docs/formatnwfilter.html.in

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   5     <h1>Network Filters</h1>
   6
   7     <ul id="toc">
   8     </ul>
   9
  10     <p>
  11       This page provides an introduction to libvirt's network filters,
  12       their goals, concepts and XML format.
  13     </p>
  14
  15     <h2><a id="goals">Goals and background</a></h2>
  16
  17     <p>
  18       The goal of the network filtering XML is to enable administrators
  19       of a virtualized system to configure and enforce network traffic
  20       filtering rules on virtual
  21       machines and manage the parameters of network traffic that
  22       virtual machines
  23       are allowed to send or receive.
  24       The network traffic filtering rules are
  25       applied on the host when a virtual machine is started. Since the
  26       filtering rules
  27       cannot be circumvented from within
  28       the virtual machine, it makes them mandatory from the point of
  29       view of a virtual machine user.
  30       <br/><br/>
  31       The network filter subsystem allows each virtual machine's network
  32       traffic filtering rules to be configured individually on a per
  33       interface basis. The rules are
  34       applied on the host when the virtual machine is started and can be modified
  35       while the virtual machine is running. The latter can be achieved by
  36       modifying the XML description of a network filter.
  37       <br/><br/>
  38       Multiple virtual machines can make use of the same generic network filter.
  39       When such a filter is modified, the network traffic filtering rules
  40       of all running virtual machines that reference this filter are updated.
  41       <br/><br/>
  42       Network filtering support is available <span class="since">since 0.8.1
  43       (QEMU, KVM)</span>
  44     </p>
  45
  46     <h2><a id="nwfconcepts">Concepts</a></h2>
  47     <p>
  48       The network traffic filtering subsystem enables configuration
  49       of network traffic filtering rules on individual network
  50       interfaces that are configured for certain types of
  51       network configurations. Supported network types are
  52     </p>
  53       <ul>
  54        <li><code>network</code></li>
  55        <li><code>ethernet</code> -- must be used in bridging mode</li>
  56        <li><code>bridge</code></li>
  57       </ul>
  58     <p>
  59     The interface XML is used to reference a top-level filter. In the
  60     following example, the interface description references
  61     the filter <code>clean-traffic</code>.
  62     </p>
  63 <pre>
  64 ...
  65 &lt;devices&gt;
  66   &lt;interface type='bridge'&gt;
  67     &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
  68     &lt;filterref filter='clean-traffic'/&gt;
  69   &lt;/interface&gt;
  70 &lt;/devices&gt;
  71 ...</pre>
  72
  73     <p>
  74     Network filters are written in XML and may either contain references
  75     to other filters, contain rules for traffic filtering, or
  76     hold a combination of both. The above referenced filter
  77     <code>clean-traffic </code> is a filter that only contains references to
  78     other filters and no actual filtering rules. Since references to
  79     other filters can be used, a <i>tree</i> of filters can be built.
  80     The <code>clean-traffic</code> filter can be viewed using the
  81     command <code>virsh nwfilter-dumpxml clean-traffic</code>.
  82     <br/><br/>
  83     As previously mentioned, a single network filter can be referenced
  84     by multiple virtual machines. Since interfaces will typically
  85     have individual parameters associated with their respective traffic
  86     filtering rules, the rules described in a filter XML can
  87     be parameterized with variables. In this case, the variable name
  88     is used in the filter XML and the name and value are provided at the
  89     place where the filter is referenced. In the
  90     following example, the interface description has been extended with
  91     the parameter <code>IP</code> and a dotted IP address as value.
  92     </p>
  93 <pre>
  94 ...
  95 &lt;devices&gt;
  96   &lt;interface type='bridge'&gt;
  97     &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
  98     &lt;filterref filter='clean-traffic'&gt;
  99       &lt;parameter name='IP' value='10.0.0.1'/&gt;
 100     &lt;/filterref&gt;
 101   &lt;/interface&gt;
 102 &lt;/devices&gt;
 103 ...</pre>
 104
 105     <p>
 106       In this particular example, the <code>clean-traffic</code> network
 107       traffic filter will be instantiated with the IP address parameter
 108       10.0.0.1 and enforce that the traffic from this interface will
 109       always be using 10.0.0.1 as the source IP address, which is
 110       one of the purposes of this particular filter.
 111       <br/><br/>
 112     </p>
 113
 114     <h3><a id="nwfconceptschains">Filtering chains</a></h3>
 115     <p>
 116       Filtering rules are organized in filter chains. These chains can be
 117       thought of as having a tree structure with packet
 118       filtering rules as entries in individual chains (branches). <br/>
 119       Packets start their filter evaluation in the <code>root</code> chain
 120       and can then continue their evaluation in other chains, return from
 121       those chains back into the <code>root</code> chain or be
 122       dropped or accepted by a filtering rule in one of the traversed chains.
 123       <br/>
 124       Libvirt's network filtering system automatically creates individual
 125       <code>root</code> chains for every virtual machine's network interface
 126       on which the user chooses to activate traffic filtering.
 127       The user may write filtering rules that are either directly instantiated
 128       in the <code>root</code> chain or may create protocol-specific
 129       filtering chains for efficient evaluation of protocol-specific rules.
 130       The following chains exist:
 131     </p>
 132     <ul>
 133      <li>root</li>
 134      <li>mac <span class="since">(since 0.9.8)</span></li>
 135      <li>stp (spanning tree protocol)
 136          <span class="since">(since 0.9.8)</span></li>
 137      <li>vlan (802.1Q) <span class="since">(since 0.9.8)</span></li>
 138      <li>arp, rarp</li>
 139      <li>ipv4</li>
 140      <li>ipv6</li>
 141     </ul>
 142     <p>
 143       <span class="since">Since 0.9.8</span> multiple chains evaluating the
 144       <code>mac</code>, <code>stp</code>, <code>vlan</code>,
 145       <code>arp</code>, <code>rarp</code>, <code>ipv4</code>, or
 146       <code>ipv6</code> protocol can be created using
 147       the protocol name only as a prefix in the chain's name. This for
 148       examples allows chains with names <code>arp-xyz</code> or
 149       <code>arp-test</code> to be specified and have ARP protocol packets
 150       evaluated in those chains.
 151     <br/><br/>
 152       The following filter shows an example of filtering ARP traffic
 153       in the <code>arp</code> chain.
 154     </p>
 155 <pre>
 156 &lt;filter name='no-arp-spoofing' chain='arp' priority='-500'&gt;
 157   &lt;uuid&gt;f88f1932-debf-4aa1-9fbe-f10d3aa4bc95&lt;/uuid&gt;
 158   &lt;rule action='drop' direction='out' priority='300'&gt;
 159     &lt;mac match='no' srcmacaddr='$MAC'/&gt;
 160   &lt;/rule&gt;
 161   &lt;rule action='drop' direction='out' priority='350'&gt;
 162     &lt;arp match='no' arpsrcmacaddr='$MAC'/&gt;
 163   &lt;/rule&gt;
 164   &lt;rule action='drop' direction='out' priority='400'&gt;
 165     &lt;arp match='no' arpsrcipaddr='$IP'/&gt;
 166   &lt;/rule&gt;
 167   &lt;rule action='drop' direction='in' priority='450'&gt;
 168     &lt;arp opcode='Reply'/&gt;
 169     &lt;arp match='no' arpdstmacaddr='$MAC'/&gt;
 170   &lt;/rule&gt;
 171   &lt;rule action='drop' direction='in' priority='500'&gt;
 172     &lt;arp match='no' arpdstipaddr='$IP'/&gt;
 173   &lt;/rule&gt;
 174   &lt;rule action='accept' direction='inout' priority='600'&gt;
 175     &lt;arp opcode='Request'/&gt;
 176   &lt;/rule&gt;
 177   &lt;rule action='accept' direction='inout' priority='650'&gt;
 178     &lt;arp opcode='Reply'/&gt;
 179   &lt;/rule&gt;
 180   &lt;rule action='drop' direction='inout' priority='1000'/&gt;
 181 &lt;/filter&gt;
 182 </pre>
 183     <p>
 184       The consequence of putting ARP-specific rules in the <code>arp</code>
 185       chain, rather than for example in the <code>root</code> chain, is that
 186       packets for any other protocol than ARP do not need to be evaluated by
 187       ARP protocol-specific rules. This improves the efficiency
 188       of the traffic filtering. However, one must then pay attention to only
 189       put filtering rules for the given protocol into the chain since
 190       any other rules will not be evaluated, i.e., an IPv4 rule will not
 191       be evaluated in the ARP chain since no IPv4 protocol packets will
 192       traverse the ARP chain.
 193       <br/><br/>
 194     </p>
 195     <h3><a id="nwfconceptschainpriorities">Filtering chain priorities</a></h3>
 196     <p>
 197       All chains are connected to the <code>root</code> chain. The order in
 198       which those chains are accessed is influenced by the priority of the
 199       chain. The following table shows the chains that can be assigned a
 200       priority and their default priorities.
 201     </p>
 202       <table class="top_table">
 203        <tr>
 204          <th> Chain (prefix) </th>
 205          <th> Default priority </th>
 206        </tr>
 207        <tr>
 208          <td>stp</td><td>-810</td>
 209        </tr>
 210        <tr>
 211          <td>mac</td><td>-800</td>
 212        </tr>
 213        <tr>
 214          <td>vlan</td><td>-750</td>
 215        </tr>
 216        <tr>
 217          <td>ipv4</td><td>-700</td>
 218        </tr>
 219        <tr>
 220          <td>ipv6</td><td>-600</td>
 221        </tr>
 222        <tr>
 223          <td>arp</td><td>-500</td>
 224        </tr>
 225        <tr>
 226          <td>rarp</td><td>-400</td>
 227        </tr>
 228       </table>
 229     <p>
 230       A chain with a lower priority value is accessed before one with a
 231       higher value.
 232       <br/>
 233       <span class="since">Since 0.9.8</span> the above listed chains
 234       can be assigned custom priorities by writing a value in the
 235       range [-1000, 1000] into the priority (XML) attribute in the filter
 236       node. The above example filter shows the default priority of -500
 237       for <code>arp</code> chains.
 238     </p>
 239     <h3><a id="nwfconceptsvars">Usage of variables in filters</a></h3>
 240     <p>
 241
 242       Two variables names have so far been reserved for usage by the
 243       network traffic filtering subsystem: <code>MAC</code> and
 244       <code>IP</code>.
 245       <br/><br/>
 246       <code>MAC</code> is the MAC address of the
 247       network interface. A filtering rule that references this variable
 248       will automatically be instantiated with the MAC address of the
 249       interface. This works without the user having to explicitly provide
 250       the MAC parameter. Even though it is possible to specify the MAC
 251       parameter similar to the IP parameter above, it is discouraged
 252       since libvirt knows what MAC address an interface will be using.
 253       <br/><br/>
 254       The parameter <code>IP</code> represents the IP address
 255       that the operating system inside the virtual machine is expected
 256       to use on the given interface. The <code>IP</code> parameter
 257       is special in so far as the libvirt daemon will try to determine
 258       the IP address (and thus the IP parameter's value) that is being
 259       used on an interface if the parameter
 260       is not explicitly provided but referenced.
 261       For current limitations on IP address detection, consult the
 262       <a href="#nwflimits">section on limitations</a> on how to use this
 263       feature and what to expect when using it.
 264       <br/><br/>
 265       The above-shown network filer <code>no-arp-spoofing</code>
 266       is an example of
 267       a network filter XML referencing the <code>MAC</code> and
 268       <code>IP</code> variables.
 269       <br/><br/>
 270       Note that referenced variables are always prefixed with the
 271       $ (dollar) sign. The format of the value of a variable
 272       must be of the type expected by the filter attribute in the
 273       XML. In the above example, the <code>IP</code> parameter
 274       must hold a dotted IP address in decimal numbers format.
 275       Failure to  provide the correct
 276       value type will result in the filter not being instantiatable
 277       and will prevent a virtual machine from starting or the
 278       interface from attaching when hotplugging is used. The types
 279       that are expected for each XML attribute are shown
 280       below.
 281       <br/><br/>
 282       <span class="since">Since 0.9.8</span> variables can contain lists of
 283       elements, e.g., the variable <code>IP</code> can contain multiple IP
 284       addresses that are valid on a particular interface. The notation for
 285       providing multiple elements for the IP variable is:
 286     </p>
 287 <pre>
 288 ...
 289 &lt;devices&gt;
 290   &lt;interface type='bridge'&gt;
 291     &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
 292     &lt;filterref filter='clean-traffic'&gt;
 293       &lt;parameter name='IP' value='10.0.0.1'/&gt;
 294       &lt;parameter name='IP' value='10.0.0.2'/&gt;
 295       &lt;parameter name='IP' value='10.0.0.3'/&gt;
 296     &lt;/filterref&gt;
 297   &lt;/interface&gt;
 298 &lt;/devices&gt;
 299 ...</pre>
 300     <p>
 301       This then allows filters to enable multiple IP addresses
 302       per interface. Therefore, with the list
 303       of IP address shown above, the following rule will create 3
 304       individual filtering rules, one for each IP address.
 305     </p>
 306 <pre>
 307 ...
 308 &lt;rule action='accept' direction='in' priority='500'&gt;
 309   &lt;tcp srpipaddr='$IP'/&gt;
 310 &lt;/rule&gt;
 311 ...
 312 </pre>
 313     <p>
 314       <span class="since">Since 0.9.10</span> it is possible to access
 315       individual elements of a variable holding a list of elements.
 316       A filtering rule like the following accesses the 2nd element
 317       of the variable DSTPORTS.
 318     </p>
 319 <pre>
 320 ...
 321 &lt;rule action='accept' direction='in' priority='500'&gt;
 322   &lt;udp dstportstart='$DSTPORTS[1]'/&gt;
 323 &lt;/rule&gt;
 324 ...
 325 </pre>
 326     <p>
 327       <span class="since">Since 0.9.10</span> it is possible to create
 328       filtering rules that instantiate all combinations of rules from
 329       different lists using the notation of
 330       <code>$VARIABLE[@&lt;iterator ID&gt;]</code>.
 331       The following rule allows a virtual machine to
 332       receive traffic on a set of ports, which are specified in DSTPORTS,
 333       from the set of source IP address specified in SRCIPADDRESSES.
 334       The rule generates all combinations of elements of the variable
 335       DSTPORT with those of SRCIPADDRESSES by using two independent
 336       iterators to access their elements.
 337     </p>
 338 <pre>
 339 ...
 340 &lt;rule action='accept' direction='in' priority='500'&gt;
 341   &lt;ip srcipaddr='$SRCIPADDRESSES[@1]' dstportstart='$DSTPORTS[@2]'/&gt;
 342 &lt;/rule&gt;
 343 ...
 344 </pre>
 345
 346     <p>
 347       In an example we assign concrete values to SRCIPADDRESSES and DSTPORTS
 348     </p>
 349 <pre>
 350 SRCIPADDRESSES = [ 10.0.0.1, 11.1.2.3 ]
 351 DSTPORTS = [ 80, 8080 ]
 352 </pre>
 353     <p>
 354       Accessing the variables using $SRCIPADDRESSES[@1] and $DSTPORTS[@2] would
 355       then result in all combinations of addresses and ports being created:
 356     </p>
 357 <pre>
 358 10.0.0.1, 80
 359 10.0.0.1, 8080
 360 11.1.2.3, 80
 361 11.1.2.3, 8080
 362 </pre>
 363     <p>
 364       Accessing the same variables using a single iterator, for example by using
 365       the notation $SRCIPADDRESSES[@1] and $DSTPORTS[@1], would result in
 366       parallel access to both lists and result in the following combinations:
 367     </p>
 368 <pre>
 369 10.0.0.1, 80
 370 11.1.2.3, 8080
 371 </pre>
 372     <p>
 373       Further, the notation of $VARIABLE is short-hand for $VARIABLE[@0]. The
 374       former notation always assumes the iterator with Id '0'.
 375     </p>
 376
 377     <h3><a id="nwfelemsRulesAdvIPAddrDetection">Automatic IP address detection</a></h3>
 378     <p>
 379        The detection of IP addresses used on a virtual machine's interface
 380        is automatically activated if the variable <code>IP</code> is referenced
 381        but no value has been assigned to it.
 382        <span class="since">Since 0.9.13</span>
 383        the variable <code>CTRL_IP_LEARNING</code> can be used to specify
 384        the IP address learning method to use. Valid values are <code>any</code>,
 385        <code>dhcp</code>, or <code>none</code>.
 386        <br/><br/>
 387        The value <code>any</code> means that libvirt may use any packet to
 388        determine the address in use by a virtual machine, which is the default
 389        behavior if the variable <code>CTRL_IP_LEARNING</code> is not set. This method
 390        will only detect a single IP address on an interface.
 391        Once a VM's IP address has been detected, its IP network traffic
 392        will be locked to that address, if for example IP address spoofing
 393        is prevented by one of its filters. In that case the user of the VM
 394        will not be able to change the IP address on the interface inside
 395        the VM, which would be considered IP address spoofing.
 396        When a VM is migrated to another host or resumed after a suspend operation,
 397        the first packet sent by the VM will again determine the IP address it can
 398        use on a particular interface.
 399        <br/>
 400        A value of <code>dhcp</code> specifies that libvirt should only honor DHCP
 401        server-assigned addresses with valid leases. This method supports the detection
 402        and usage of multiple IP address per interface.
 403        When a VM is resumed after a suspend operation, still valid IP address leases
 404        are applied to its filters. Otherwise the VM is expected to again use DHCP to obtain new
 405        IP addresses. The migration of a VM to another physical host requires that
 406        the VM again runs the DHCP protocol.
 407        <br/><br/>
 408        Use of <code>CTRL_IP_LEARNING=dhcp</code> (DHCP snooping) provides additional
 409        anti-spoofing security, especially when combined with a filter allowing
 410        only trusted DHCP servers to assign addresses. To enable this, set the
 411        variable <code>DHCPSERVER</code> to the IP address of a valid DHCP server
 412        and provide filters that use this variable to filter incoming DHCP responses.
 413        <br/><br/>
 414        When DHCP snooping is enabled and the DHCP lease expires,
 415        the VM will no longer be able to use the IP address until it acquires a
 416        new, valid lease from a DHCP server. If the VM is migrated, it must get
 417        a new valid DHCP lease to use an IP address (e.g., by
 418        bringing the VM interface down and up again).
 419        <br/><br/>
 420        Note that automatic DHCP detection listens to the DHCP traffic
 421        the VM exchanges with the DHCP server of the infrastructure. To avoid
 422        denial-of-service attacks on libvirt, the evaluation of those packets
 423        is rate-limited, meaning that a VM sending an excessive number of DHCP
 424        packets per second on an interface will not have all of those packets
 425        evaluated and thus filters may not get adapted. Normal DHCP client
 426        behavior is assumed to send a low number of DHCP packets per second.
 427        Further, it is important to setup appropriate filters on all VMs in
 428        the infrastructure to avoid them  being able to send DHCP
 429        packets. Therefore VMs must either be prevented from sending UDP and TCP
 430        traffic from port 67 to port 68 or the <code>DHCPSERVER</code>
 431        variable should be used on all VMs to restrict DHCP server messages to
 432        only be allowed to originate from trusted DHCP servers. At the same
 433        time anti-spoofing prevention must be enabled on all VMs in the subnet.
 434        <br/><br/>
 435        If <code>CTRL_IP_LEARNING</code> is set to <code>none</code>, libvirt does not do
 436        IP address learning and referencing <code>IP</code> without assigning it an
 437        explicit value is an error.
 438        <br/><br/>
 439        The following XML provides an example for the activation of IP address learning
 440        using the DHCP snooping method:
 441     </p>
 442 <pre>
 443 &lt;interface type='bridge'&gt;
 444   &lt;source bridge='virbr0'/&gt;
 445   &lt;filterref filter='clean-traffic'&gt;
 446     &lt;parameter name='CTRL_IP_LEARNING' value='dhcp'/&gt;
 447   &lt;/filterref&gt;
 448 &lt;/interface&gt;
 449 </pre>
 450
 451     <h3><a id="nwfelemsReservedVars">Reserved Variables</a></h3>
 452     <p>
 453       The following table lists reserved variables in use by libvirt.
 454     </p>
 455       <table class="top_table">
 456        <tr>
 457          <th> Variable Name </th>
 458          <th> Semantics </th>
 459        </tr>
 460        <tr>
 461          <td> MAC </td>
 462          <td> The MAC address of the interface </td>
 463        </tr>
 464        <tr>
 465          <td> IP </td>
 466          <td> The list of IP addresses in use by an interface </td>
 467        </tr>
 468        <tr>
 469          <td> IPV6 </td>
 470          <td> Not currently implemented:
 471               the list of IPV6 addresses in use by an interface </td>
 472        </tr>
 473        <tr>
 474          <td> DHCPSERVER </td>
 475          <td> The list of IP addresses of trusted DHCP servers</td>
 476        </tr>
 477        <tr>
 478          <td> DHCPSERVERV6 </td>
 479          <td> Not currently implemented:
 480               The list of IPv6 addresses of trusted DHCP servers</td>
 481        </tr>
 482        <tr>
 483          <td> CTRL_IP_LEARNING </td>
 484          <td> The choice of the IP address detection mode </td>
 485        </tr>
 486       </table>
 487
 488     <h2><a id="nwfelems">Element and attribute overview</a></h2>
 489
 490     <p>
 491       The root element required for all network filters is
 492       named <code>filter</code> with two possible attributes. The
 493       <code>name</code> attribute provides a unique name of the
 494       given filter. The <code>chain</code> attribute is optional but
 495       allows certain filters to be better organized for more efficient
 496       processing by the firewall subsystem of the underlying host.
 497       Currently the system only supports the chains <code>root,
 498       ipv4, ipv6, arp and rarp</code>.
 499     </p>
 500
 501     <h3><a id="nwfelemsRefs">References to other filters</a></h3>
 502     <p>
 503      Any filter may hold references to other filters. Individual
 504      filters may be referenced multiple times in a filter tree but
 505      references between filters must not introduce loops (directed
 506      acyclic graph).
 507      <br/><br/>
 508      The following shows the XML of the <code>clean-traffic</code>
 509      network filter referencing several other filters.
 510     </p>
 511 <pre>
 512 &lt;filter name='clean-traffic'&gt;
 513   &lt;uuid&gt;6ef53069-ba34-94a0-d33d-17751b9b8cb1&lt;/uuid&gt;
 514   &lt;filterref filter='no-mac-spoofing'/&gt;
 515   &lt;filterref filter='no-ip-spoofing'/&gt;
 516   &lt;filterref filter='allow-incoming-ipv4'/&gt;
 517   &lt;filterref filter='no-arp-spoofing'/&gt;
 518   &lt;filterref filter='no-other-l2-traffic'/&gt;
 519   &lt;filterref filter='qemu-announce-self'/&gt;
 520 &lt;/filter&gt;
 521 </pre>
 522
 523     <p>
 524     To reference another filter, the XML node <code>filterref</code>
 525     needs to be provided inside a <code>filter</code> node. This
 526     node must have the attribute <code>filter</code> whose value contains
 527     the name of the filter to be referenced.
 528     <br/><br/>
 529     New network filters can be defined at any time and
 530     may contain references to network filters that are
 531     not known to libvirt, yet. However, once a virtual machine
 532     is started or a network interface
 533     referencing a filter is to be hotplugged, all network filters
 534     in the filter tree must be available. Otherwise the virtual
 535     machine will not start or the network interface cannot be
 536     attached.
 537     </p>
 538
 539     <h3><a id="nwfelemsRules">Filter rules</a></h3>
 540     <p>
 541     The following XML shows a simple example of a network
 542     traffic filter implementing a rule to drop traffic if
 543     the IP address (provided through the value of the
 544     variable IP) in an outgoing IP packet is not the expected
 545     one, thus preventing IP address spoofing by the VM.
 546     </p>
 547 <pre>
 548 &lt;filter name='no-ip-spoofing' chain='ipv4'&gt;
 549   &lt;uuid&gt;fce8ae33-e69e-83bf-262e-30786c1f8072&lt;/uuid&gt;
 550   &lt;rule action='drop' direction='out' priority='500'&gt;
 551     &lt;ip match='no' srcipaddr='$IP'/&gt;
 552   &lt;/rule&gt;
 553 &lt;/filter&gt;
 554 </pre>
 555
 556     <p>
 557      A traffic filtering rule starts with the <code>rule</code>
 558      node. This node may contain up to three attributes
 559     </p>
 560     <ul>
 561      <li>
 562         action -- mandatory; must either be <code>drop</code>
 563         (matching the rule silently discards the packet with no
 564         further analysis),
 565         <code>reject</code> (matching the rule generates an ICMP
 566         reject message with no further analysis) <span class="since">(since
 567         0.9.0)</span>, <code>accept</code> (matching the rule accepts
 568         the packet with no further analysis), <code>return</code>
 569         (matching the rule passes this filter, but returns control to
 570         the calling filter for further
 571         analysis) <span class="since">(since 0.9.7)</span>,
 572         or <code>continue</code> (matching the rule goes on to the next
 573         rule for further analysis) <span class="since">(since
 574         0.9.7)</span>.
 575      </li>
 576      <li>
 577         direction -- mandatory; must either be <code>in</code>, <code>out</code> or
 578          <code>inout</code> if the rule is for incoming,
 579          outgoing or incoming-and-outgoing traffic
 580      </li>
 581      <li>
 582         priority -- optional; the priority of the rule controls the order in
 583         which the rule will be instantiated relative to other rules.
 584         Rules with lower value will be instantiated before rules with higher
 585         values.
 586         Valid values are in the range of 0 to 1000.
 587         <span class="since">Since 0.9.8</span> this has been extended to cover
 588         the range of -1000 to 1000. If this attribute is not
 589         provided, priority 500 will automatically be assigned.
 590         <br/>
 591         Note that filtering rules in the <code>root</code> chain are sorted
 592         with filters connected to the <code>root</code> chain following
 593         their priorities. This allows to interleave filtering rules with
 594         access to filter chains.
 595         (See also section on
 596          <a href="#nwfconceptschainpriorities">
 597            filtering chain priorities
 598          </a>.)
 599      </li>
 600      <li>
 601         statematch -- optional; possible values are '0' or 'false' to
 602         turn the underlying connection state matching off; default is 'true'
 603         <br/>
 604         Also read the section on <a href="#nwfelemsRulesAdv">advanced configuration</a>
 605         topics.
 606      </li>
 607     </ul>
 608     <p>
 609      The above example indicates that the traffic of type <code>ip</code>
 610      will be associated with the chain 'ipv4' and the rule will have
 611      priority 500. If for example another filter is referenced whose
 612      traffic of type <code>ip</code> is also associated with the chain
 613      'ipv4' then that filter's rules will be ordered relative to the priority
 614      500 of the shown rule.
 615      <br/><br/>
 616      A rule may contain a single rule for filtering of traffic. The
 617      above example shows that traffic of type <code>ip</code> is to be
 618      filtered.
 619     </p>
 620
 621     <h4><a id="nwfelemsRulesProto">Supported protocols</a></h4>
 622     <p>
 623      The following sections enumerate the list of protocols that
 624      are supported by the network filtering subsystem. The
 625      type of traffic a rule is supposed to filter on is provided
 626      in the <code>rule</code> node as a nested node. Depending
 627      on the traffic type a rule is filtering, the attributes are
 628      different. The above example showed the single
 629      attribute <code>srcipaddr</code> that is valid inside the
 630      <code>ip</code> traffic filtering node. The following sections
 631      show what attributes are valid and what type of data they are
 632      expecting. The following datatypes are available:
 633     </p>
 634     <ul>
 635      <li>UINT8 : 8 bit integer; range 0-255</li>
 636      <li>UINT16: 16 bit integer; range 0-65535</li>
 637      <li>MAC_ADDR: MAC address in dotted decimal format, i.e., 00:11:22:33:44:55</li>
 638      <li>MAC_MASK: MAC address mask in MAC address format, i.e., FF:FF:FF:FC:00:00</li>
 639      <li>IP_ADDR: IP address in dotted decimal format, i.e., 10.1.2.3</li>
 640      <li>IP_MASK: IP address mask in either dotted decimal format (255.255.248.0) or CIDR mask (0-32)</li>
 641      <li>IPV6_ADDR: IPv6 address in numbers format, i.e., FFFF::1</li>
 642      <li>IPV6_MASK: IPv6 mask in numbers format (FFFF:FFFF:FC00::) or CIDR mask (0-128)</li>
 643      <li>STRING: A string</li>
 644      <li>BOOLEAN: 'true', 'yes', '1' or 'false', 'no', '0'</li>
 645      <li>IPSETFLAGS: The source and destination flags of the ipset described
 646          by up to 6 'src' or 'dst' elements selecting features from either
 647          the source or destination part of the packet header; example:
 648          src,src,dst. The number of 'selectors' to provide here depends
 649          on the type of ipset that is referenced.</li>
 650     </ul>
 651     <p>
 652      <br/><br/>
 653      Every attribute except for those of type IP_MASK or IPV6_MASK can
 654      be negated using the <code>match</code>
 655      attribute with value <code>no</code>. Multiple negated attributes
 656      may be grouped together. The following
 657      XML fragment shows such an example using abstract attributes.
 658     </p>
 659 <pre>
 660 [...]
 661 &lt;rule action='drop' direction='in'&gt;
 662   &lt;protocol match='no' attribute1='value1' attribute2='value2'/&gt;
 663   &lt;protocol attribute3='value3'/&gt;
 664 &lt;/rule&gt;
 665 [...]
 666 </pre>
 667     <p>
 668      Rules perform a logical AND evaluation on all values of the given
 669      protocol attributes. Thus, if a single attribute's value does not match
 670      the one given in the rule, the whole rule will be skipped during
 671      evaluation. Therefore, in the above example incoming traffic
 672      will only be dropped if
 673      the protocol property attribute1 does not match value1 AND
 674      the protocol property attribute2 does not match value2 AND
 675      the protocol property attribute3 matches value3.
 676      <br/><br/>
 677     </p>
 678
 679
 680     <h5><a id="nwfelemsRulesProtoMAC">MAC (Ethernet)</a></h5>
 681     <p>
 682       Protocol ID: <code>mac</code>
 683       <br/>
 684       Note: Rules of this type should go into the <code>root</code> chain.
 685     </p>
 686       <table class="top_table">
 687        <tr>
 688          <th> Attribute </th>
 689          <th> Datatype </th>
 690          <th> Semantics </th>
 691        </tr>
 692        <tr>
 693          <td>srcmacaddr</td>
 694          <td>MAC_ADDR</td>
 695          <td>MAC address of sender</td>
 696        </tr>
 697        <tr>
 698          <td>srcmacmask</td>
 699          <td>MAC_MASK</td>
 700          <td>Mask applied to MAC address of sender</td>
 701        </tr>
 702        <tr>
 703          <td>dstmacaddr</td>
 704          <td>MAC_ADDR</td>
 705          <td>MAC address of destination</td>
 706        </tr>
 707        <tr>
 708          <td>dstmacmask</td>
 709          <td>MAC_MASK</td>
 710          <td>Mask applied to MAC address of destination</td>
 711        </tr>
 712        <tr>
 713          <td>protocolid</td>
 714          <td>UINT16 (0x600-0xffff), STRING</td>
 715          <td>Layer 3 protocol ID</td>
 716        </tr>
 717        <tr>
 718          <td>comment <span class="since">(Since 0.8.5)</span></td>
 719          <td>STRING</td>
 720          <td>text with max. 256 characters</td>
 721        </tr>
 722       </table>
 723     <p>
 724       Valid Strings for <code>protocolid</code> are: arp, rarp, ipv4, ipv6
 725     </p>
 726 <pre>
 727 [...]
 728 &lt;mac match='no' srcmacaddr='$MAC'/&gt;
 729 [...]
 730 </pre>
 731
 732     <h5><a id="nwfelemsRulesProtoVLAN">VLAN (802.1Q)</a>
 733       <span class="since">(Since 0.9.8)</span>
 734     </h5>
 735     <p>
 736       Protocol ID: <code>vlan</code>
 737       <br/>
 738       Note: Rules of this type should go either into the <code>root</code> or
 739       <code>vlan</code> chain.
 740     </p>
 741       <table class="top_table">
 742        <tr>
 743          <th> Attribute </th>
 744          <th> Datatype </th>
 745          <th> Semantics </th>
 746        </tr>
 747        <tr>
 748          <td>srcmacaddr</td>
 749          <td>MAC_ADDR</td>
 750          <td>MAC address of sender</td>
 751        </tr>
 752        <tr>
 753          <td>srcmacmask</td>
 754          <td>MAC_MASK</td>
 755          <td>Mask applied to MAC address of sender</td>
 756        </tr>
 757        <tr>
 758          <td>dstmacaddr</td>
 759          <td>MAC_ADDR</td>
 760          <td>MAC address of destination</td>
 761        </tr>
 762        <tr>
 763          <td>dstmacmask</td>
 764          <td>MAC_MASK</td>
 765          <td>Mask applied to MAC address of destination</td>
 766        </tr>
 767        <tr>
 768          <td>vlanid</td>
 769          <td>UINT16 (0x0-0xfff, 0 - 4095)</td>
 770          <td>VLAN ID</td>
 771        </tr>
 772        <tr>
 773          <td>encap-protocol</td>
 774          <td>UINT16 (0x03c-0xfff), String</td>
 775          <td>Encapsulated layer 3 protocol ID</td>
 776        </tr>
 777        <tr>
 778          <td>comment </td>
 779          <td>STRING</td>
 780          <td>text with max. 256 characters</td>
 781        </tr>
 782       </table>
 783     <p>
 784       Valid Strings for <code>encap-protocol</code> are: arp, ipv4, ipv6
 785     </p>
 786
 787     <h5><a id="nwfelemsRulesProtoSTP">STP (Spanning Tree Protocol)</a>
 788       <span class="since">(Since 0.9.8)</span>
 789     </h5>
 790     <p>
 791       Protocol ID: <code>stp</code>
 792       <br/>
 793       Note: Rules of this type should go either into the <code>root</code> or
 794       <code>stp</code> chain.
 795     </p>
 796       <table class="top_table">
 797        <tr>
 798          <th> Attribute </th>
 799          <th> Datatype </th>
 800          <th> Semantics </th>
 801        </tr>
 802        <tr>
 803          <td>srcmacaddr</td>
 804          <td>MAC_ADDR</td>
 805          <td>MAC address of sender</td>
 806        </tr>
 807        <tr>
 808          <td>srcmacmask</td>
 809          <td>MAC_MASK</td>
 810          <td>Mask applied to MAC address of sender</td>
 811        </tr>
 812        <tr>
 813          <td>type</td>
 814          <td>UINT8</td>
 815          <td>Bridge Protocol Data Unit (BPDU) type</td>
 816        </tr>
 817        <tr>
 818          <td>flags</td>
 819          <td>UINT8</td>
 820          <td>BPDU flag</td>
 821        </tr>
 822        <tr>
 823          <td>root-priority</td>
 824          <td>UINT16</td>
 825          <td>Root priority (range start)</td>
 826        </tr>
 827        <tr>
 828          <td>root-priority-hi</td>
 829          <td>UINT16</td>
 830          <td>Root priority range end</td>
 831        </tr>
 832        <tr>
 833          <td>root-address</td>
 834          <td>MAC_ADDRESS</td>
 835          <td>Root MAC address</td>
 836        </tr>
 837        <tr>
 838          <td>root-address-mask</td>
 839          <td>MAC_MASK</td>
 840          <td>Root MAC address mask</td>
 841        </tr>
 842        <tr>
 843          <td>root-cost</td>
 844          <td>UINT32</td>
 845          <td>Root path cost (range start)</td>
 846        </tr>
 847        <tr>
 848          <td>root-cost-hi</td>
 849          <td>UINT32</td>
 850          <td>Root path cost range end</td>
 851        </tr>
 852        <tr>
 853          <td>sender-priority</td>
 854          <td>UINT16</td>
 855          <td>Sender priority (range start)</td>
 856        </tr>
 857        <tr>
 858          <td>sender-priority-hi</td>
 859          <td>UINT16</td>
 860          <td>Sender priority range end</td>
 861        </tr>
 862        <tr>
 863          <td>sender-address</td>
 864          <td>MAC_ADDRESS</td>
 865          <td>BPDU sender MAC address</td>
 866        </tr>
 867        <tr>
 868          <td>sender-address-mask</td>
 869          <td>MAC_MASK</td>
 870          <td>BPDU sender MAC address mask</td>
 871        </tr>
 872        <tr>
 873          <td>port</td>
 874          <td>UINT16</td>
 875          <td>Port identifier (range start)</td>
 876        </tr>
 877        <tr>
 878          <td>port_hi</td>
 879          <td>UINT16</td>
 880          <td>Port identifier range end</td>
 881        </tr>
 882        <tr>
 883          <td>msg-age</td>
 884          <td>UINT16</td>
 885          <td>Message age timer (range start)</td>
 886        </tr>
 887        <tr>
 888          <td>msg-age-hi</td>
 889          <td>UINT16</td>
 890          <td>Message age timer range end</td>
 891        </tr>
 892        <tr>
 893          <td>max-age</td>
 894          <td>UINT16</td>
 895          <td>Maximum age timer (range start)</td>
 896        </tr>
 897        <tr>
 898          <td>max-age-hi</td>
 899          <td>UINT16</td>
 900          <td>Maximum age timer range end</td>
 901        </tr>
 902        <tr>
 903          <td>hello-time</td>
 904          <td>UINT16</td>
 905          <td>Hello time timer (range start)</td>
 906        </tr>
 907        <tr>
 908          <td>hello-time-hi</td>
 909          <td>UINT16</td>
 910          <td>Hello time timer range end</td>
 911        </tr>
 912        <tr>
 913          <td>forward-delay</td>
 914          <td>UINT16</td>
 915          <td>Forward delay (range start)</td>
 916        </tr>
 917        <tr>
 918          <td>forward-delay-hi</td>
 919          <td>UINT16</td>
 920          <td>Forward delay range end</td>
 921        </tr>
 922        <tr>
 923          <td>comment</td>
 924          <td>STRING</td>
 925          <td>text with max. 256 characters</td>
 926        </tr>
 927       </table>
 928
 929     <h5><a id="nwfelemsRulesProtoARP">ARP/RARP</a></h5>
 930     <p>
 931       Protocol ID: <code>arp</code> or <code>rarp</code>
 932       <br/>
 933       Note: Rules of this type should either go into the
 934       <code>root</code> or <code>arp/rarp</code> chain.
 935     </p>
 936       <table class="top_table">
 937        <tr>
 938          <th> Attribute </th>
 939          <th> Datatype </th>
 940          <th> Semantics </th>
 941        </tr>
 942        <tr>
 943          <td>srcmacaddr</td>
 944          <td>MAC_ADDR</td>
 945          <td>MAC address of sender</td>
 946        </tr>
 947        <tr>
 948          <td>srcmacmask</td>
 949          <td>MAC_MASK</td>
 950          <td>Mask applied to MAC address of sender</td>
 951        </tr>
 952        <tr>
 953          <td>dstmacaddr</td>
 954          <td>MAC_ADDR</td>
 955          <td>MAC address of destination</td>
 956        </tr>
 957        <tr>
 958          <td>dstmacmask</td>
 959          <td>MAC_MASK</td>
 960          <td>Mask applied to MAC address of destination</td>
 961        </tr>
 962        <tr>
 963          <td>hwtype</td>
 964          <td>UINT16</td>
 965          <td>Hardware type</td>
 966        </tr>
 967        <tr>
 968          <td>protocoltype</td>
 969          <td>UINT16</td>
 970          <td>Protocol type</td>
 971        </tr>
 972        <tr>
 973          <td>opcode</td>
 974          <td>UINT16, STRING</td>
 975          <td>Opcode</td>
 976        </tr>
 977        <tr>
 978          <td>arpsrcmacaddr</td>
 979          <td>MAC_ADDR</td>
 980          <td>Source MAC address in ARP/RARP packet</td>
 981        </tr>
 982        <tr>
 983          <td>arpdstmacaddr</td>
 984          <td>MAC_ADDR</td>
 985          <td>Destination MAC address in ARP/RARP packet</td>
 986        </tr>
 987        <tr>
 988          <td>arpsrcipaddr</td>
 989          <td>IP_ADDR</td>
 990          <td>Source IP address in ARP/RARP packet</td>
 991        </tr>
 992        <tr>
 993          <td>arpsrcipmask <span class="since">(Since 1.2.3)</span></td>
 994          <td>IP_MASK</td>
 995          <td>Source IP mask</td>
 996        </tr>
 997        <tr>
 998          <td>arpdstipaddr</td>
 999          <td>IP_ADDR</td>
1000          <td>Destination IP address in ARP/RARP packet</td>
1001        </tr>
1002        <tr>
1003          <td>arpdstipmask <span class="since">(Since 1.2.3)</span></td>
1004          <td>IP_MASK</td>
1005          <td>Destination IP mask</td>
1006        </tr>
1007        <tr>
1008          <td>comment <span class="since">(Since 0.8.5)</span></td>
1009          <td>STRING</td>
1010          <td>text with max. 256 characters</td>
1011        </tr>
1012        <tr>
1013          <td>gratuitous <span class="since">(Since 0.9.2)</span></td>
1014          <td>BOOLEAN</td>
1015          <td>boolean indicating whether to check for gratuitous ARP packet</td>
1016        </tr>
1017       </table>
1018     <p>
1019       Valid strings for the <code>Opcode</code> field are:
1020        Request, Reply, Request_Reverse, Reply_Reverse, DRARP_Request,
1021        DRARP_Reply, DRARP_Error, InARP_Request, ARP_NAK
1022       <br/><br/>
1023     </p>
1024
1025     <h5><a id="nwfelemsRulesProtoIP">IPv4</a></h5>
1026     <p>
1027       Protocol ID: <code>ip</code>
1028       <br/>
1029       Note: Rules of this type should either go into the
1030       <code>root</code> or <code>ipv4</code> chain.
1031     </p>
1032       <table class="top_table">
1033        <tr>
1034          <th> Attribute </th>
1035          <th> Datatype </th>
1036          <th> Semantics </th>
1037        </tr>
1038        <tr>
1039          <td>srcmacaddr</td>
1040          <td>MAC_ADDR</td>
1041          <td>MAC address of sender</td>
1042        </tr>
1043        <tr>
1044          <td>srcmacmask</td>
1045          <td>MAC_MASK</td>
1046          <td>Mask applied to MAC address of sender</td>
1047        </tr>
1048        <tr>
1049          <td>dstmacaddr</td>
1050          <td>MAC_ADDR</td>
1051          <td>MAC address of destination</td>
1052        </tr>
1053        <tr>
1054          <td>dstmacmask</td>
1055          <td>MAC_MASK</td>
1056          <td>Mask applied to MAC address of destination</td>
1057        </tr>
1058        <tr>
1059          <td>srcipaddr</td>
1060          <td>IP_ADDR</td>
1061          <td>Source IP address</td>
1062        </tr>
1063        <tr>
1064          <td>srcipmask</td>
1065          <td>IP_MASK</td>
1066          <td>Mask applied to source IP address</td>
1067        </tr>
1068        <tr>
1069          <td>dstipaddr</td>
1070          <td>IP_ADDR</td>
1071          <td>Destination IP address</td>
1072        </tr>
1073        <tr>
1074          <td>dstipmask</td>
1075          <td>IP_MASK</td>
1076          <td>Mask applied to destination IP address</td>
1077        </tr>
1078        <tr>
1079          <td>protocol</td>
1080          <td>UINT8, STRING</td>
1081          <td>Layer 4 protocol identifier</td>
1082        </tr>
1083        <tr>
1084          <td>srcportstart</td>
1085          <td>UINT16</td>
1086          <td>Start of range of valid source ports; requires <code>protocol</code></td>
1087        </tr>
1088        <tr>
1089          <td>srcportend</td>
1090          <td>UINT16</td>
1091          <td>End of range of valid source ports; requires <code>protocol</code></td>
1092        </tr>
1093        <tr>
1094          <td>dstportstart</td>
1095          <td>UINT16</td>
1096          <td>Start of range of valid destination ports; requires <code>protocol</code></td>
1097        </tr>
1098        <tr>
1099          <td>dstportend</td>
1100          <td>UINT16</td>
1101          <td>End of range of valid destination ports; requires <code>protocol</code></td>
1102        </tr>
1103        <tr>
1104          <td>dscp</td>
1105          <td>UINT8 (0x0-0x3f, 0 - 63)</td>
1106          <td>Differentiated Services Code Point</td>
1107        </tr>
1108        <tr>
1109          <td>comment <span class="since">(Since 0.8.5)</span></td>
1110          <td>STRING</td>
1111          <td>text with max. 256 characters</td>
1112        </tr>
1113       </table>
1114     <p>
1115       Valid strings for <code>protocol</code> are:
1116          tcp, udp, udplite, esp, ah, icmp, igmp, sctp
1117       <br/><br/>
1118     </p>
1119
1120
1121     <h5><a id="nwfelemsRulesProtoIPv6">IPv6</a></h5>
1122     <p>
1123       Protocol ID: <code>ipv6</code>
1124       <br/>
1125       Note: Rules of this type should either go into the
1126       <code>root</code> or <code>ipv6</code> chain.
1127     </p>
1128       <table class="top_table">
1129        <tr>
1130          <th> Attribute </th>
1131          <th> Datatype </th>
1132          <th> Semantics </th>
1133        </tr>
1134        <tr>
1135          <td>srcmacaddr</td>
1136          <td>MAC_ADDR</td>
1137          <td>MAC address of sender</td>
1138        </tr>
1139        <tr>
1140          <td>srcmacmask</td>
1141          <td>MAC_MASK</td>
1142          <td>Mask applied to MAC address of sender</td>
1143        </tr>
1144        <tr>
1145          <td>dstmacaddr</td>
1146          <td>MAC_ADDR</td>
1147          <td>MAC address of destination</td>
1148        </tr>
1149        <tr>
1150          <td>dstmacmask</td>
1151          <td>MAC_MASK</td>
1152          <td>Mask applied to MAC address of destination</td>
1153        </tr>
1154        <tr>
1155          <td>srcipaddr</td>
1156          <td>IPV6_ADDR</td>
1157          <td>Source IPv6 address</td>
1158        </tr>
1159        <tr>
1160          <td>srcipmask</td>
1161          <td>IPV6_MASK</td>
1162          <td>Mask applied to source IPv6 address</td>
1163        </tr>
1164        <tr>
1165          <td>dstipaddr</td>
1166          <td>IPV6_ADDR</td>
1167          <td>Destination IPv6 address</td>
1168        </tr>
1169        <tr>
1170          <td>dstipmask</td>
1171          <td>IPV6_MASK</td>
1172          <td>Mask applied to destination IPv6 address</td>
1173        </tr>
1174        <tr>
1175          <td>protocol</td>
1176          <td>UINT8</td>
1177          <td>Layer 4 protocol identifier</td>
1178        </tr>
1179        <tr>
1180          <td>srcportstart</td>
1181          <td>UINT16</td>
1182          <td>Start of range of valid source ports; requires <code>protocol</code></td>
1183        </tr>
1184        <tr>
1185          <td>srcportend</td>
1186          <td>UINT16</td>
1187          <td>End of range of valid source ports; requires <code>protocol</code></td>
1188        </tr>
1189        <tr>
1190          <td>dstportstart</td>
1191          <td>UINT16</td>
1192          <td>Start of range of valid destination ports; requires <code>protocol</code></td>
1193        </tr>
1194        <tr>
1195          <td>dstportend</td>
1196          <td>UINT16</td>
1197          <td>End of range of valid destination ports; requires <code>protocol</code></td>
1198        </tr>
1199        <tr>
1200          <td>type<span class="since">(Since 1.2.12)</span></td>
1201          <td>UINT8</td>
1202          <td>ICMPv6 type; requires <code>protocol</code> to be set to <code>icmpv6</code></td>
1203        </tr>
1204        <tr>
1205          <td>typeend<span class="since">(Since 1.2.12)</span></td>
1206          <td>UINT8</td>
1207          <td>ICMPv6 type end of range; requires <code>protocol</code> to be set to <code>icmpv6</code></td>
1208        </tr>
1209        <tr>
1210          <td>code<span class="since">(Since 1.2.12)</span></td>
1211          <td>UINT8</td>
1212          <td>ICMPv6 code; requires <code>protocol</code> to be set to <code>icmpv6</code></td>
1213        </tr>
1214        <tr>
1215          <td>code<span class="since">(Since 1.2.12)</span></td>
1216          <td>UINT8</td>
1217          <td>ICMPv6 code end of range; requires <code>protocol</code> to be set to <code>icmpv6</code></td>
1218        </tr>
1219        <tr>
1220          <td>comment <span class="since">(Since 0.8.5)</span></td>
1221          <td>STRING</td>
1222          <td>text with max. 256 characters</td>
1223        </tr>
1224       </table>
1225     <p>
1226       Valid strings for <code>protocol</code> are:
1227          tcp, udp, udplite, esp, ah, icmpv6, sctp
1228       <br/><br/>
1229     </p>
1230
1231     <h5><a id="nwfelemsRulesProtoTCP-ipv4">TCP/UDP/SCTP</a></h5>
1232     <p>
1233       Protocol ID: <code>tcp</code>, <code>udp</code>, <code>sctp</code>
1234       <br/>
1235       Note: The chain parameter is ignored for this type of traffic
1236       and should either be omitted or set to <code>root</code>.
1237     </p>
1238       <table class="top_table">
1239        <tr>
1240          <th> Attribute </th>
1241          <th> Datatype </th>
1242          <th> Semantics </th>
1243        </tr>
1244        <tr>
1245          <td>srcmacaddr</td>
1246          <td>MAC_ADDR</td>
1247          <td>MAC address of sender</td>
1248        </tr>
1249        <tr>
1250          <td>srcipaddr</td>
1251          <td>IP_ADDR</td>
1252          <td>Source IP address</td>
1253        </tr>
1254        <tr>
1255          <td>srcipmask</td>
1256          <td>IP_MASK</td>
1257          <td>Mask applied to source IP address</td>
1258        </tr>
1259        <tr>
1260          <td>dstipaddr</td>
1261          <td>IP_ADDR</td>
1262          <td>Destination IP address</td>
1263        </tr>
1264        <tr>
1265          <td>dstipmask</td>
1266          <td>IP_MASK</td>
1267          <td>Mask applied to destination IP address</td>
1268        </tr>
1269
1270        <tr>
1271          <td>srcipfrom</td>
1272          <td>IP_ADDR</td>
1273          <td>Start of range of source IP address</td>
1274        </tr>
1275        <tr>
1276          <td>srcipto</td>
1277          <td>IP_ADDR</td>
1278          <td>End of range of source IP address</td>
1279        </tr>
1280        <tr>
1281          <td>dstipfrom</td>
1282          <td>IP_ADDR</td>
1283          <td>Start of range of destination IP address</td>
1284        </tr>
1285        <tr>
1286          <td>dstipto</td>
1287          <td>IP_ADDR</td>
1288          <td>End of range of destination IP address</td>
1289        </tr>
1290
1291        <tr>
1292          <td>srcportstart</td>
1293          <td>UINT16</td>
1294          <td>Start of range of valid source ports</td>
1295        </tr>
1296        <tr>
1297          <td>srcportend</td>
1298          <td>UINT16</td>
1299          <td>End of range of valid source ports</td>
1300        </tr>
1301        <tr>
1302          <td>dstportstart</td>
1303          <td>UINT16</td>
1304          <td>Start of range of valid destination ports</td>
1305        </tr>
1306        <tr>
1307          <td>dstportend</td>
1308          <td>UINT16</td>
1309          <td>End of range of valid destination ports</td>
1310        </tr>
1311        <tr>
1312          <td>dscp</td>
1313          <td>UINT8 (0x0-0x3f, 0 - 63)</td>
1314          <td>Differentiated Services Code Point</td>
1315        </tr>
1316        <tr>
1317          <td>comment <span class="since">(Since 0.8.5)</span></td>
1318          <td>STRING</td>
1319          <td>text with max. 256 characters</td>
1320        </tr>
1321        <tr>
1322          <td>state <span class="since">(Since 0.8.5)</span></td>
1323          <td>STRING</td>
1324          <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
1325        </tr>
1326        <tr>
1327          <td>flags <span class="since">(Since 0.9.1)</span></td>
1328          <td>STRING</td>
1329          <td>TCP-only: format of mask/flags with mask and flags each being a comma separated list of SYN,ACK,URG,PSH,FIN,RST or NONE or ALL</td>
1330        </tr>
1331        <tr>
1332          <td>ipset <span class="since">(Since 0.9.13)</span></td>
1333          <td>STRING</td>
1334          <td>The name of an IPSet managed outside of libvirt</td>
1335        </tr>
1336        <tr>
1337          <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
1338          <td>IPSETFLAGS</td>
1339          <td>flags for the IPSet; requires ipset attribute</td>
1340        </tr>
1341       </table>
1342     <p>
1343       <br/><br/>
1344     </p>
1345
1346
1347     <h5><a id="nwfelemsRulesProtoICMP">ICMP</a></h5>
1348     <p>
1349       Protocol ID: <code>icmp</code>
1350       <br/>
1351       Note: The chain parameter is ignored for this type of traffic
1352       and should either be omitted or set to <code>root</code>.
1353     </p>
1354       <table class="top_table">
1355        <tr>
1356          <th> Attribute </th>
1357          <th> Datatype </th>
1358          <th> Semantics </th>
1359        </tr>
1360        <tr>
1361          <td>srcmacaddr</td>
1362          <td>MAC_ADDR</td>
1363          <td>MAC address of sender</td>
1364        </tr>
1365        <tr>
1366          <td>srcmacmask</td>
1367          <td>MAC_MASK</td>
1368          <td>Mask applied to MAC address of sender</td>
1369        </tr>
1370        <tr>
1371          <td>dstmacaddr</td>
1372          <td>MAC_ADDR</td>
1373          <td>MAC address of destination</td>
1374        </tr>
1375        <tr>
1376          <td>dstmacmask</td>
1377          <td>MAC_MASK</td>
1378          <td>Mask applied to MAC address of destination</td>
1379        </tr>
1380        <tr>
1381          <td>srcipaddr</td>
1382          <td>IP_ADDR</td>
1383          <td>Source IP address</td>
1384        </tr>
1385        <tr>
1386          <td>srcipmask</td>
1387          <td>IP_MASK</td>
1388          <td>Mask applied to source IP address</td>
1389        </tr>
1390        <tr>
1391          <td>dstipaddr</td>
1392          <td>IP_ADDR</td>
1393          <td>Destination IP address</td>
1394        </tr>
1395        <tr>
1396          <td>dstipmask</td>
1397          <td>IP_MASK</td>
1398          <td>Mask applied to destination IP address</td>
1399        </tr>
1400
1401        <tr>
1402          <td>srcipfrom</td>
1403          <td>IP_ADDR</td>
1404          <td>Start of range of source IP address</td>
1405        </tr>
1406        <tr>
1407          <td>srcipto</td>
1408          <td>IP_ADDR</td>
1409          <td>End of range of source IP address</td>
1410        </tr>
1411        <tr>
1412          <td>dstipfrom</td>
1413          <td>IP_ADDR</td>
1414          <td>Start of range of destination IP address</td>
1415        </tr>
1416        <tr>
1417          <td>dstipto</td>
1418          <td>IP_ADDR</td>
1419          <td>End of range of destination IP address</td>
1420        </tr>
1421        <tr>
1422          <td>type</td>
1423          <td>UINT16</td>
1424          <td>ICMP type</td>
1425        </tr>
1426        <tr>
1427          <td>code</td>
1428          <td>UINT16</td>
1429          <td>ICMP code</td>
1430        </tr>
1431        <tr>
1432          <td>dscp</td>
1433          <td>UINT8 (0x0-0x3f, 0 - 63)</td>
1434          <td>Differentiated Services Code Point</td>
1435        </tr>
1436        <tr>
1437          <td>comment <span class="since">(Since 0.8.5)</span></td>
1438          <td>STRING</td>
1439          <td>text with max. 256 characters</td>
1440        </tr>
1441        <tr>
1442          <td>state <span class="since">(Since 0.8.5)</span></td>
1443          <td>STRING</td>
1444          <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
1445        </tr>
1446        <tr>
1447          <td>ipset <span class="since">(Since 0.9.13)</span></td>
1448          <td>STRING</td>
1449          <td>The name of an IPSet managed outside of libvirt</td>
1450        </tr>
1451        <tr>
1452          <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
1453          <td>IPSETFLAGS</td>
1454          <td>flags for the IPSet; requires ipset attribute</td>
1455        </tr>
1456       </table>
1457     <p>
1458       <br/><br/>
1459     </p>
1460
1461     <h5><a id="nwfelemsRulesProtoMisc">IGMP, ESP, AH, UDPLITE, 'ALL'</a></h5>
1462     <p>
1463       Protocol ID: <code>igmp</code>, <code>esp</code>, <code>ah</code>, <code>udplite</code>, <code>all</code>
1464       <br/>
1465       Note: The chain parameter is ignored for this type of traffic
1466       and should either be omitted or set to <code>root</code>.
1467     </p>
1468       <table class="top_table">
1469        <tr>
1470          <th> Attribute </th>
1471          <th> Datatype </th>
1472          <th> Semantics </th>
1473        </tr>
1474        <tr>
1475          <td>srcmacaddr</td>
1476          <td>MAC_ADDR</td>
1477          <td>MAC address of sender</td>
1478        </tr>
1479        <tr>
1480          <td>srcmacmask</td>
1481          <td>MAC_MASK</td>
1482          <td>Mask applied to MAC address of sender</td>
1483        </tr>
1484        <tr>
1485          <td>dstmacaddr</td>
1486          <td>MAC_ADDR</td>
1487          <td>MAC address of destination</td>
1488        </tr>
1489        <tr>
1490          <td>dstmacmask</td>
1491          <td>MAC_MASK</td>
1492          <td>Mask applied to MAC address of destination</td>
1493        </tr>
1494        <tr>
1495          <td>srcipaddr</td>
1496          <td>IP_ADDR</td>
1497          <td>Source IP address</td>
1498        </tr>
1499        <tr>
1500          <td>srcipmask</td>
1501          <td>IP_MASK</td>
1502          <td>Mask applied to source IP address</td>
1503        </tr>
1504        <tr>
1505          <td>dstipaddr</td>
1506          <td>IP_ADDR</td>
1507          <td>Destination IP address</td>
1508        </tr>
1509        <tr>
1510          <td>dstipmask</td>
1511          <td>IP_MASK</td>
1512          <td>Mask applied to destination IP address</td>
1513        </tr>
1514
1515        <tr>
1516          <td>srcipfrom</td>
1517          <td>IP_ADDR</td>
1518          <td>Start of range of source IP address</td>
1519        </tr>
1520        <tr>
1521          <td>srcipto</td>
1522          <td>IP_ADDR</td>
1523          <td>End of range of source IP address</td>
1524        </tr>
1525        <tr>
1526          <td>dstipfrom</td>
1527          <td>IP_ADDR</td>
1528          <td>Start of range of destination IP address</td>
1529        </tr>
1530        <tr>
1531          <td>dstipto</td>
1532          <td>IP_ADDR</td>
1533          <td>End of range of destination IP address</td>
1534        </tr>
1535        <tr>
1536          <td>dscp</td>
1537          <td>UINT8 (0x0-0x3f, 0 - 63)</td>
1538          <td>Differentiated Services Code Point</td>
1539        </tr>
1540        <tr>
1541          <td>comment <span class="since">(Since 0.8.5)</span></td>
1542          <td>STRING</td>
1543          <td>text with max. 256 characters</td>
1544        </tr>
1545        <tr>
1546          <td>state <span class="since">(Since 0.8.5)</span></td>
1547          <td>STRING</td>
1548          <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
1549        </tr>
1550        <tr>
1551          <td>ipset <span class="since">(Since 0.9.13)</span></td>
1552          <td>STRING</td>
1553          <td>The name of an IPSet managed outside of libvirt</td>
1554        </tr>
1555        <tr>
1556          <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
1557          <td>IPSETFLAGS</td>
1558          <td>flags for the IPSet; requires ipset attribute</td>
1559        </tr>
1560       </table>
1561     <p>
1562       <br/><br/>
1563     </p>
1564
1565
1566     <h5><a id="nwfelemsRulesProtoTCP-ipv6">TCP/UDP/SCTP over IPV6</a></h5>
1567     <p>
1568       Protocol ID: <code>tcp-ipv6</code>, <code>udp-ipv6</code>, <code>sctp-ipv6</code>
1569       <br/>
1570       Note: The chain parameter is ignored for this type of traffic
1571       and should either be omitted or set to <code>root</code>.
1572     </p>
1573       <table class="top_table">
1574        <tr>
1575          <th> Attribute </th>
1576          <th> Datatype </th>
1577          <th> Semantics </th>
1578        </tr>
1579        <tr>
1580          <td>srcmacaddr</td>
1581          <td>MAC_ADDR</td>
1582          <td>MAC address of sender</td>
1583        </tr>
1584        <tr>
1585          <td>srcipaddr</td>
1586          <td>IPV6_ADDR</td>
1587          <td>Source IP address</td>
1588        </tr>
1589        <tr>
1590          <td>srcipmask</td>
1591          <td>IPV6_MASK</td>
1592          <td>Mask applied to source IP address</td>
1593        </tr>
1594        <tr>
1595          <td>dstipaddr</td>
1596          <td>IPV6_ADDR</td>
1597          <td>Destination IP address</td>
1598        </tr>
1599        <tr>
1600          <td>dstipmask</td>
1601          <td>IPV6_MASK</td>
1602          <td>Mask applied to destination IP address</td>
1603        </tr>
1604
1605        <tr>
1606          <td>srcipfrom</td>
1607          <td>IPV6_ADDR</td>
1608          <td>Start of range of source IP address</td>
1609        </tr>
1610        <tr>
1611          <td>srcipto</td>
1612          <td>IPV6_ADDR</td>
1613          <td>End of range of source IP address</td>
1614        </tr>
1615        <tr>
1616          <td>dstipfrom</td>
1617          <td>IPV6_ADDR</td>
1618          <td>Start of range of destination IP address</td>
1619        </tr>
1620        <tr>
1621          <td>dstipto</td>
1622          <td>IPV6_ADDR</td>
1623          <td>End of range of destination IP address</td>
1624        </tr>
1625
1626        <tr>
1627          <td>srcportstart</td>
1628          <td>UINT16</td>
1629          <td>Start of range of valid source ports</td>
1630        </tr>
1631        <tr>
1632          <td>srcportend</td>
1633          <td>UINT16</td>
1634          <td>End of range of valid source ports</td>
1635        </tr>
1636        <tr>
1637          <td>dstportstart</td>
1638          <td>UINT16</td>
1639          <td>Start of range of valid destination ports</td>
1640        </tr>
1641        <tr>
1642          <td>dstportend</td>
1643          <td>UINT16</td>
1644          <td>End of range of valid destination ports</td>
1645        </tr>
1646        <tr>
1647          <td>dscp</td>
1648          <td>UINT8 (0x0-0x3f, 0 - 63)</td>
1649          <td>Differentiated Services Code Point</td>
1650        </tr>
1651        <tr>
1652          <td>comment <span class="since">(Since 0.8.5)</span></td>
1653          <td>STRING</td>
1654          <td>text with max. 256 characters</td>
1655        </tr>
1656        <tr>
1657          <td>state <span class="since">(Since 0.8.5)</span></td>
1658          <td>STRING</td>
1659          <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
1660        </tr>
1661        <tr>
1662          <td>flags <span class="since">(Since 0.9.1)</span></td>
1663          <td>STRING</td>
1664          <td>TCP-only: format of mask/flags with mask and flags each being a comma separated list of SYN,ACK,URG,PSH,FIN,RST or NONE or ALL</td>
1665        </tr>
1666        <tr>
1667          <td>ipset <span class="since">(Since 0.9.13)</span></td>
1668          <td>STRING</td>
1669          <td>The name of an IPSet managed outside of libvirt</td>
1670        </tr>
1671        <tr>
1672          <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
1673          <td>IPSETFLAGS</td>
1674          <td>flags for the IPSet; requires ipset attribute</td>
1675        </tr>
1676       </table>
1677     <p>
1678       <br/><br/>
1679     </p>
1680
1681
1682     <h5><a id="nwfelemsRulesProtoICMPv6">ICMPv6</a></h5>
1683     <p>
1684       Protocol ID: <code>icmpv6</code>
1685       <br/>
1686       Note: The chain parameter is ignored for this type of traffic
1687       and should either be omitted or set to <code>root</code>.
1688     </p>
1689       <table class="top_table">
1690        <tr>
1691          <th> Attribute </th>
1692          <th> Datatype </th>
1693          <th> Semantics </th>
1694        </tr>
1695        <tr>
1696          <td>srcmacaddr</td>
1697          <td>MAC_ADDR</td>
1698          <td>MAC address of sender</td>
1699        </tr>
1700        <tr>
1701          <td>srcipaddr</td>
1702          <td>IPV6_ADDR</td>
1703          <td>Source IPv6 address</td>
1704        </tr>
1705        <tr>
1706          <td>srcipmask</td>
1707          <td>IPV6_MASK</td>
1708          <td>Mask applied to source IPv6 address</td>
1709        </tr>
1710        <tr>
1711          <td>dstipaddr</td>
1712          <td>IPV6_ADDR</td>
1713          <td>Destination IPv6 address</td>
1714        </tr>
1715        <tr>
1716          <td>dstipmask</td>
1717          <td>IPV6_MASK</td>
1718          <td>Mask applied to destination IPv6 address</td>
1719        </tr>
1720
1721        <tr>
1722          <td>srcipfrom</td>
1723          <td>IPV6_ADDR</td>
1724          <td>Start of range of source IP address</td>
1725        </tr>
1726        <tr>
1727          <td>srcipto</td>
1728          <td>IPV6_ADDR</td>
1729          <td>End of range of source IP address</td>
1730        </tr>
1731        <tr>
1732          <td>dstipfrom</td>
1733          <td>IPV6_ADDR</td>
1734          <td>Start of range of destination IP address</td>
1735        </tr>
1736        <tr>
1737          <td>dstipto</td>
1738          <td>IPV6_ADDR</td>
1739          <td>End of range of destination IP address</td>
1740        </tr>
1741
1742        <tr>
1743          <td>type</td>
1744          <td>UINT16</td>
1745          <td>ICMPv6 type</td>
1746        </tr>
1747        <tr>
1748          <td>code</td>
1749          <td>UINT16</td>
1750          <td>ICMPv6 code</td>
1751        </tr>
1752        <tr>
1753          <td>dscp</td>
1754          <td>UINT8 (0x0-0x3f, 0 - 63)</td>
1755          <td>Differentiated Services Code Point</td>
1756        </tr>
1757        <tr>
1758          <td>comment <span class="since">(Since 0.8.5)</span></td>
1759          <td>STRING</td>
1760          <td>text with max. 256 characters</td>
1761        </tr>
1762        <tr>
1763          <td>state <span class="since">(Since 0.8.5)</span></td>
1764          <td>STRING</td>
1765          <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
1766        </tr>
1767        <tr>
1768          <td>ipset <span class="since">(Since 0.9.13)</span></td>
1769          <td>STRING</td>
1770          <td>The name of an IPSet managed outside of libvirt</td>
1771        </tr>
1772        <tr>
1773          <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
1774          <td>IPSETFLAGS</td>
1775          <td>flags for the IPSet; requires ipset attribute</td>
1776        </tr>
1777       </table>
1778     <p>
1779       <br/><br/>
1780     </p>
1781
1782     <h5><a id="nwfelemsRulesProtoMiscv6">ESP, AH, UDPLITE, 'ALL' over IPv6</a></h5>
1783     <p>
1784       Protocol ID: <code>esp-ipv6</code>, <code>ah-ipv6</code>, <code>udplite-ipv6</code>, <code>all-ipv6</code>
1785       <br/>
1786       Note: The chain parameter is ignored for this type of traffic
1787       and should either be omitted or set to <code>root</code>.
1788     </p>
1789       <table class="top_table">
1790        <tr>
1791          <th> Attribute </th>
1792          <th> Datatype </th>
1793          <th> Semantics </th>
1794        </tr>
1795        <tr>
1796          <td>srcmacaddr</td>
1797          <td>MAC_ADDR</td>
1798          <td>MAC address of sender</td>
1799        </tr>
1800        <tr>
1801          <td>srcipaddr</td>
1802          <td>IPV6_ADDR</td>
1803          <td>Source IPv6 address</td>
1804        </tr>
1805        <tr>
1806          <td>srcipmask</td>
1807          <td>IPV6_MASK</td>
1808          <td>Mask applied to source IPv6 address</td>
1809        </tr>
1810        <tr>
1811          <td>dstipaddr</td>
1812          <td>IPV6_ADDR</td>
1813          <td>Destination IPv6 address</td>
1814        </tr>
1815        <tr>
1816          <td>dstipmask</td>
1817          <td>IPV6_MASK</td>
1818          <td>Mask applied to destination IPv6 address</td>
1819        </tr>
1820
1821        <tr>
1822          <td>srcipfrom</td>
1823          <td>IPV6_ADDR</td>
1824          <td>Start of range of source IP address</td>
1825        </tr>
1826        <tr>
1827          <td>srcipto</td>
1828          <td>IPV6_ADDR</td>
1829          <td>End of range of source IP address</td>
1830        </tr>
1831        <tr>
1832          <td>dstipfrom</td>
1833          <td>IPV6_ADDR</td>
1834          <td>Start of range of destination IP address</td>
1835        </tr>
1836        <tr>
1837          <td>dstipto</td>
1838          <td>IPV6_ADDR</td>
1839          <td>End of range of destination IP address</td>
1840        </tr>
1841        <tr>
1842          <td>dscp</td>
1843          <td>UINT8 (0x0-0x3f, 0 - 63)</td>
1844          <td>Differentiated Services Code Point</td>
1845        </tr>
1846        <tr>
1847          <td>comment <span class="since">(Since 0.8.5)</span></td>
1848          <td>STRING</td>
1849          <td>text with max. 256 characters</td>
1850        </tr>
1851        <tr>
1852          <td>state <span class="since">(Since 0.8.5)</span></td>
1853          <td>STRING</td>
1854          <td>comma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE</td>
1855        </tr>
1856        <tr>
1857          <td>ipset <span class="since">(Since 0.9.13)</span></td>
1858          <td>STRING</td>
1859          <td>The name of an IPSet managed outside of libvirt</td>
1860        </tr>
1861        <tr>
1862          <td>ipsetflags <span class="since">(Since 0.9.13)</span></td>
1863          <td>IPSETFLAGS</td>
1864          <td>flags for the IPSet; requires ipset attribute</td>
1865        </tr>
1866       </table>
1867     <p>
1868       <br/><br/>
1869     </p>
1870
1871     <h3><a id="nwfelemsRulesAdv">Advanced Filter Configuration Topics</a></h3>
1872     <p>
1873      The following sections discuss advanced filter configuration
1874      topics.
1875     </p>
1876
1877     <h4><a id="nwfelemsRulesAdvTracking">Connection tracking</a></h4>
1878     <p>
1879      The network filtering subsystem (on Linux) makes use of the connection
1880      tracking support of iptables. This helps in enforcing the
1881      directionality of network traffic (state match) as well as
1882      counting and limiting the number of simultaneous connections towards
1883      a VM. As an example, if a VM has TCP port 8080
1884      open as a server, clients may connect to the VM on port 8080.
1885      Connection tracking and enforcement of directionality then prevents
1886      the VM from initiating a connection from
1887      (TCP client) port 8080 to the host back to a remote host.
1888      More importantly, tracking helps to prevent
1889      remote attackers from establishing a connection back to a VM. For example,
1890      if the user inside the VM established a connection to
1891      port 80 on an attacker site, then the attacker will not be able to
1892      initiate a connection from TCP port 80 back towards the VM.
1893      By default the connection state match that enables connection tracking
1894      and then enforcement of directionality of traffic is turned on. <br/>
1895      The following shows an example XML fragment where this feature has been
1896      turned off for incoming connections to TCP port 12345.
1897     </p>
1898 <pre>
1899 [...]
1900 &lt;rule direction='in' action='accept' statematch='false'&gt;
1901   &lt;tcp dstportstart='12345'/&gt;
1902 &lt;/rule&gt;
1903 [...]
1904 </pre>
1905     <p>
1906      This now allows incoming traffic to TCP port 12345, but would also
1907      enable the initiation from (client) TCP port 12345 within the VM,
1908      which may or may not be desirable.
1909     </p>
1910
1911     <h4><a id="nwfelemsRulesAdvLimiting">Limiting Number of Connections</a></h4>
1912     <p>
1913      To limit the number of connections a VM may establish, a rule must
1914      be provided that sets a limit of connections for a given
1915      type of traffic. If for example a VM
1916      is supposed to be allowed to only ping one other IP address at a time
1917      and is supposed to have only one active incoming ssh connection at a
1918      time, the following XML fragment can be used to achieve this.
1919     </p>
1920 <pre>
1921 [...]
1922 &lt;rule action='drop' direction='in' priority='400'&gt;
1923   &lt;tcp connlimit-above='1'/&gt;
1924 &lt;/rule&gt;
1925 &lt;rule action='accept' direction='in' priority='500'&gt;
1926   &lt;tcp dstportstart='22'/&gt;
1927 &lt;/rule&gt;
1928 &lt;rule action='drop' direction='out' priority='400'&gt;
1929   &lt;icmp connlimit-above='1'/&gt;
1930 &lt;/rule&gt;
1931 &lt;rule action='accept' direction='out' priority='500'&gt;
1932   &lt;icmp/&gt;
1933 &lt;/rule&gt;
1934 &lt;rule action='accept' direction='out' priority='500'&gt;
1935   &lt;udp dstportstart='53'/&gt;
1936 &lt;/rule&gt;
1937 &lt;rule action='drop' direction='inout' priority='1000'&gt;
1938   &lt;all/&gt;
1939 &lt;/rule&gt;
1940 [...]
1941 </pre>
1942     <p>
1943      Note that the rule for the limit has to logically appear
1944      before the rule for accepting the traffic.<br/>
1945      An additional rule for letting DNS traffic to port 22
1946      go out the VM has been added to avoid ssh sessions not
1947      getting established for reasons related to DNS lookup failures
1948      by the ssh daemon. Leaving this rule out may otherwise lead to
1949      fun-filled debugging joy (symptom: ssh client seems to hang
1950      while trying to connect).
1951      <br/><br/>
1952      Lot of care must be taken with timeouts related
1953      to tracking of traffic. An ICMP ping that
1954      the user may have terminated inside the VM may have a long
1955      timeout in the host's connection tracking system and therefore
1956      not allow another ICMP ping to go through for a while. Therefore,
1957      the timeouts have to be tuned in the host's sysfs, i.e.,
1958     </p>
1959
1960 <pre>
1961 echo 3 > /proc/sys/net/netfilter/nf_conntrack_icmp_timeout
1962 </pre>
1963     <p>
1964       sets the ICMP connection tracking timeout to 3 seconds. The
1965       effect of this is that once one ping is terminated, another
1966       one can start after 3 seconds.<br/>
1967       Further, we want to point out that a client that for whatever
1968       reason has not properly closed a TCP connection may cause a
1969       connection to be held open for a longer period of time,
1970       depending to what timeout the <code>TCP established</code> state
1971       timeout has been set to on the host. Also, idle connections may time
1972       out in the connection tracking system but can be reactivated once
1973       packets are exchanged. However, a newly initiated connection may force
1974       an idle connection into TCP backoff if the number of allowed connections
1975       is set to a too low limit, the new connection is established
1976       and hits (not exceeds) the limit of allowed connections and for
1977       example a key is pressed on the old ssh session, which now has become
1978       unresponsive due to its traffic being dropped.
1979       Therefore, the limit of connections should be rather high so that
1980       fluctuations in new TCP connections don't cause odd
1981       traffic behavior in relation to idle connections.
1982     </p>
1983
1984     <h2><a id="nwfcli">Command line tools</a></h2>
1985     <p>
1986       The libvirt command line tool <code>virsh</code> has been extended
1987       with life-cycle support for network filters. All commands related
1988       to the network filtering subsystem start with the prefix
1989       <code>nwfilter</code>. The following commands are available:
1990     </p>
1991     <ul>
1992      <li>nwfilter-list : list UUIDs and names of all network filters</li>
1993      <li>nwfilter-define : define a new network filter or update an existing one</li>
1994      <li>nwfilter-undefine : delete a network filter given its name; it must not be currently in use</li>
1995      <li>nwfilter-dumpxml : display a network filter given its name</li>
1996      <li>nwfilter-edit : edit a network filter given its name</li>
1997     </ul>
1998
1999     <h2><a id="nwfexamples">Pre-existing network filters</a></h2>
2000     <p>
2001      The following is a list of example network filters that are
2002      automatically installed with libvirt.</p>
2003       <table class="top_table">
2004        <tr>
2005          <th> Name </th>
2006          <th> Description </th>
2007        </tr>
2008        <tr>
2009          <td> no-arp-spoofing </td>
2010          <td> Prevent a VM from spoofing ARP traffic; this filter
2011               only allows ARP request and reply messages and enforces
2012               that those packets contain the MAC and IP addresses
2013               of the VM.</td>
2014       </tr>
2015        <tr>
2016          <td> allow-dhcp </td>
2017          <td> Allow a VM to request an IP address via DHCP (from any
2018               DHCP server)</td>
2019       </tr>
2020        <tr>
2021          <td> allow-dhcp-server </td>
2022          <td> Allow a VM to request an IP address from a specified
2023               DHCP server. The dotted decimal IP address of the DHCP
2024               server must be provided in a reference to this filter.
2025               The name of the variable must be <i>DHCPSERVER</i>.</td>
2026       </tr>
2027        <tr>
2028          <td> no-ip-spoofing </td>
2029          <td> Prevent a VM from sending of IP packets with
2030               a source IP address different from the one
2031               in the packet. </td>
2032       </tr>
2033        <tr>
2034          <td> no-ip-multicast </td>
2035          <td> Prevent a VM from sending IP multicast packets. </td>
2036       </tr>
2037        <tr>
2038          <td> clean-traffic </td>
2039          <td> Prevent MAC, IP and ARP spoofing. This filter references
2040               several other filters as building blocks. </td>
2041       </tr>
2042       </table>
2043     <p>
2044      Note that most of the above filters are only building blocks and
2045      require a combination with other filters to provide useful network
2046      traffic filtering.
2047      The most useful one in the above list is the <i>clean-traffic</i>
2048      filter. This filter itself can for example be combined with the
2049      <i>no-ip-multicast</i>
2050      filter to prevent virtual machines from sending IP multicast traffic
2051      on top of the prevention of packet spoofing.
2052     </p>
2053
2054     <h2><a id="nwfwrite">Writing your own filters</a></h2>
2055
2056     <p>
2057      Since libvirt only provides a couple of example networking filters, you
2058      may consider writing your own. When planning on doing so
2059      there are a couple of things
2060      you may need to know regarding the network filtering subsystem and how
2061      it works internally. Certainly you also have to know and understand
2062      the protocols very well that you want to be filtering on so that
2063      no further traffic than what you want can pass and that in fact the
2064      traffic you want to allow does pass.
2065      <br/><br/>
2066      The network filtering subsystem is currently only available on
2067      Linux hosts and only works for QEMU and KVM type of virtual machines.
2068      On Linux
2069      it builds upon the support for <code>ebtables</code>, <code>iptables
2070      </code> and <code>ip6tables</code> and makes use of their features.
2071      From the above list of supported protocols the following ones are
2072      implemented using <code>ebtables</code>:
2073     </p>
2074     <ul>
2075      <li>mac</li>
2076      <li>stp (spanning tree protocol)</li>
2077      <li>vlan (802.1Q)</li>
2078      <li>arp, rarp</li>
2079      <li>ipv4</li>
2080      <li>ipv6</li>
2081     </ul>
2082
2083     <p>
2084     All other protocols over IPv4 are supported using iptables, those over
2085     IPv6 are implemented using ip6tables.
2086     <br/><br/>
2087     On a Linux host, all traffic filtering instantiated by libvirt's network
2088     filter subsystem first passes through the filtering support implemented
2089     by ebtables and only then through iptables or ip6tables filters. If
2090     a filter tree has rules with the protocols <code>mac</code>,
2091     <code>stp</code>, <code>vlan</code>
2092     <code>arp</code>, <code>rarp</code>, <code>ipv4</code>,
2093     or <code>ipv6</code> ebtables rules will automatically be instantiated.
2094     <br/>
2095     The role of the <code>chain</code> attribute in the network filter
2096     XML is that internally a new user-defined ebtables table is created
2097     that then for example receives all <code>arp</code> traffic coming
2098     from or going to a virtual machine if the chain <code>arp</code>
2099     has been specified. Further, a rule is generated in an interface's
2100     <code>root</code> chain that directs all ipv4 traffic into the
2101     user-defined chain. Therefore, all ARP traffic rules should then be
2102     placed into filters specifying this chain. This type of branching
2103     into user-defined tables is only supported with filtering on the ebtables
2104     layer.
2105     <br/>
2106     <span class="since">Since 0.9.8</span> multiple chains for the same
2107     protocol can be created. For this the name of the chain must have
2108     a prefix of one of the previously enumerated protocols. To create an
2109     additional chain for handling of ARP traffic, a chain with name
2110     <code>arp-test</code> can be specified.
2111     <br/>
2112     As an example, it is
2113     possible to filter on UDP traffic by source and destination ports using
2114     the <code>ip</code> protocol filter and specifying attributes for the
2115     protocol, source and destination IP addresses and ports of UDP packets
2116     that are to be accepted. This allows
2117     early filtering of UDP traffic with ebtables. However, once an IP or IPv6
2118     packet, such as a UDP packet,
2119     has passed the ebtables layer and there is at least one rule in a filter
2120     tree that instantiates iptables or ip6tables rules, a rule to let
2121     the UDP packet pass will also be necessary to be provided for those
2122     filtering layers. This can be
2123     achieved with a rule containing an appropriate <code>udp</code> or
2124     <code>udp-ipv6</code> traffic filtering node.
2125     </p>
2126
2127     <h3><a id="nwfwriteexample">Example custom filter</a></h3>
2128     <p>
2129      As an example we want to now build a filter that fulfills the following
2130      list of requirements:
2131     </p>
2132     <ul>
2133      <li>prevents a VM's interface from MAC, IP and ARP spoofing</li>
2134      <li>opens only TCP ports 22 and 80 of a VM's interface</li>
2135      <li>allows the VM to send ping traffic from an interface
2136         but not let the VM be pinged on the interface</li>
2137      <li>allows the VM to do DNS lookups (UDP towards port 53)</li>
2138     </ul>
2139     <p>
2140      The requirement to prevent spoofing is fulfilled by the existing
2141      <code>clean-traffic</code> network filter, thus we will reference this
2142      filter from our custom filter.
2143      <br/>
2144      To enable traffic for TCP ports 22 and 80 we will add 2 rules to
2145      enable this type of traffic. To allow the VM to send ping traffic
2146      we will add a rule for ICMP traffic. For simplicity reasons
2147      we allow general ICMP traffic to be initiated from the VM, not
2148      just ICMP echo request and response messages. To then
2149      disallow all other traffic to reach or be initiated by the
2150      VM we will then need to add a rule that drops all other traffic.
2151      Assuming our VM is called <i>test</i> and
2152      the interface we want to associate our filter with is called <i>eth0</i>,
2153      we name our filter <i>test-eth0</i>.
2154      The result of these considerations is the following network filter XML:
2155     </p>
2156 <pre>
2157 &lt;filter name='test-eth0'&gt;
2158   &lt;!-- reference the clean traffic filter to prevent
2159        MAC, IP and ARP spoofing. By not providing
2160        and IP address parameter, libvirt will detect the
2161        IP address the VM is using. --&gt;
2162   &lt;filterref filter='clean-traffic'/&gt;
2163
2164   &lt;!-- enable TCP ports 22 (ssh) and 80 (http) to be reachable --&gt;
2165   &lt;rule action='accept' direction='in'&gt;
2166     &lt;tcp dstportstart='22'/&gt;
2167   &lt;/rule&gt;
2168
2169   &lt;rule action='accept' direction='in'&gt;
2170     &lt;tcp dstportstart='80'/&gt;
2171   &lt;/rule&gt;
2172
2173   &lt;!-- enable general ICMP traffic to be initiated by the VM;
2174        this includes ping traffic --&gt;
2175   &lt;rule action='accept' direction='out'&gt;
2176     &lt;icmp/&gt;
2177   &lt;/rule&gt;
2178
2179   &lt;!-- enable outgoing DNS lookups using UDP --&gt;
2180   &lt;rule action='accept' direction='out'&gt;
2181     &lt;udp dstportstart='53'/&gt;
2182   &lt;/rule&gt;
2183
2184   &lt;!-- drop all other traffic --&gt;
2185   &lt;rule action='drop' direction='inout'&gt;
2186     &lt;all/&gt;
2187   &lt;/rule&gt;
2188
2189 &lt;/filter&gt;
2190 </pre>
2191     <p>
2192      Note that none of the rules in the above XML contain the
2193      IP address of the VM as either source or destination address, yet
2194      the filtering of the traffic works correctly. The reason is that
2195      the evaluation  of the rules internally happens on a
2196      per-interface basis and the rules are evaluated based on the knowledge
2197      about which (tap) interface has sent or will receive the packet rather
2198      than what their source or destination IP address may be.
2199      <br/><br/>
2200      An XML fragment for a possible network interface description inside
2201      the domain XML of the <code>test</code> VM could then look like this:
2202     </p>
2203 <pre>
2204 [...]
2205 &lt;interface type='bridge'&gt;
2206   &lt;source bridge='mybridge'/&gt;
2207   &lt;filterref filter='test-eth0'/&gt;
2208 &lt;/interface&gt;
2209 [...]
2210 </pre>
2211
2212     <p>
2213      To more strictly control the ICMP traffic and enforce that only
2214      ICMP echo requests can be sent from the VM
2215      and only ICMP echo responses be received by the VM, the above
2216      <code>ICMP</code> rule can be replaced with the following two rules:
2217     </p>
2218 <pre>
2219 &lt;!-- enable outgoing ICMP echo requests--&gt;
2220 &lt;rule action='accept' direction='out'&gt;
2221   &lt;icmp type='8'/&gt;
2222 &lt;/rule&gt;
2223
2224 &lt;!-- enable incoming ICMP echo replies--&gt;
2225 &lt;rule action='accept' direction='in'&gt;
2226   &lt;icmp type='0'/&gt;
2227 &lt;/rule&gt;
2228 </pre>
2229
2230     <h3><a id="nwfwriteexample2nd">Second example custom filter</a></h3>
2231     <p>
2232      In this example we now want to build a similar filter as in the
2233      example above, but extend the list of requirements with an
2234      ftp server located inside the VM. Further, we will be using features
2235      that have been added in <span class="since">version 0.8.5</span>.
2236      The requirements for this filter are:
2237     </p>
2238     <ul>
2239      <li>prevents a VM's interface from MAC, IP and ARP spoofing</li>
2240      <li>opens only TCP ports 22 and 80 of a VM's interface</li>
2241      <li>allows the VM to send ping traffic from an interface
2242         but not let the VM be pinged on the interface</li>
2243      <li>allows the VM to do DNS lookups (UDP towards port 53)</li>
2244      <li>enable an ftp server (in active mode) to be run inside the VM</li>
2245     </ul>
2246     <p>
2247      The additional requirement of allowing an ftp server to be run inside
2248      the VM maps into the requirement of allowing port 21 to be reachable
2249      for ftp control traffic as well as enabling the VM to establish an
2250      outgoing tcp connection originating from the VM's TCP port 20 back to
2251      the ftp client (ftp active mode). There are several ways of how this
2252      filter can be written and we present 2 solutions.
2253      <br/><br/>
2254      The 1st solution makes use of the <code>state</code> attribute of
2255      the TCP protocol that gives us a hook into the connection tracking
2256      framework of the Linux host. For the VM-initiated ftp data connection
2257      (ftp active mode) we use the <code>RELATED</code> state that allows
2258      us to detect that the VM-initiated ftp data connection is a consequence of
2259      ( or 'has a relationship with' ) an existing ftp control connection,
2260      thus we want to allow it to let packets
2261      pass the firewall. The <code>RELATED</code> state, however, is only
2262      valid for the very first packet of the outgoing TCP connection for the
2263      ftp data path. Afterwards, the state to compare against is
2264      <code>ESTABLISHED</code>, which then applies equally
2265      to the incoming and outgoing direction. All this is related to the ftp
2266      data traffic originating from TCP port 20 of the VM. This then leads to
2267      the following solution
2268      <span class="since">(since 0.8.5 (QEMU, KVM))</span>:
2269     </p>
2270 <pre>
2271 &lt;filter name='test-eth0'&gt;
2272   &lt;!-- reference the clean traffic filter to prevent
2273        MAC, IP and ARP spoofing. By not providing
2274        and IP address parameter, libvirt will detect the
2275        IP address the VM is using. --&gt;
2276   &lt;filterref filter='clean-traffic'/&gt;
2277
2278   &lt;!-- enable TCP port 21 (ftp-control) to be reachable --&gt;
2279   &lt;rule action='accept' direction='in'&gt;
2280     &lt;tcp dstportstart='21'/&gt;
2281   &lt;/rule&gt;
2282
2283   &lt;!-- enable TCP port 20 for VM-initiated ftp data connection
2284        related to an existing ftp control connection --&gt;
2285   &lt;rule action='accept' direction='out'&gt;
2286     &lt;tcp srcportstart='20' state='RELATED,ESTABLISHED'/&gt;
2287   &lt;/rule&gt;
2288
2289   &lt;!-- accept all packets from client on the ftp data connection --&gt;
2290   &lt;rule action='accept' direction='in'&gt;
2291     &lt;tcp dstportstart='20' state='ESTABLISHED'/&gt;
2292   &lt;/rule&gt;
2293
2294   &lt;!-- enable TCP ports 22 (ssh) and 80 (http) to be reachable --&gt;
2295   &lt;rule action='accept' direction='in'&gt;
2296     &lt;tcp dstportstart='22'/&gt;
2297   &lt;/rule&gt;
2298
2299   &lt;rule action='accept' direction='in'&gt;
2300     &lt;tcp dstportstart='80'/&gt;
2301   &lt;/rule&gt;
2302
2303   &lt;!-- enable general ICMP traffic to be initiated by the VM;
2304        this includes ping traffic --&gt;
2305   &lt;rule action='accept' direction='out'&gt;
2306     &lt;icmp/&gt;
2307   &lt;/rule&gt;
2308
2309   &lt;!-- enable outgoing DNS lookups using UDP --&gt;
2310   &lt;rule action='accept' direction='out'&gt;
2311     &lt;udp dstportstart='53'/&gt;
2312   &lt;/rule&gt;
2313
2314   &lt;!-- drop all other traffic --&gt;
2315   &lt;rule action='drop' direction='inout'&gt;
2316     &lt;all/&gt;
2317   &lt;/rule&gt;
2318
2319 &lt;/filter&gt;
2320 </pre>
2321     <p>
2322      Before trying out a filter using the <code>RELATED</code> state,
2323      you have to make sure that the appropriate connection tracking module
2324      has been loaded into the host's kernel. Depending on the version of the
2325      kernel, you must run either one of the following two commands before
2326      the ftp connection with the VM is established.
2327     </p>
2328 <pre>
2329 modprobe nf_conntrack_ftp   # where available  or
2330
2331 modprobe ip_conntrack_ftp   # if above is not available
2332 </pre>
2333     <p>
2334      If other protocols than ftp are to be used in conjunction with the
2335      <code>RELATED</code> state, their corresponding module must be loaded.
2336      Modules exist at least for the protocols ftp, tftp, irc, sip,
2337      sctp, and amanda.
2338     </p>
2339     <p>
2340      The 2nd solution makes uses the state flags of connections more
2341      than the previous solution did.
2342      In this solution we take advantage of the fact that the
2343      <code>NEW</code> state of a connection is valid when the very
2344      first packet of a traffic flow is seen. Subsequently, if the very first
2345      packet of a flow is accepted, the flow becomes a connection and enters
2346      the <code>ESTABLISHED</code> state. This allows us to write a general
2347      rule for allowing packets of <code>ESTABLISHED</code> connections to
2348      reach the VM or be sent by the VM.
2349      We write specific rules for the very first packets identified by the
2350      <code>NEW</code> state and for which ports they are acceptable. All
2351      packets for ports that are not explicitly accepted will be dropped and
2352      therefore the connection will not go into the <code>ESTABLISHED</code>
2353      state and any subsequent packets be dropped.
2354     </p>
2355
2356 <pre>
2357 &lt;filter name='test-eth0'&gt;
2358   &lt;!-- reference the clean traffic filter to prevent
2359        MAC, IP and ARP spoofing. By not providing
2360        and IP address parameter, libvirt will detect the
2361        IP address the VM is using. --&gt;
2362   &lt;filterref filter='clean-traffic'/&gt;
2363
2364   &lt;!-- let the packets of all previously accepted connections reach the VM --&gt;
2365   &lt;rule action='accept' direction='in'&gt;
2366     &lt;all state='ESTABLISHED'/&gt;
2367   &lt;/rule&gt;
2368
2369   &lt;!-- let the packets of all previously accepted and related connections be sent from the VM --&gt;
2370   &lt;rule action='accept' direction='out'&gt;
2371     &lt;all state='ESTABLISHED,RELATED'/&gt;
2372   &lt;/rule&gt;
2373
2374   &lt;!-- enable traffic towards port 21 (ftp), 22 (ssh) and 80 (http) --&gt;
2375   &lt;rule action='accept' direction='in'&gt;
2376     &lt;tcp dstportstart='21' dstportend='22' state='NEW'/&gt;
2377   &lt;/rule&gt;
2378
2379   &lt;rule action='accept' direction='in'&gt;
2380     &lt;tcp dstportstart='80' state='NEW'/&gt;
2381   &lt;/rule&gt;
2382
2383   &lt;!-- enable general ICMP traffic to be initiated by the VM;
2384        this includes ping traffic --&gt;
2385   &lt;rule action='accept' direction='out'&gt;
2386     &lt;icmp state='NEW'/&gt;
2387   &lt;/rule&gt;
2388
2389   &lt;!-- enable outgoing DNS lookups using UDP --&gt;
2390   &lt;rule action='accept' direction='out'&gt;
2391     &lt;udp dstportstart='53' state='NEW'/&gt;
2392   &lt;/rule&gt;
2393
2394   &lt;!-- drop all other traffic --&gt;
2395   &lt;rule action='drop' direction='inout'&gt;
2396     &lt;all/&gt;
2397   &lt;/rule&gt;
2398
2399 &lt;/filter&gt;
2400
2401 </pre>
2402
2403     <h2><a id="nwflimits">Limitations</a></h2>
2404     <p>
2405      The following sections list (current) limitations of the network
2406      filtering subsystem.
2407     </p>
2408
2409     <h3><a id="nwflimitsmigr">VM Migration</a></h3>
2410      <p>
2411       VM migration is only supported if the whole filter tree
2412       that is referenced by a virtual machine's top level filter
2413       is also available on the target host. The network filter
2414       <i>clean-traffic</i>
2415       for example should be available on all libvirt installations
2416       of version 0.8.1 or later and thus enable migration of VMs that
2417       for example reference this filter. All other
2418       custom filters must be migrated using higher layer software. It is
2419       outside the scope of libvirt to ensure that referenced filters
2420       on the source system are equivalent to those on the target system
2421       and vice versa.
2422       <br/><br/>
2423       Migration must occur between libvirt installations of version
2424       0.8.1 or later in order not to lose the network traffic filters
2425       associated with an interface.
2426      </p>
2427     <h3><a id="nwflimitsvlan">VLAN filtering on Linux</a></h3>
2428      <p>
2429       VLAN (802.1Q) packets, if sent by a virtual machine, cannot be filtered
2430       with rules for protocol IDs <code>arp</code>, <code>rarp</code>,
2431       <code>ipv4</code> and <code>ipv6</code> but only
2432       with protocol IDs <code>mac</code> and <code>vlan</code>. Therefore,
2433       the example filter <code>clean-traffic</code> will not work as expected.
2434      </p>
2435   </body>
2436 </html>