virtualbox, taps and bridges

[Karl Auer]

On Mon, 2008-10-06 at 10:08 +0000, Cameron Hutchison wrote:
> Without any details of how you've set up your "bridges and taps", its a
> little difficult to get any insight to what your problem may be. I
> cannot answer your original question regarding a link to another posting
> that may have your answer, but I have fiddled with virtualbox, bridges
> and taps before and would happy to help if I can.

It all started with me asking which of the many HowTos I should follow.
There was no real answer to that one :-)

Anyway, the situation I got to was that the guest could access the host,
the host could access the guest, the guest could access the Internet,
the Internet could access the guest - but the host couldn't access
anything outside it's own subnet!

The script below got me to that point (virtualbox was set to use tap1
and "Host Interface"). It was cobbled together over several hours from
hints and ideas from various sources. It is to be run as root (i.e.,
with sudo).

I think the line "ifconfig $IFACE 0.0.0.0" is suspect, but I gave up
before I got around the testing variations on that. One of the irritants
in all the HowTos was that they gave no indication at all about *why*
they took various steps. If one doesn't know the why of a thing, it's
very hard to adapt or correct it.

It would be nice to solve the problem and be able to use virtualbox, as
VMWare is a bit heavy duty, and I loath their slow, clumsy new Web
interface.

Any clues you could give me would be most appreciated. Thanks!

Regards, K.

#!/bin/sh

OPT=$1

if [ -z $OPT ] ; then
   echo "please specify one of \"start\" or \"stop\""
   exit 1 ;
fi

if [ -z $2 ] ; then
   echo "defaulting to use eth0"
   IFACE=eth0
else
   $IFACE=$2
fi

PATH=/sbin:/usr/bin:/bin:/usr/sbin

if [ $OPT = "start" ] ; then
   # create the bridge
   brctl addbr br0

   # add the real ethernet interface to the bridge
   ifconfig $IFACE 0.0.0.0
   brctl addif br0 $IFACE

   # give the bridge an IP address
   ip link set up dev br0
   dhclient br0

   # create a tap
   tunctl -t tap1 -u kauer > /dev/nul
   ip link set up dev tap1

   # add the tap interface to the bridge too
   brctl addif br0 tap1
fi

if [ $OPT = "stop" ] ; then
   brctl delif br0 $IFACE
   brctl delif br0 tap1
   ifconfig tap1 down
   tunctl -d tap1 > /dev/nul
   ifconfig br0 down
   brctl delbr br0
fi

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Karl Auer (kauer at biplane.com.au)                   +61-2-64957160 (h)
http://www.biplane.com.au/~kauer/                  +61-428-957160 (mob)

GPG fingerprint: DD23 0DF3 2260 3060 7FEC 5CA8 1AF6 D9E3 CFEE 6B28

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