Display detected IP addresses in the domain XML using the
IP_LEASE variable name. This variable name now becomes
a reserved variable name that can be read only but not set
by the user.

The format of the value is: <ip addresss>,<lease timeout in seconds>

An example of a displayed XML may then be:

    <interface type='bridge'>
      <mac address='52:54:00:68:e3:90'/>
      <source bridge='virbr0'/>
      <target dev='vnet1'/>
      <model type='virtio'/>
      <filterref filter='clean-traffic'>
        <parameter name='CTRL_IP_LEARNING' value='dhcp'/>
        <parameter name='IP_LEASE' value='192.168.122.210,100'/>
      </filterref>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </interface>


---
 docs/formatnwfilter.html.in            |   27 ++++++++++++++++
 src/conf/domain_conf.c                 |   16 +++++++--
 src/conf/domain_nwfilter.c             |   11 ++++++
 src/conf/domain_nwfilter.h             |   12 +++++++
 src/conf/nwfilter_conf.c               |    3 +
 src/conf/nwfilter_ipaddrmap.c          |   29 ++++++++++++++++++
 src/conf/nwfilter_ipaddrmap.h          |    5 +++
 src/conf/nwfilter_params.c             |   45 ++++++++++++++++++++++++++--
 src/conf/nwfilter_params.h             |    9 ++++-
 src/libvirt_private.syms               |    3 +
 src/nwfilter/nwfilter_dhcpsnoop.c      |   53 +++++++++++++++++++++++++++++++++
 src/nwfilter/nwfilter_dhcpsnoop.h      |    4 ++
 src/nwfilter/nwfilter_driver.c         |   10 ++++++
 src/nwfilter/nwfilter_gentech_driver.c |   24 ++++++++++++++
 src/nwfilter/nwfilter_gentech_driver.h |    6 +++
 src/nwfilter/nwfilter_learnipaddr.c    |   14 ++++++++
 src/nwfilter/nwfilter_learnipaddr.h    |    2 +
 17 files changed, 264 insertions(+), 9 deletions(-)

Index: libvirt-acl/src/conf/nwfilter_params.h
===================================================================
--- libvirt-acl.orig/src/conf/nwfilter_params.h
+++ libvirt-acl/src/conf/nwfilter_params.h
@@ -72,7 +72,10 @@ struct _virNWFilterHashTable {
 virNWFilterHashTablePtr virNWFilterParseParamAttributes(xmlNodePtr cur);
 int virNWFilterFormatParamAttributes(virBufferPtr buf,
                                      virNWFilterHashTablePtr table,
-                                     const char *filterref);
+                                     const char *filterref,
+                                     const unsigned char *vmuuid,
+                                     const unsigned char *mac,
+                                     const char *ifname);
 
 virNWFilterHashTablePtr virNWFilterHashTableCreate(int n);
 void virNWFilterHashTableFree(virNWFilterHashTablePtr table);
@@ -89,12 +92,14 @@ int virNWFilterHashTablePutAll(virNWFilt
   "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_"
 
 # define VALID_VARVALUE \
-  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_.:"
+  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_.:,"
 
 # define NWFILTER_VARNAME_IP "IP"
 # define NWFILTER_VARNAME_MAC "MAC"
 # define NWFILTER_VARNAME_CTRL_IP_LEARNING "CTRL_IP_LEARNING"
 # define NWFILTER_VARNAME_DHCPSERVER "DHCPSERVER"
+# define NWFILTER_VARNAME_IP_LEASE "IP_LEASE"
+# define NWFILTER_VARNAME_IPV6_LEASE "IPV6_LEASE" /* future */
 
 enum virNWFilterVarAccessType {
     VIR_NWFILTER_VAR_ACCESS_ELEMENT = 0,
Index: libvirt-acl/src/conf/domain_conf.c
===================================================================
--- libvirt-acl.orig/src/conf/domain_conf.c
+++ libvirt-acl/src/conf/domain_conf.c
@@ -43,6 +43,7 @@
 #include "buf.h"
 #include "c-ctype.h"
 #include "logging.h"
+#include "nwfilter_params.h"
 #include "nwfilter_conf.h"
 #include "ignore-value.h"
 #include "storage_file.h"
@@ -11258,7 +11259,8 @@ error:
 static int
 virDomainNetDefFormat(virBufferPtr buf,
                       virDomainNetDefPtr def,
-                      unsigned int flags)
+                      unsigned int flags,
+                      const unsigned char *vmuuid)
 {
     const char *type = virDomainNetTypeToString(def->type);
 
@@ -11399,9 +11401,15 @@ virDomainNetDefFormat(virBufferPtr buf,
         }
     }
     if (def->filter) {
+        const char *ifname = NULL;
+
+        if (!(flags & VIR_DOMAIN_XML_INACTIVE))
+            ifname = def->ifname;
+
         virBufferAdjustIndent(buf, 6);
         if (virNWFilterFormatParamAttributes(buf, def->filterparams,
-                                             def->filter) < 0)
+                                             def->filter, vmuuid, def->mac,
+                                             ifname) < 0)
             return -1;
         virBufferAdjustIndent(buf, -6);
     }
@@ -12684,7 +12692,7 @@ virDomainDefFormatInternal(virDomainDefP
 
 
     for (n = 0 ; n < def->nnets ; n++)
-        if (virDomainNetDefFormat(buf, def->nets[n], flags) < 0)
+        if (virDomainNetDefFormat(buf, def->nets[n], flags, def->uuid) < 0)
             goto cleanup;
 
     for (n = 0 ; n < def->nsmartcards ; n++)
@@ -14937,7 +14945,7 @@ virDomainDeviceDefCopy(virCapsPtr caps,
         rc = virDomainFSDefFormat(&buf, src->data.fs, flags);
         break;
     case VIR_DOMAIN_DEVICE_NET:
-        rc = virDomainNetDefFormat(&buf, src->data.net, flags);
+        rc = virDomainNetDefFormat(&buf, src->data.net, flags, def->uuid);
         break;
     case VIR_DOMAIN_DEVICE_INPUT:
         rc = virDomainInputDefFormat(&buf, src->data.input, flags);
Index: libvirt-acl/src/conf/nwfilter_conf.c
===================================================================
--- libvirt-acl.orig/src/conf/nwfilter_conf.c
+++ libvirt-acl/src/conf/nwfilter_conf.c
@@ -3406,7 +3406,8 @@ virNWFilterIncludeDefFormat(virNWFilterI
 
     virBufferAdjustIndent(&buf, 2);
     if (virNWFilterFormatParamAttributes(&buf, inc->params,
-                                         inc->filterref) < 0) {
+                                         inc->filterref,
+                                         NULL, NULL, NULL) < 0) {
         virBufferFreeAndReset(&buf);
         return NULL;
     }
Index: libvirt-acl/src/libvirt_private.syms
===================================================================
--- libvirt-acl.orig/src/libvirt_private.syms
+++ libvirt-acl/src/libvirt_private.syms
@@ -545,6 +545,7 @@ virDomainLockLeaseDetach;
 
 
 # domain_nwfilter.h
+virDomainConfNWFilterFormatLeases;
 virDomainConfNWFilterInstantiate;
 virDomainConfNWFilterRegister;
 virDomainConfNWFilterTeardown;
@@ -856,6 +857,7 @@ virNWFilterUnlockFilterUpdates;
 # nwfilter_ipaddrmap
 virNWFilterIPAddrMapAddIPAddr;
 virNWFilterIPAddrMapDelIPAddr;
+virNWFilterIPAddrMapFormatIPAddrs;
 virNWFilterIPAddrMapGetIPAddr;
 virNWFilterIPAddrMapInit;
 virNWFilterIPAddrMapShutdown;
@@ -883,6 +885,7 @@ virNWFilterVarValueFree;
 virNWFilterVarValueGetCardinality;
 virNWFilterVarValueGetNthValue;
 virNWFilterVarValueGetSimple;
+virNWFilterFormatParamAttributes;
 
 
 # pci.h
Index: libvirt-acl/src/conf/nwfilter_params.c
===================================================================
--- libvirt-acl.orig/src/conf/nwfilter_params.c
+++ libvirt-acl/src/conf/nwfilter_params.c
@@ -30,10 +30,17 @@
 #include "datatypes.h"
 #include "nwfilter_params.h"
 #include "domain_conf.h"
+#include "domain_nwfilter.h"
+#include "nwfilter_ipaddrmap.h"
 
 
 #define VIR_FROM_THIS VIR_FROM_NWFILTER
 
+static const char *virNWFilterReservedVarnames[] = {
+    NWFILTER_VARNAME_IP_LEASE,
+    NWFILTER_VARNAME_IPV6_LEASE,
+};
+
 static bool isValidVarValue(const char *value);
 static void virNWFilterVarAccessSetIntIterId(virNWFilterVarAccessPtr,
                                              unsigned int);
@@ -747,7 +754,6 @@ err_exit:
     return -1;
 }
 
-
 static bool
 isValidVarName(const char *var)
 {
@@ -767,6 +773,19 @@ virNWFilterParseVarValue(const char *val
     return virNWFilterVarValueCreateSimpleCopyValue(val);
 }
 
+static void
+virNWFilterDelReservedVarnames(virNWFilterHashTablePtr ht)
+{
+    unsigned int i;
+    virNWFilterVarValuePtr val;
+
+    for (i = 0; i < ARRAY_CARDINALITY(virNWFilterReservedVarnames); i++) {
+        val = virNWFilterHashTableRemoveEntry(ht,
+                                              virNWFilterReservedVarnames[i]);
+        virNWFilterVarValueFree(val);
+    }
+}
+
 virNWFilterHashTablePtr
 virNWFilterParseParamAttributes(xmlNodePtr cur)
 {
@@ -817,6 +836,15 @@ skip_entry:
         }
         cur = cur->next;
     }
+
+    /*
+     * read-only variables that may be usable in an incoming
+     * migration could be wired up here.
+     */
+
+    /* remove all reserved varnames from the table */
+    virNWFilterDelReservedVarnames(table);
+
     return table;
 
 err_exit:
@@ -838,7 +866,10 @@ virNWFilterFormatParameterNameSorter(con
 int
 virNWFilterFormatParamAttributes(virBufferPtr buf,
                                  virNWFilterHashTablePtr table,
-                                 const char *filterref)
+                                 const char *filterref,
+                                 const unsigned char *vmuuid,
+                                 const unsigned char *mac,
+                                 const char *ifname)
 {
     virHashKeyValuePairPtr items;
     int i, j, card, numKeys;
@@ -872,6 +903,16 @@ virNWFilterFormatParamAttributes(virBuff
                                   virNWFilterVarValueGetNthValue(value, j));
 
         }
+        if (ifname) {
+            virBufferAdjustIndent(buf, 2);
+            /* also display the IP addresses being used */
+            virDomainConfNWFilterFormatLeases(buf,
+                                              table,
+                                              ifname,
+                                              vmuuid,
+                                              mac);
+            virBufferAdjustIndent(buf, -2);
+        }
         virBufferAddLit(buf, "</filterref>\n");
     } else {
         virBufferAddLit(buf, "/>\n");
Index: libvirt-acl/src/nwfilter/nwfilter_dhcpsnoop.c
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_dhcpsnoop.c
+++ libvirt-acl/src/nwfilter/nwfilter_dhcpsnoop.c
@@ -1990,6 +1990,52 @@ virNWFilterSnoopLeaseFileLoad(void)
 }
 
 /*
+ * Format the detected IP addresses for display in the domain's
+ * XML inside a <parameter name=... value=.../> XML node.
+ */
+void
+virNWFilterSnoopFormatLeases(virBufferPtr buf,
+                             const unsigned char *vmuuid,
+                             const unsigned char *macaddr)
+{
+    char ifkey[VIR_IFKEY_LEN];
+    virNWFilterSnoopReqPtr req;
+    virNWFilterSnoopIPLeasePtr ipl;
+    char *ipbuf;
+
+    virNWFilterSnoopIFKeyFMT(ifkey, vmuuid, macaddr);
+
+    req = virNWFilterSnoopReqGetByIFKey(ifkey);
+    if (req) {
+        time_t now = time(0);
+
+        /* protect req->start */
+        virNWFilterSnoopReqLock(req);
+
+        for (ipl = req->start; ipl; ipl = ipl->next) {
+            if (ipl->timeout <= now)
+                continue;
+
+            ipbuf = virSocketAddrFormat(&ipl->ipAddress);
+            if (!ipbuf)
+                continue;
+
+            virBufferAsprintf(buf,
+                              "<parameter name='"
+                               NWFILTER_VARNAME_IP_LEASE
+                               "' value='%s,%u'/>\n",
+                              ipbuf,
+                              (unsigned int)(ipl->timeout - now));
+            VIR_FREE(ipbuf);
+        }
+
+        virNWFilterSnoopReqUnlock(req);
+
+        virNWFilterSnoopReqPut(req);
+    }
+}
+
+/*
  * Wait until all threads have ended.
  */
 static void
@@ -2175,6 +2221,13 @@ virNWFilterDHCPSnoopShutdown(void)
 
 #else /* HAVE_LIBPCAP */
 
+void
+virNWFilterSnoopFormatLeases(virBufferPtr buf ATTRIBUTE_UNUSED,
+                             const unsigned char *vmuuid ATTRIBUTE_UNUSED,
+                             const unsigned char *macaddr ATTRIBUTE_UNUSED)
+{
+}
+
 int
 virNWFilterDHCPSnoopInit(void)
 {
Index: libvirt-acl/src/nwfilter/nwfilter_dhcpsnoop.h
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_dhcpsnoop.h
+++ libvirt-acl/src/nwfilter/nwfilter_dhcpsnoop.h
@@ -36,4 +36,8 @@ int virNWFilterDHCPSnoopReq(virNWFilterT
                             virNWFilterHashTablePtr filterparams,
                             virNWFilterDriverStatePtr driver);
 void virNWFilterDHCPSnoopEnd(const char *ifname);
+void virNWFilterSnoopFormatLeases(virBufferPtr buf,
+                                  const unsigned char *vmuuid,
+                                  const unsigned char *macaddr);
+
 #endif /* __NWFILTER_DHCPSNOOP_H */
Index: libvirt-acl/src/conf/domain_nwfilter.c
===================================================================
--- libvirt-acl.orig/src/conf/domain_nwfilter.c
+++ libvirt-acl/src/conf/domain_nwfilter.c
@@ -60,3 +60,14 @@ virDomainConfVMNWFilterTeardown(virDomai
             virDomainConfNWFilterTeardown(vm->def->nets[i]);
     }
 }
+
+void
+virDomainConfNWFilterFormatLeases(virBufferPtr buf,
+                                  virNWFilterHashTablePtr table,
+                                  const char *ifname,
+                                  const unsigned char *vmuuid,
+                                  const unsigned char *mac)
+{
+    if (nwfilterDriver != NULL)
+        nwfilterDriver->formatLeases(buf, table, ifname, vmuuid, mac);
+}
Index: libvirt-acl/src/conf/domain_nwfilter.h
===================================================================
--- libvirt-acl.orig/src/conf/domain_nwfilter.h
+++ libvirt-acl/src/conf/domain_nwfilter.h
@@ -28,9 +28,16 @@ typedef int (*virDomainConfInstantiateNW
                                                 virDomainNetDefPtr net);
 typedef void (*virDomainConfTeardownNWFilter)(virDomainNetDefPtr net);
 
+typedef void (*virDomainConfFormatLeases)(virBufferPtr buf,
+                                          virNWFilterHashTablePtr table,
+                                          const char *ifname,
+                                          const unsigned char *vmuuid,
+                                          const unsigned char *mac);
+
 typedef struct {
     virDomainConfInstantiateNWFilter instantiateFilter;
     virDomainConfTeardownNWFilter    teardownFilter;
+    virDomainConfFormatLeases        formatLeases;
 } virDomainConfNWFilterDriver;
 typedef virDomainConfNWFilterDriver *virDomainConfNWFilterDriverPtr;
 
@@ -41,5 +48,10 @@ int virDomainConfNWFilterInstantiate(vir
                                      virDomainNetDefPtr net);
 void virDomainConfNWFilterTeardown(virDomainNetDefPtr net);
 void virDomainConfVMNWFilterTeardown(virDomainObjPtr vm);
+void virDomainConfNWFilterFormatLeases(virBufferPtr buf,
+                                       virNWFilterHashTablePtr table,
+                                       const char *ifname,
+                                       const unsigned char *vmuuid,
+                                       const unsigned char *mac);
 
 #endif /* DOMAIN_NWFILTER_H */
Index: libvirt-acl/src/nwfilter/nwfilter_gentech_driver.c
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_gentech_driver.c
+++ libvirt-acl/src/nwfilter/nwfilter_gentech_driver.c
@@ -1209,3 +1209,27 @@ virNWFilterDomainFWUpdateCB(void *payloa
 
     virDomainObjUnlock(obj);
 }
+
+void
+virNWFilterFormatLeases(virBufferPtr buf,
+                        virNWFilterHashTablePtr vars,
+                        const char *ifname,
+                        const unsigned char *vmuuid,
+                        const unsigned char *mac)
+{
+    virNWFilterVarValuePtr lv;
+    const char *learning = NULL;
+
+    if (!vars)
+        return;
+
+    lv = virHashLookup(vars->hashTable, NWFILTER_VARNAME_CTRL_IP_LEARNING);
+    if (lv)
+        learning = virNWFilterVarValueGetNthValue(lv, 0);
+
+    if (!learning || STRCASEEQ(learning, "any")) {
+        virNWFilterLearnFormatLeases(buf, ifname);
+    } else if (STRCASEEQ(learning, "dhcp")) {
+        virNWFilterSnoopFormatLeases(buf, vmuuid, mac);
+    }
+}
Index: libvirt-acl/src/nwfilter/nwfilter_gentech_driver.h
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_gentech_driver.h
+++ libvirt-acl/src/nwfilter/nwfilter_gentech_driver.h
@@ -64,4 +64,10 @@ void virNWFilterDomainFWUpdateCB(void *p
                                  const void *name,
                                  void *data);
 
+void virNWFilterFormatLeases(virBufferPtr buf,
+                             virNWFilterHashTablePtr vars,
+                             const char *ifname,
+                             const unsigned char *vmmuid,
+                             const unsigned char *mac);
+
 #endif
Index: libvirt-acl/src/nwfilter/nwfilter_driver.c
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_driver.c
+++ libvirt-acl/src/nwfilter/nwfilter_driver.c
@@ -471,6 +471,15 @@ nwfilterTeardownFilter(virDomainNetDefPt
         virNWFilterTeardownFilter(net);
 }
 
+static void
+nwfilterFormatLeases(virBufferPtr buf,
+                     virNWFilterHashTablePtr vars,
+                     const char *ifname,
+                     const unsigned char *vmuuid,
+                     const unsigned char *mac)
+{
+    virNWFilterFormatLeases(buf, vars, ifname, vmuuid, mac);
+}
 
 static virNWFilterDriver nwfilterDriver = {
     .name = "nwfilter",
@@ -498,6 +507,7 @@ static virStateDriver stateDriver = {
 static virDomainConfNWFilterDriver domainNWFilterDriver = {
     .instantiateFilter = nwfilterInstantiateFilter,
     .teardownFilter = nwfilterTeardownFilter,
+    .formatLeases = nwfilterFormatLeases,
 };
 
 
Index: libvirt-acl/src/conf/nwfilter_ipaddrmap.c
===================================================================
--- libvirt-acl.orig/src/conf/nwfilter_ipaddrmap.c
+++ libvirt-acl/src/conf/nwfilter_ipaddrmap.c
@@ -122,6 +122,35 @@ remove_entry:
     return ret;
 }
 
+void
+virNWFilterIPAddrMapFormatIPAddrs(virBufferPtr buf,
+                                  const char *ifname,
+                                  const char *pre, const char *post)
+{
+    virNWFilterVarValuePtr val = NULL;
+
+    virMutexLock(&ipAddressMapLock);
+
+    val = virHashLookup(ipAddressMap->hashTable, ifname);
+    if (val) {
+        unsigned int card = virNWFilterVarValueGetCardinality(val);
+        unsigned int i;
+
+        for (i = 0; i < card; i++) {
+            const char *ipaddr = virNWFilterVarValueGetNthValue(val, i);
+
+            if (pre)
+                virBufferAdd(buf, pre, -1);
+            virBufferAdd(buf, ipaddr, -1);
+
+            if (post)
+                virBufferAdd(buf, post, -1);
+        }
+    }
+
+    virMutexUnlock(&ipAddressMapLock);
+}
+
 /* Get the list of IP addresses known to be in use by an interface
  *
  * This function returns NULL in case no IP address is known to be
Index: libvirt-acl/src/conf/nwfilter_ipaddrmap.h
===================================================================
--- libvirt-acl.orig/src/conf/nwfilter_ipaddrmap.h
+++ libvirt-acl/src/conf/nwfilter_ipaddrmap.h
@@ -26,6 +26,8 @@
 #ifndef __VIR_NWFILTER_IPADDRMAP_H
 # define __VIR_NWFILTER_IPADDRMAP_H
 
+# include "buf.h"
+
 int virNWFilterIPAddrMapInit(void);
 void virNWFilterIPAddrMapShutdown(void);
 
@@ -33,5 +35,8 @@ int virNWFilterIPAddrMapAddIPAddr(const 
 int virNWFilterIPAddrMapDelIPAddr(const char *ifname,
                                   const char *ipaddr);
 virNWFilterVarValuePtr virNWFilterIPAddrMapGetIPAddr(const char *ifname);
+void virNWFilterIPAddrMapFormatIPAddrs(virBufferPtr buf,
+                                       const char *ifname,
+                                       const char *pre, const char *post);
 
 #endif /* __VIR_NWFILTER_IPADDRMAP_H */
Index: libvirt-acl/src/nwfilter/nwfilter_learnipaddr.c
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_learnipaddr.c
+++ libvirt-acl/src/nwfilter/nwfilter_learnipaddr.c
@@ -771,6 +771,20 @@ virNWFilterLearnIPAddress(virNWFilterTec
 }
 #endif /* HAVE_LIBPCAP */
 
+/*
+ * Format the detected IP addresses for display in the domain's
+ * XML inside a <parameter name=... value=.../> XML node.
+ */
+void
+virNWFilterLearnFormatLeases(virBufferPtr buf,
+                             const char *ifname)
+{
+    virNWFilterIPAddrMapFormatIPAddrs(buf, ifname,
+                                      "<parameter name='"
+                                       NWFILTER_VARNAME_IP_LEASE
+                                       "' value='",
+                                      ",-1'/>\n");
+}
 
 /**
  * virNWFilterLearnInit
Index: libvirt-acl/src/nwfilter/nwfilter_learnipaddr.h
===================================================================
--- libvirt-acl.orig/src/nwfilter/nwfilter_learnipaddr.h
+++ libvirt-acl/src/nwfilter/nwfilter_learnipaddr.h
@@ -71,5 +71,7 @@ void virNWFilterUnlockIface(const char *
 int virNWFilterLearnInit(void);
 void virNWFilterLearnShutdown(void);
 void virNWFilterLearnThreadsTerminate(bool allowNewThreads);
+void virNWFilterLearnFormatLeases(virBufferPtr buf,
+                                  const char *ifname);
 
 #endif /* __NWFILTER_LEARNIPADDR_H */
Index: libvirt-acl/docs/formatnwfilter.html.in
===================================================================
--- libvirt-acl.orig/docs/formatnwfilter.html.in
+++ libvirt-acl/docs/formatnwfilter.html.in
@@ -446,6 +446,22 @@
     &lt;/interface&gt;
 </pre>
 
+    <p>
+       Once an IP address has been detected, the domain's interface XML
+       will display the detected IP address and its lease expiration time
+       in seconds. Note that the <code>IP_LEASE</code> variable is read-only
+       and cannot be set by the user.
+    </p>
+<pre>
+    &lt;interface type='bridge'&gt;
+      &lt;source bridge='virbr0'/&gt;
+      &lt;filterref filter='clean-traffic'&gt;
+        &lt;parameter name='CTRL_IP_LEARNING' value='dhcp'/&gt;
+        &lt;parameter name='IP_LEASE' value='192.168.122.100,200'/&gt;
+      &lt;/filterref&gt;
+    &lt;/interface&gt;
+</pre>
+
     <h3><a name="nwfelemsReservedVars">Reserved Variables</a></h3>
     <p>
       The following table lists reserved variables in use by libvirt.
@@ -481,6 +497,17 @@
          <td> CTRL_IP_LEARNING </td>
          <td> The choice of the IP address detection mode </td>
        </tr>
+       <tr>
+         <td> IP_LEASE </td>
+         <td> Read-only variable displaying the detected IP lease in the
+              format IP address,lease expiration time in seconds </td>
+       </tr>
+       <tr>
+         <td> IPV6_LEASE </td>
+         <td> Not currently implemented:
+              Read-only variable displaying the detected IPV6 lease in the
+              format IPV6 address,lease expiration time in seconds </td>
+       </tr>
       </table>
 
     <h2><a name="nwfelems">Element and attribute overview</a></h2>