1.. _Network_Emulation: 2 3Network emulation 4----------------- 5 6QEMU can simulate several network cards (e.g. PCI or ISA cards on the PC 7target) and can connect them to a network backend on the host or an 8emulated hub. The various host network backends can either be used to 9connect the NIC of the guest to a real network (e.g. by using a TAP 10devices or the non-privileged user mode network stack), or to other 11guest instances running in another QEMU process (e.g. by using the 12socket host network backend). 13 14Using TAP network interfaces 15~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 16 17This is the standard way to connect QEMU to a real network. QEMU adds a 18virtual network device on your host (called ``tapN``), and you can then 19configure it as if it was a real ethernet card. 20 21Linux host 22^^^^^^^^^^ 23 24As an example, you can download the ``linux-test-xxx.tar.gz`` archive 25and copy the script ``qemu-ifup`` in ``/etc`` and configure properly 26``sudo`` so that the command ``ifconfig`` contained in ``qemu-ifup`` can 27be executed as root. You must verify that your host kernel supports the 28TAP network interfaces: the device ``/dev/net/tun`` must be present. 29 30See :ref:`sec_005finvocation` to have examples of command 31lines using the TAP network interfaces. 32 33Windows host 34^^^^^^^^^^^^ 35 36There is a virtual ethernet driver for Windows 2000/XP systems, called 37TAP-Win32. But it is not included in standard QEMU for Windows, so you 38will need to get it separately. It is part of OpenVPN package, so 39download OpenVPN from : https://openvpn.net/. 40 41Using the user mode network stack 42~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 43 44By using the option ``-net user`` (default configuration if no ``-net`` 45option is specified), QEMU uses a completely user mode network stack 46(you don't need root privilege to use the virtual network). The virtual 47network configuration is the following:: 48 49 guest (10.0.2.15) <------> Firewall/DHCP server <-----> Internet 50 | (10.0.2.2) 51 | 52 ----> DNS server (10.0.2.3) 53 | 54 ----> SMB server (10.0.2.4) 55 56The QEMU VM behaves as if it was behind a firewall which blocks all 57incoming connections. You can use a DHCP client to automatically 58configure the network in the QEMU VM. The DHCP server assign addresses 59to the hosts starting from 10.0.2.15. 60 61In order to check that the user mode network is working, you can ping 62the address 10.0.2.2 and verify that you got an address in the range 6310.0.2.x from the QEMU virtual DHCP server. 64 65Note that ICMP traffic in general does not work with user mode 66networking. ``ping``, aka. ICMP echo, to the local router (10.0.2.2) 67shall work, however. If you're using QEMU on Linux >= 3.0, it can use 68unprivileged ICMP ping sockets to allow ``ping`` to the Internet. The 69host admin has to set the ping_group_range in order to grant access to 70those sockets. To allow ping for GID 100 (usually users group):: 71 72 echo 100 100 > /proc/sys/net/ipv4/ping_group_range 73 74When using the built-in TFTP server, the router is also the TFTP server. 75 76When using the ``'-netdev user,hostfwd=...'`` option, TCP or UDP 77connections can be redirected from the host to the guest. It allows for 78example to redirect X11, telnet or SSH connections. 79 80Hubs 81~~~~ 82 83QEMU can simulate several hubs. A hub can be thought of as a virtual 84connection between several network devices. These devices can be for 85example QEMU virtual ethernet cards or virtual Host ethernet devices 86(TAP devices). You can connect guest NICs or host network backends to 87such a hub using the ``-netdev 88hubport`` or ``-nic hubport`` options. The legacy ``-net`` option also 89connects the given device to the emulated hub with ID 0 (i.e. the 90default hub) unless you specify a netdev with ``-net nic,netdev=xxx`` 91here. 92 93Connecting emulated networks between QEMU instances 94~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 95 96Using the ``-netdev socket`` (or ``-nic socket`` or ``-net socket``) 97option, it is possible to create emulated networks that span several 98QEMU instances. See the description of the ``-netdev socket`` option in 99:ref:`sec_005finvocation` to have a basic 100example. 101