Index: /trunk/src/VBox/Devices/Network/slirp/bootp.c
===================================================================
--- /trunk/src/VBox/Devices/Network/slirp/bootp.c	(revision 50671)
+++ /trunk/src/VBox/Devices/Network/slirp/bootp.c	(revision 50672)
@@ -42,4 +42,5 @@
  */
 #include <slirp.h>
+#include <libslirp.h>
 
 /** Entry in the table of known DHCP clients. */
@@ -698,4 +699,7 @@
      * within transaction), assuming that transaction can't be longer than 1 min.
      *
+     * @note: if we have notification update (HAVE_NOTIFICATION_FOR_DNS_UPDATE) 
+     * provided by host, we don't need implicitly re-initialize dns list. 
+     * 
      * @note: NATState::fUseHostResolver became (r89055) the flag signalling that Slirp 
      * wasn't able to fetch fresh host DNS info and fall down to use host-resolver, on one 
@@ -705,5 +709,6 @@
      * wanted by user ASAP (P here when host serialize its  configuration in files parsed by Slirp).
      */
-    if (   !pData->fUseHostResolverPermanent
+    if (   !HAVE_NOTIFICATION_FOR_DNS_UPDATE
+        && !pData->fUseHostResolverPermanent
         && (   pData->dnsLastUpdate == 0
             || curtime - pData->dnsLastUpdate > 60 * 1000 /* one minute */
@@ -716,4 +721,5 @@
             if (parameter_list[i] == RFC1533_DNS)
             {
+                /* XXX: How differs it from host Suspend/Resume? */
                 slirpReleaseDnsSettings(pData);
                 slirpInitializeDnsSettings(pData);
Index: /trunk/src/VBox/Devices/Network/slirp/slirp.c
===================================================================
--- /trunk/src/VBox/Devices/Network/slirp/slirp.c	(revision 50671)
+++ /trunk/src/VBox/Devices/Network/slirp/slirp.c	(revision 50672)
@@ -64,5 +64,13 @@
 
 #ifndef RT_OS_WINDOWS
-
+/** 
+ * XXX: It shouldn't be non-Windows specific.
+ * resolv_conf_parser.h client's structure isn't OS specific, it's just need to be generalized a
+ * a bit to replace slirp_state.h DNS server (domain) lists with rcp_state like structure.  
+ */
+# include "resolv_conf_parser.h"
+#endif
+
+#ifndef RT_OS_WINDOWS
 # define DO_ENGAGE_EVENT1(so, fdset, label)                        \
    do {                                                            \
@@ -2039,9 +2047,38 @@
 }
 
-
+/**
+ * @note: NATState::fUseHostResolver could be changed in bootp.c::dhcp_decode
+ * @note: this function is executed on GUI/VirtualBox or main/VBoxHeadless thread.
+ * @note: this function can potentially race with bootp.c::dhcp_decode (except Darwin)
+ */
 int slirp_host_network_configuration_change_strategy_selector(const PNATState pData)
 {
-    if (pData->fUseHostResolver) return VBOX_NAT_HNCE_HOSTRESOLVER;
-    if (pData->fUseDnsProxy) return VBOX_NAT_HNCE_DNSPROXY;
+    if (pData->fUseHostResolverPermanent) return VBOX_NAT_HNCE_HOSTRESOLVER;
+    if (pData->fUseDnsProxy) {
+#if HAVE_NOTIFICATION_FOR_DNS_UPDATE
+        /* We dont conflict with bootp.c::dhcp_decode */
+        struct rcp_state rcp_state;
+        int rc;
+        
+        rcp_state.rcps_flags |= RCPSF_IGNORE_IPV6;
+        rc = rcp_parse(&rcp_state, RESOLV_CONF_FILE);
+        LogRelFunc(("NAT: rcp_parse:%Rrc old domain:%s new domain:%s\n",
+                    rc, LIST_FIRST(&pData->pDomainList)->dd_pszDomain,
+                    rcp_state.rcps_domain));
+        if (   RT_FAILURE(rc)
+            || LIST_EMPTY(&pData->pDomainList))
+            return VBOX_NAT_HNCE_DNSPROXY;
+        
+        if (   rcp_state.rcps_domain
+            && strcmp(rcp_state.rcps_domain, LIST_FIRST(&pData->pDomainList)->dd_pszDomain) == 0)
+            return VBOX_NAT_HNCE_DNSPROXY;
+        else
+            return VBOX_NAT_HNCE_EXSPOSED_NAME_RESOLUTION_INFO; /* XXX: rename it */
+#else
+        /* copy domain name */
+        /* domain only compare with coy version */
+        return VBOX_NAT_HNCE_DNSPROXY;
+#endif
+    }
     return VBOX_NAT_HNCE_EXSPOSED_NAME_RESOLUTION_INFO;
 }