mirror of
https://github.com/qemu/qemu.git
synced 2025-10-27 22:03:47 +00:00
189c099f75
While we are at it add a brief preamble that explains some of the common concepts in QEMU's device emulation which will hopefully lead to less confusing about our dizzying command line options. Signed-off-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Markus Armbruster <armbru@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Daniel P. Berrangé <berrange@redhat.com> Cc: Eduardo Habkost <ehabkost@redhat.com> Message-Id: <20210720232703.10650-3-alex.bennee@linaro.org>
101 lines
4.1 KiB
ReStructuredText
101 lines
4.1 KiB
ReStructuredText
.. _pcsys_005fnetwork:
|
|
|
|
Network emulation
|
|
-----------------
|
|
|
|
QEMU can simulate several network cards (e.g. PCI or ISA cards on the PC
|
|
target) and can connect them to a network backend on the host or an
|
|
emulated hub. The various host network backends can either be used to
|
|
connect the NIC of the guest to a real network (e.g. by using a TAP
|
|
devices or the non-privileged user mode network stack), or to other
|
|
guest instances running in another QEMU process (e.g. by using the
|
|
socket host network backend).
|
|
|
|
Using TAP network interfaces
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
This is the standard way to connect QEMU to a real network. QEMU adds a
|
|
virtual network device on your host (called ``tapN``), and you can then
|
|
configure it as if it was a real ethernet card.
|
|
|
|
Linux host
|
|
^^^^^^^^^^
|
|
|
|
As an example, you can download the ``linux-test-xxx.tar.gz`` archive
|
|
and copy the script ``qemu-ifup`` in ``/etc`` and configure properly
|
|
``sudo`` so that the command ``ifconfig`` contained in ``qemu-ifup`` can
|
|
be executed as root. You must verify that your host kernel supports the
|
|
TAP network interfaces: the device ``/dev/net/tun`` must be present.
|
|
|
|
See :ref:`sec_005finvocation` to have examples of command
|
|
lines using the TAP network interfaces.
|
|
|
|
Windows host
|
|
^^^^^^^^^^^^
|
|
|
|
There is a virtual ethernet driver for Windows 2000/XP systems, called
|
|
TAP-Win32. But it is not included in standard QEMU for Windows, so you
|
|
will need to get it separately. It is part of OpenVPN package, so
|
|
download OpenVPN from : https://openvpn.net/.
|
|
|
|
Using the user mode network stack
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
By using the option ``-net user`` (default configuration if no ``-net``
|
|
option is specified), QEMU uses a completely user mode network stack
|
|
(you don't need root privilege to use the virtual network). The virtual
|
|
network configuration is the following::
|
|
|
|
guest (10.0.2.15) <------> Firewall/DHCP server <-----> Internet
|
|
| (10.0.2.2)
|
|
|
|
|
----> DNS server (10.0.2.3)
|
|
|
|
|
----> SMB server (10.0.2.4)
|
|
|
|
The QEMU VM behaves as if it was behind a firewall which blocks all
|
|
incoming connections. You can use a DHCP client to automatically
|
|
configure the network in the QEMU VM. The DHCP server assign addresses
|
|
to the hosts starting from 10.0.2.15.
|
|
|
|
In order to check that the user mode network is working, you can ping
|
|
the address 10.0.2.2 and verify that you got an address in the range
|
|
10.0.2.x from the QEMU virtual DHCP server.
|
|
|
|
Note that ICMP traffic in general does not work with user mode
|
|
networking. ``ping``, aka. ICMP echo, to the local router (10.0.2.2)
|
|
shall work, however. If you're using QEMU on Linux >= 3.0, it can use
|
|
unprivileged ICMP ping sockets to allow ``ping`` to the Internet. The
|
|
host admin has to set the ping_group_range in order to grant access to
|
|
those sockets. To allow ping for GID 100 (usually users group)::
|
|
|
|
echo 100 100 > /proc/sys/net/ipv4/ping_group_range
|
|
|
|
When using the built-in TFTP server, the router is also the TFTP server.
|
|
|
|
When using the ``'-netdev user,hostfwd=...'`` option, TCP or UDP
|
|
connections can be redirected from the host to the guest. It allows for
|
|
example to redirect X11, telnet or SSH connections.
|
|
|
|
Hubs
|
|
~~~~
|
|
|
|
QEMU can simulate several hubs. A hub can be thought of as a virtual
|
|
connection between several network devices. These devices can be for
|
|
example QEMU virtual ethernet cards or virtual Host ethernet devices
|
|
(TAP devices). You can connect guest NICs or host network backends to
|
|
such a hub using the ``-netdev
|
|
hubport`` or ``-nic hubport`` options. The legacy ``-net`` option also
|
|
connects the given device to the emulated hub with ID 0 (i.e. the
|
|
default hub) unless you specify a netdev with ``-net nic,netdev=xxx``
|
|
here.
|
|
|
|
Connecting emulated networks between QEMU instances
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Using the ``-netdev socket`` (or ``-nic socket`` or ``-net socket``)
|
|
option, it is possible to create emulated networks that span several
|
|
QEMU instances. See the description of the ``-netdev socket`` option in
|
|
:ref:`sec_005finvocation` to have a basic
|
|
example.
|