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This fixes https://bugzilla.redhat.com/show_bug.cgi?id=609463 The problem was that, since a bridge always acquires the MAC address of the connected interface with the numerically lowest MAC, as guests are started and stopped, it was possible for the MAC address to change over time, and this change in the network was being detected by Windows 7 (it sees the MAC of the default route change), so on each reboot it would bring up a dialog box asking about this "new network". The solution is to create a dummy tap interface with a MAC guaranteed to be lower than any guest interface's MAC, and attach that tap to the bridge as soon as it's created. Since all guest MAC addresses start with 0xFE, we can just generate a MAC with the standard "0x52, 0x54, 0" prefix, and it's guaranteed to always win (physical interfaces are never connected to these bridges, so we don't need to worry about competing numerically with them). Note that the dummy tap is never set to IFF_UP state - that's not necessary in order for the bridge to take its MAC, and not setting it to UP eliminates the clutter of having an (eg) "virbr0-nic" displayed in the output of the ifconfig command. I chose to not auto-generate the MAC address in the network XML parser, as there are likely to be consumers of that API that don't need or want to have a MAC address associated with the bridge. Instead, in bridge_driver.c when the network is being defined, if there is no MAC, one is generated. To account for virtual network configs that already exist when upgrading from an older version of libvirt, I've added a %post script to the specfile that searches for all network definitions in both the config directory (/etc/libvirt/qemu/networks) and the state directory (/var/lib/libvirt/network) that are missing a mac address, generates a random address, and adds it to the config (and a matching address to the state file, if there is one). docs/formatnetwork.html.in: document <mac address.../> docs/schemas/network.rng: add nac address to schema libvirt.spec.in: %post script to update existing networks src/conf/network_conf.[ch]: parse and format <mac address.../> src/libvirt_private.syms: export a couple private symbols we need src/network/bridge_driver.c: auto-generate mac address when needed, create dummy interface if mac address is present. tests/networkxml2xmlin/isolated-network.xml tests/networkxml2xmlin/routed-network.xml tests/networkxml2xmlout/isolated-network.xml tests/networkxml2xmlout/routed-network.xml: add mac address to some tests
277 lines
13 KiB
HTML
277 lines
13 KiB
HTML
<html>
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<body>
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<h1>Network XML format</h1>
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<ul id="toc">
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</ul>
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<p>
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This page provides an introduction to the network XML format. For background
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information on the concepts referred to here, consult the <a href="archnetwork.html">network driver architecture</a>
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page.
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</p>
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<h2><a name="elements">Element and attribute overview</a></h2>
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<p>
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The root element required for all virtual networks is
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named <code>network</code> and has no attributes.
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The network XML format is available <span class="since">since 0.3.0</span>
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</p>
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<h3><a name="elementsMetadata">General metadata</a></h3>
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<p>
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The first elements provide basic metadata about the virtual
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network.
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</p>
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<pre>
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<network>
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<name>default</name>
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<uuid>3e3fce45-4f53-4fa7-bb32-11f34168b82b</uuid>
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...</pre>
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<dl>
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<dt><code>name</code></dt>
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<dd>The content of the <code>name</code> element provides
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a short name for the virtual network. This name should
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consist only of alpha-numeric characters and is required
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to be unique within the scope of a single host. It is
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used to form the filename for storing the persistent
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configuration file. <span class="since">Since 0.3.0</span></dd>
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<dt><code>uuid</code></dt>
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<dd>The content of the <code>uuid</code> element provides
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a globally unique identifier for the virtual network.
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The format must be RFC 4122 compliant, eg <code>3e3fce45-4f53-4fa7-bb32-11f34168b82b</code>.
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If omitted when defining/creating a new network, a random
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UUID is generated. <span class="since">Since 0.3.0</span></dd>
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</dl>
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<h3><a name="elementsConnect">Connectivity</a></h3>
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<p>
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The next set of elements control how a virtual network is
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provided connectivity to the physical LAN (if at all).
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</p>
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<pre>
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...
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<bridge name="virbr0" stp="on" delay="5"/>
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<domain name="example"/>
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<forward mode="nat" dev="eth0"/>
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...</pre>
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<dl>
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<dt><code>bridge</code></dt>
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<dd>The <code>name</code> attribute on the <code>bridge</code> element
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defines the name of a bridge device which will be used to construct
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the virtual network. The virtual machines will be connected to this
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bridge device allowing them to talk to each other. The bridge device
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may also be connected to the LAN. It is recommended that bridge
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device names started with the prefix <code>vir</code>, but the name
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<code>virbr0</code> is reserved for the "default" virtual network.
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This element should always be provided when defining a new network.
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Attribute <code>stp</code> specifies if Spanning Tree Protocol is
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'on' or 'off' (default is 'on'). Attribute <code>delay</code> sets
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the bridge's forward delay value in seconds (default is 0).
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<span class="since">Since 0.3.0</span>
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</dd>
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<dt><code>domain</code></dt>
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<dd>
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The <code>name</code> attribute on the <code>domain</code> element
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defines the DNS domain of the DHCP server. This element is optional.
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<span class="since">Since 0.4.5</span>
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</dd>
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<dt><code>forward</code></dt>
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<dd>Inclusion of the <code>forward</code> element indicates that
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the virtual network is to be connected to the physical
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LAN. the <code>mode</code> attribute determines the method of
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forwarding; possible selections are 'nat' and 'route'. If mode
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is not specified, NAT forwarding will be used for
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connectivity. If a network has any IPv6 addresses defined,
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even if <code>mode</code> is given as 'nat', the IPv6 traffic
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will be forwarded using routing, since IPv6 has no concept of NAT.
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Firewall rules will allow forwarding to any other network device whether
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ethernet, wireless, dialup, or VPN. If the <code>dev</code> attribute
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is set, the firewall rules will restrict forwarding to the named
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device only. If the <code>mode</code> attribute is set to <code>route</code>
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then the traffic will not have NAT applied. This presumes that the
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local LAN router has suitable routing table entries to return traffic
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to this host. <span class="since">Since 0.3.0; 'mode' attribute since
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0.4.2</span></dd>
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</dl>
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<h3><a name="elementsAddress">Addressing</a></h3>
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<p>
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The final set of elements define the addresses (IPv4 and/or
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IPv6, as well as MAC) to be assigned to the bridge device
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associated with the virtual network, and optionally enable DHCP
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services.
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</p>
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<pre>
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...
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<mac address='00:16:3E:5D:C7:9E'/>
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<ip address="192.168.122.1" netmask="255.255.255.0">
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<dhcp>
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<range start="192.168.122.100" end="192.168.122.254" />
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<host mac="00:16:3e:77:e2:ed" name="foo.example.com" ip="192.168.122.10" />
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<host mac="00:16:3e:3e:a9:1a" name="bar.example.com" ip="192.168.122.11" />
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</dhcp>
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</ip>
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</network></pre>
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<dl>
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<dt><code>mac</code></dt>
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<dd>The <code>address</code> attribute defines a MAC
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(hardware) address formatted as 6 groups of 2-digit
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hexadecimal numbers, the groups separated by colons
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(eg, <code>"52:54:00:1C:DA:2F"</code>). This MAC address is
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assigned to the bridge device when it is created. Generally
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it is best to not specify a MAC address when creating a
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network - in this case, if a defined MAC address is needed for
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proper operation, libvirt will automatically generate a random
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MAC address and save it in the config. Allowing libvirt to
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generate the MAC address will assure that it is compatible
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with the idiosyncrasies of the platform where libvirt is
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running. <span class="since">Since 0.8.8</span>
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</dd>
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<dt><code>ip</code></dt>
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<dd>The <code>address</code> attribute defines an IPv4 address in
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dotted-decimal format, or an IPv6 address in standard
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colon-separated hexadecimal format, that will be configured on
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the bridge
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device associated with the virtual network. To the guests this
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address will be their default route. For IPv4 addresses, the <code>netmask</code>
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attribute defines the significant bits of the network address,
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again specified in dotted-decimal format. For IPv6 addresses,
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and as an alternate method for IPv4 addresses, you can specify
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the significant bits of the network address with the <code>prefix</code>
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attribute, which is an integer (for example, <code>netmask='255.255.255.0'</code>
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could also be given as <code>prefix='24'</code>. The <code>family</code>
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attribute is used to specify the type of address - 'ipv4' or 'ipv6'; if no
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<code>family</code> is given, 'ipv4' is assumed. A network can have more than
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one of each family of address defined, but only a single address can have a
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<code>dhcp</code> or <code>tftp</code> element. <span class="since">Since 0.3.0;
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IPv6, multiple addresses on a single network, <code>family</code>, and
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<code>prefix</code> since 0.8.7</span>
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</dd><dt><code>tftp</code></dt><dd>Immediately within
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the <code>ip</code> element there is an optional <code>tftp</code>
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element. The presence of this element and of its attribute
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<code>root</code> enables TFTP services. The attribute specifies
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the path to the root directory served via TFTP. <code>tftp</code> is not
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supported for IPv6 addresses, can only be specified on a single IPv4 address
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per network.
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<span class="since">Since 0.7.1</span>
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</dd><dt><code>dhcp</code></dt><dd>Also within the <code>ip</code> element there is an
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optional <code>dhcp</code> element. The presence of this element
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enables DHCP services on the virtual network. It will further
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contain one or more <code>range</code> elements. The
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<code>dhcp</code> element is not supported for IPv6, and
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is only supported on a single IP address per network for IPv4.
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<span class="since">Since 0.3.0</span>
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</dd>
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<dt><code>range</code></dt>
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<dd>The <code>start</code> and <code>end</code> attributes on the
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<code>range</code> element specify the boundaries of a pool of
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IPv4 addresses to be provided to DHCP clients. These two addresses
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must lie within the scope of the network defined on the parent
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<code>ip</code> element. <span class="since">Since 0.3.0</span>
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</dd>
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<dt><code>host</code></dt>
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<dd>Within the <code>dhcp</code> element there may be zero or more
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<code>host</code> elements; these specify hosts which will be given
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names and predefined IP addresses by the built-in DHCP server. Any
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such element must specify the MAC address of the host to be assigned
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a given name (via the <code>mac</code> attribute), the IP to be
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assigned to that host (via the <code>ip</code> attribute), and the
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name to be given that host by the DHCP server (via the
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<code>name</code> attribute). <span class="since">Since 0.4.5</span>
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</dd><dt><code>bootp</code></dt><dd>The optional <code>bootp</code>
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element specifies BOOTP options to be provided by the DHCP server.
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Two attributes are supported: <code>file</code> is mandatory and
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gives the file to be used for the boot image; <code>server</code> is
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optional and gives the address of the TFTP server from which the boot
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image will be fetched. <code>server</code> defaults to the same host
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that runs the DHCP server, as is the case when the <code>tftp</code>
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element is used. The BOOTP options currently have to be the same
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for all address ranges and statically assigned addresses.<span
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class="since">Since 0.7.1 (<code>server</code> since 0.7.3).</span>
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</dd>
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</dl>
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<h2><a name="examples">Example configuration</a></h2>
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<h3><a name="examplesNAT">NAT based network</a></h3>
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<p>
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This example is the so called "default" virtual network. It is
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provided and enabled out-of-the-box for all libvirt installations.
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This is a configuration that allows guest OS to get outbound
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connectivity regardless of whether the host uses ethernet, wireless,
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dialup, or VPN networking without requiring any specific admin
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configuration. In the absence of host networking, it at least allows
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guests to talk directly to each other.
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</p>
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<pre>
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<network>
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<name>default</name>
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<bridge name="virbr0" />
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<forward mode="nat"/>
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<ip address="192.168.122.1" netmask="255.255.255.0">
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<dhcp>
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<range start="192.168.122.2" end="192.168.122.254" />
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</dhcp>
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</ip>
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</network></pre>
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<h3><a name="examplesRoute">Routed network config</a></h3>
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<p>
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This is a variant on the default network which routes traffic
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from the virtual network to the LAN without applying any NAT.
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It requires that the IP address range be pre-configured in the
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routing tables of the router on the host network. This example
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further specifies that guest traffic may only go out via the
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<code>eth1</code> host network device.
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</p>
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<pre>
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<network>
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<name>local</name>
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<bridge name="virbr1" />
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<forward mode="route" dev="eth1"/>
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<ip address="192.168.122.1" netmask="255.255.255.0">
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<dhcp>
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<range start="192.168.122.2" end="192.168.122.254" />
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</dhcp>
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</ip>
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</network></pre>
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<h3><a name="examplesPrivate">Isolated network config</a></h3>
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<p>
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This variant provides a completely isolated private network
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for guests. The guests can talk to each other, and the host
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OS, but cannot reach any other machines on the LAN, due to
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the omission of the <code>forward</code> element in the XML
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description.
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</p>
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<pre>
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<network>
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<name>private</name>
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<bridge name="virbr2" />
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<ip address="192.168.152.1" netmask="255.255.255.0">
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<dhcp>
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<range start="192.168.152.2" end="192.168.152.254" />
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</dhcp>
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</ip>
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</network></pre>
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</body>
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</html>
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