Le 01/12/2014 23:13, Bruce Dubbs a écrit :
Pierre Labastie wrote:
I can do that, but would like to discuss first.
As the book says, networking can be brought up by adding -net nic -net
user to the qemu line. The problem with that is that it doesn't set up
forwarding or configure the host.
For example, my local network is set up on 192.168.0.x and the qemu
dhcp server sets up the client as 10.0.2.15. I can't ping anything on
the 192 network from the client or vice versa.
If we do expand the discussion to add
-net user,hostfwd=tcp::2222-10.0.2.15:22
we still would have problems getting out. For instance ntp or dns
would not work on the guest AFAICT. We also couldn't ping the client
from the host or other network system. In other words, I think the
hostfwd solution is a limited solution.
I may be wrong here. If so, please tell me what else is needed.
When using "-net user":
I think (almost) everything on tcp and udp works _from_ the guest. There
is a virtual DNS at IP 10.0.2.3. I am not sure about NTP, and sure that
ping does not reach anything beyond the host at 10.0.2.2. There is also
a samba server, which I have never tried.
In the other direction, you have to set up a port forwarding for each
port, which may become complicated if you need several accesses to the
guest. Furthermore, only tcp and udp protocols can be forwarded (so not
ping for example).
When using "-net tap" + bridging:
As said in the book, you can make the VM appear as a machine on the
local network, allowing two-way accesses. The only reason for not using
it, is that qemu, ip and brctl need to be setgid and as noted wy the OP,
their capabilities have to be changed using setcap. Otherwise, running
qemu as root is possible too.
So surely, when full access is needed, bridging is the way to go (some
docs talk also about VDE, but I have never tried). But the user network
stack provides a quick and dirty way to access internet from the guest,
while port forwarding allows to provide limited access from the exterior
to the guest.
Some doc:
https://people.gnome.org/~markmc/qemu-networking.html (concise
introduction to all qemu networking possibilities).
https://wiki.archlinux.org/index.php/Qemu (more detailed).
Pierre
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