Re: Shared Network -vs- Virtual Switch?

Thank you for your detailed response.  This helps.


On 6/30/05 11:44 AM, Tony Kavadias: 
I am sure others may provide a short-whinded
answer to your question, so I am going to provide
you with a longer one.


"Shared networking" is a way for multiple virtual
machines to share a Macintosh networking interface.
The Macintosh itself continues to use an obtained or
configured IP address while the virtual machines
get their own private IP address from the Macintosh
itself via an internal DHCP service and a NAT gateway
running on behalf of Virtual PC.  (Ahh, the magic of
kernel extensions... !)

This is handy for when you are on a network where
your Mac can only have one IP address (because your
network administrator has provided you with only one)
for a given interface, but you want your virtual
machines to gain access to network resources via that
interface.  For shared networking to work, the operating
systems in your virtual machines must be configured to
use DHCP in order to obtain their IP addresses from
Virtual PC.  The IP addresses provided by Virtual PC
are in the 192.168.131.0 network.

"Virtual switch" is effectively a way for each virtual
machine to obtain "direct" access to one of your Mac's
network interfaces.  The Macintosh and your virtual
machines can share the use of a physical interface,
but only as appearing as isolated interfaces (one with
the real, and others with a fabricated MAC address) on
the network.

On my Mac, the one Ethernet interface (en0) has two
concurrent MAC addresses:

[isenmouthe:~] tonza{2}% arp -a
? (10.0.1.2) at 0:3:ff:9b:ee:38 on en0 [ethernet]
... other entries...
[isenmouthe:~] tonza{3}% _

You're going to have to trust me as to the authenticity of
this program's output, here!  I truncated the output to
make the all-important entry stand out.

Here, the address 10.0.1.2 is actually resident in my
Macintosh, and relates to the interface used by my virtual
machine in Virtual PC -- it is not another device somewhere
on my network.  This virtual device has its own MAC address,
which is not the same as the Mac's own MAC address for en0:

[isenmouthe:~] tonza{11}% ifconfig en0 en1
en0: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
inet 10.0.1.204 netmask 0xffffff00 broadcast 10.0.1.255
ether 00:0a:95:9d:ee:38
media: autoselect (100baseTX <full-duplex>) status: active
supported media: ... abridged...

The address 10.0.1.2 was obtained from an external DHCP
server that exists somewhere in my 10.0.1.0 network.  NAT
services don't exist under virtual switch networking, so
if I was to jump on another machine and send broadcast
packets on the 10.0.1.0 network, my virtual machine will
see them and probably react to them like the Mac could on
its IP address of 10.0.1.204.

Incidentally, as long as you do not cause any IP conflicts
on your netowrk, your virtual machines' IP addresses can
be manually configured under virtual switch networking.
Thus, if you need to have your virtual machines configured
using fixed (static) IP addresses provided by the operating
system running within them, virtual switch networking must
be used.

In general, virtual switch is more efficient to Mac OS X
than shared networking is (shared networking needs to run a
DHCP service and continuously manage NAT tables), but
there are circumstances where you will have to resort to
one or the other networking type due to constraints imposed
by your network administrator or by your networking
requirements.

--
--  tonza.



"Mark" <xpmark@xxxxxxxxxxx> wrote in message news:OdozMbXfFHA.1148@xxxxxxxxxxxxxxxxxxxxxxx

What are the differences between 'Shared Network' and 'Virtual Switch' in Virtual PC for Mac OS X 6.1.1? 



.

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