97 lines
4.2 KiB
Plaintext
97 lines
4.2 KiB
Plaintext
@node pcsys_network
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@section Network emulation
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QEMU can simulate several network cards (e.g. PCI or ISA cards on the PC
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target) and can connect them to a network backend on the host or an emulated
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hub. The various host network backends can either be used to connect the NIC of
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the guest to a real network (e.g. by using a TAP devices or the non-privileged
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user mode network stack), or to other guest instances running in another QEMU
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process (e.g. by using the socket host network backend).
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@subsection Using TAP network interfaces
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This is the standard way to connect QEMU to a real network. QEMU adds
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a virtual network device on your host (called @code{tapN}), and you
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can then configure it as if it was a real ethernet card.
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@subsubsection Linux host
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As an example, you can download the @file{linux-test-xxx.tar.gz}
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archive and copy the script @file{qemu-ifup} in @file{/etc} and
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configure properly @code{sudo} so that the command @code{ifconfig}
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contained in @file{qemu-ifup} can be executed as root. You must verify
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that your host kernel supports the TAP network interfaces: the
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device @file{/dev/net/tun} must be present.
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See @ref{sec_invocation} to have examples of command lines using the
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TAP network interfaces.
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@subsubsection Windows host
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There is a virtual ethernet driver for Windows 2000/XP systems, called
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TAP-Win32. But it is not included in standard QEMU for Windows,
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so you will need to get it separately. It is part of OpenVPN package,
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so download OpenVPN from : @url{https://openvpn.net/}.
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@subsection Using the user mode network stack
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By using the option @option{-net user} (default configuration if no
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@option{-net} option is specified), QEMU uses a completely user mode
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network stack (you don't need root privilege to use the virtual
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network). The virtual network configuration is the following:
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@example
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guest (10.0.2.15) <------> Firewall/DHCP server <-----> Internet
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----> DNS server (10.0.2.3)
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----> SMB server (10.0.2.4)
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@end example
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The QEMU VM behaves as if it was behind a firewall which blocks all
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incoming connections. You can use a DHCP client to automatically
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configure the network in the QEMU VM. The DHCP server assign addresses
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to the hosts starting from 10.0.2.15.
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In order to check that the user mode network is working, you can ping
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the address 10.0.2.2 and verify that you got an address in the range
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10.0.2.x from the QEMU virtual DHCP server.
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Note that ICMP traffic in general does not work with user mode networking.
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@code{ping}, aka. ICMP echo, to the local router (10.0.2.2) shall work,
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however. If you're using QEMU on Linux >= 3.0, it can use unprivileged ICMP
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ping sockets to allow @code{ping} to the Internet. The host admin has to set
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the ping_group_range in order to grant access to those sockets. To allow ping
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for GID 100 (usually users group):
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@example
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echo 100 100 > /proc/sys/net/ipv4/ping_group_range
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@end example
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When using the built-in TFTP server, the router is also the TFTP
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server.
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When using the @option{'-netdev user,hostfwd=...'} option, TCP or UDP
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connections can be redirected from the host to the guest. It allows for
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example to redirect X11, telnet or SSH connections.
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@subsection Hubs
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QEMU can simulate several hubs. A hub can be thought of as a virtual connection
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between several network devices. These devices can be for example QEMU virtual
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ethernet cards or virtual Host ethernet devices (TAP devices). You can connect
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guest NICs or host network backends to such a hub using the @option{-netdev
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hubport} or @option{-nic hubport} options. The legacy @option{-net} option
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also connects the given device to the emulated hub with ID 0 (i.e. the default
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hub) unless you specify a netdev with @option{-net nic,netdev=xxx} here.
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@subsection Connecting emulated networks between QEMU instances
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Using the @option{-netdev socket} (or @option{-nic socket} or
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@option{-net socket}) option, it is possible to create emulated
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networks that span several QEMU instances.
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See the description of the @option{-netdev socket} option in the
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@ref{sec_invocation,,Invocation chapter} to have a basic example.
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