo "1" > /proc/sys/net/ipv4/ip_forward
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# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
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# iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
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will allow you to enable this manually.
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-----------------------------------------------------------------------------
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Slirp networking
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What is slirp networking?
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Slirp was an early program that existed before the masses knew of the internet.
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Back then, those who knew of it could access it only in one way: through a
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Unix shell account (or other such terminal account). This meant that one had to
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do all the things they wanted to in that terminal window. Back then, there were
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two dial up protocols: PPP and SLIP. PPP is now the standard but back then SLIP
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was more common (as it was cheaper).
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Slirp was designed to turn those shell accounts into SLIP connections. It worked
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by converting SLIP packets into socket connections. What you had to do was to
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run slirp on the computer you had the shell account on, and then connect your
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SLIP driver/dialer to the terminal slirp was running on (normally this
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'terminal' was in fact a modem). Slirp would then interpret the data that SLIP
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sent and transfer the data between the user's computer and the internet. To
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the user, it looked like they were actually connected directly to the internet
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through a firewall.
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Slirp is not used today (to the best of my knowledge) but the innovative idea it
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had is used by both qemu and vde. Instead of converting SLIP packets however,
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they convert ethernet packets. qemu's slirp networking is similar to vde's
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but it is simpler to use and also limited to a single qemu instance (you can
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not link multiple guest OSes together on the same network with slirp networking
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unless you use VDE).
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How to enable slirp networking?
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This is very similar to TUNTAP networking in the previous section, but the
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commands are slightly different. In addition, you do not need to set up
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routing or firewall rules.
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First off, you load vde_switch (no parameters are required for this case,
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although you can pass the -unix parameter if you want to use a different
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socket - required if you already have tuntap networking on the default
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socket).
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vde_switch
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or
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vde_switch -unix /tmp/unx.ctl
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The latter is required if you are running both slirp and tuntap or multiple
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slirp networks (for that matter, if you are running multiple tuntap networks).
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More on that later.
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Now you need the slirpvde command. slirpvde is the utilitry that provides the
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slirp functionality - it intercepts ethernet packets on the network and
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forwards them through the real network via emulation. To use it, you want
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to do this:
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slirpvde -s /tmp/unx.ctl -n 192.168.2.0 -d
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The -s tells slirpvde that vde_switch is running on /tmp/unx.ctl [this switch
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can be omitted if you called vde_switch by itself]. The -d switch tells
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slirpvde to emulate a DHCP server. This is not required but it allows for
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automatic configuration of the guest OS (it is basicly the same as qemu's
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builtin DHCP server). Depending on your needs, you may be better off running
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a real DHCP server in one of the guest OSes.
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The last option, -n, tells slirpvde
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what subnet the network should be on (this is also used by the DHCP server to
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figure out what ip addresses to assign). The gateway ip when using slirpvde
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is X.X.X.2 (where X.X.X equals the first 3 parts of the subnet you passed to
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it via -n, in this example 192.168.2) and the default DNS server is X.X.X.3
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You can not change the gateway ip to something other than .2 and the DNS ip
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to something other than .3 unless you change the source in slirpvde and
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recompile.
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-----------------------------------------------------------------------------
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Setting up qemu
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How to set up the guest OS
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Set up the guest OS so that the default route is through the gateway
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ip, <ip> (for example 192.168.254.254). Also set up the subnet and netmask
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parameters as appropriate (for example 192.168.254.0 and 255.255.255.0).
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The guest OS should see the ethernet device and be able to use it to access
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the gateway. (Caveat: I haven't been able to do this for MS-DOS, and for Minix
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2.0.4 I had to apply a patch to qemu since Minix is broken. Uodate: Minix 2.0.4
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is still broken but a patch has been released to fix it. Using this patch,
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Minix works on a vanilla qemu.) Also don't forget to set up the IP of the guest
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OS itself (for example 192.168.254.1).
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-----------------------------------------------------------------------------
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Credits
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This HOWTO relied heavily on the documentation that Renzo wrote for
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vde-1.4.1.
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Thanks to Mulyadi Santosa for helping with the first revision of
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this document, and to Renzo for his input. (P.S. Will add info for ale4net
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and slirpvde as soon as I figure out how to use it ;)
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