net.rst (4204B)
1 .. _pcsys_005fnetwork: 2 3 Network emulation 4 ----------------- 5 6 QEMU can simulate several network cards (e.g. PCI or ISA cards on the PC 7 target) and can connect them to a network backend on the host or an 8 emulated hub. The various host network backends can either be used to 9 connect the NIC of the guest to a real network (e.g. by using a TAP 10 devices or the non-privileged user mode network stack), or to other 11 guest instances running in another QEMU process (e.g. by using the 12 socket host network backend). 13 14 Using TAP network interfaces 15 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 16 17 This is the standard way to connect QEMU to a real network. QEMU adds a 18 virtual network device on your host (called ``tapN``), and you can then 19 configure it as if it was a real ethernet card. 20 21 Linux host 22 ^^^^^^^^^^ 23 24 As an example, you can download the ``linux-test-xxx.tar.gz`` archive 25 and copy the script ``qemu-ifup`` in ``/etc`` and configure properly 26 ``sudo`` so that the command ``ifconfig`` contained in ``qemu-ifup`` can 27 be executed as root. You must verify that your host kernel supports the 28 TAP network interfaces: the device ``/dev/net/tun`` must be present. 29 30 See :ref:`sec_005finvocation` to have examples of command 31 lines using the TAP network interfaces. 32 33 Windows host 34 ^^^^^^^^^^^^ 35 36 There is a virtual ethernet driver for Windows 2000/XP systems, called 37 TAP-Win32. But it is not included in standard QEMU for Windows, so you 38 will need to get it separately. It is part of OpenVPN package, so 39 download OpenVPN from : https://openvpn.net/. 40 41 Using the user mode network stack 42 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 43 44 By using the option ``-net user`` (default configuration if no ``-net`` 45 option is specified), QEMU uses a completely user mode network stack 46 (you don't need root privilege to use the virtual network). The virtual 47 network 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 56 The QEMU VM behaves as if it was behind a firewall which blocks all 57 incoming connections. You can use a DHCP client to automatically 58 configure the network in the QEMU VM. The DHCP server assign addresses 59 to the hosts starting from 10.0.2.15. 60 61 In order to check that the user mode network is working, you can ping 62 the address 10.0.2.2 and verify that you got an address in the range 63 10.0.2.x from the QEMU virtual DHCP server. 64 65 Note that ICMP traffic in general does not work with user mode 66 networking. ``ping``, aka. ICMP echo, to the local router (10.0.2.2) 67 shall work, however. If you're using QEMU on Linux >= 3.0, it can use 68 unprivileged ICMP ping sockets to allow ``ping`` to the Internet. The 69 host admin has to set the ping_group_range in order to grant access to 70 those sockets. To allow ping for GID 100 (usually users group):: 71 72 echo 100 100 > /proc/sys/net/ipv4/ping_group_range 73 74 When using the built-in TFTP server, the router is also the TFTP server. 75 76 When using the ``'-netdev user,hostfwd=...'`` option, TCP or UDP 77 connections can be redirected from the host to the guest. It allows for 78 example to redirect X11, telnet or SSH connections. 79 80 Hubs 81 ~~~~ 82 83 QEMU can simulate several hubs. A hub can be thought of as a virtual 84 connection between several network devices. These devices can be for 85 example QEMU virtual ethernet cards or virtual Host ethernet devices 86 (TAP devices). You can connect guest NICs or host network backends to 87 such a hub using the ``-netdev 88 hubport`` or ``-nic hubport`` options. The legacy ``-net`` option also 89 connects the given device to the emulated hub with ID 0 (i.e. the 90 default hub) unless you specify a netdev with ``-net nic,netdev=xxx`` 91 here. 92 93 Connecting emulated networks between QEMU instances 94 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 95 96 Using the ``-netdev socket`` (or ``-nic socket`` or ``-net socket``) 97 option, it is possible to create emulated networks that span several 98 QEMU instances. See the description of the ``-netdev socket`` option in 99 :ref:`sec_005finvocation` to have a basic 100 example.