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diff --git a/docs/system/net.texi b/docs/system/net.texi new file mode 100644 index 0000000000..4a6fb2e6a8 --- /dev/null +++ b/docs/system/net.texi @@ -0,0 +1,96 @@ +@node pcsys_network +@section 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). + +@subsection 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 @code{tapN}), and you +can then configure it as if it was a real ethernet card. + +@subsubsection Linux host + +As an example, you can download the @file{linux-test-xxx.tar.gz} +archive and copy the script @file{qemu-ifup} in @file{/etc} and +configure properly @code{sudo} so that the command @code{ifconfig} +contained in @file{qemu-ifup} can be executed as root. You must verify +that your host kernel supports the TAP network interfaces: the +device @file{/dev/net/tun} must be present. + +See @ref{sec_invocation} to have examples of command lines using the +TAP network interfaces. + +@subsubsection 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 : @url{https://openvpn.net/}. + +@subsection Using the user mode network stack + +By using the option @option{-net user} (default configuration if no +@option{-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: + +@example + + 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) +@end example + +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. +@code{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 @code{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): + +@example +echo 100 100 > /proc/sys/net/ipv4/ping_group_range +@end example + +When using the built-in TFTP server, the router is also the TFTP +server. + +When using the @option{'-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. + +@subsection 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 @option{-netdev +hubport} or @option{-nic hubport} options. The legacy @option{-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 @option{-net nic,netdev=xxx} here. + +@subsection Connecting emulated networks between QEMU instances + +Using the @option{-netdev socket} (or @option{-nic socket} or +@option{-net socket}) option, it is possible to create emulated +networks that span several QEMU instances. +See the description of the @option{-netdev socket} option in the +@ref{sec_invocation,,Invocation chapter} to have a basic example. |