Index: qemu/vl.c
===================================================================
--- qemu/vl.c.orig
+++ qemu/vl.c
@@ -229,6 +229,7 @@ const char *vnc_display;
 #endif
 int acpi_enabled = 1;
 int fd_bootchk = 1;
+int slirp_nooutgoing = 0;
 int no_reboot = 0;
 int no_shutdown = 0;
 int cursor_hide = 1;
@@ -8566,6 +8567,7 @@ enum {
     QEMU_OPTION_append,
     QEMU_OPTION_initrd,
 
+    QEMU_OPTION_nooutgoing,
     QEMU_OPTION_S,
     QEMU_OPTION_s,
     QEMU_OPTION_p,
@@ -8672,6 +8674,7 @@ const QEMUOption qemu_options[] = {
     { "append", HAS_ARG, QEMU_OPTION_append },
     { "initrd", HAS_ARG, QEMU_OPTION_initrd },
 
+    { "nooutgoing", HAS_ARG, QEMU_OPTION_nooutgoing },
     { "S", 0, QEMU_OPTION_S },
     { "s", 0, QEMU_OPTION_s },
     { "p", HAS_ARG, QEMU_OPTION_p },
@@ -9460,6 +9463,14 @@ int main(int argc, char **argv)
             case QEMU_OPTION_bios:
                 bios_name = optarg;
                 break;
+            case QEMU_OPTION_nooutgoing:
+                slirp_nooutgoing = inet_addr(optarg);
+                if (slirp_nooutgoing == INADDR_NONE) {
+                    printf("Invalid address: %s.\nOnly addresses of the format "
+                           "xxx.xxx.xxx.xxx are supported.\n", optarg);
+                    exit(1);
+                }
+                break;
             case QEMU_OPTION_S:
                 autostart = 0;
                 break;
Index: qemu/slirp/tcp_subr.c
===================================================================
--- qemu/slirp/tcp_subr.c.orig
+++ qemu/slirp/tcp_subr.c
@@ -379,6 +379,9 @@ tcp_sockclosed(tp)
  * nonblocking.  Connect returns after the SYN is sent, and does
  * not wait for ACK+SYN.
  */
+
+extern int slirp_nooutgoing;
+
 int tcp_fconnect(so)
      struct socket *so;
 {
@@ -387,6 +390,11 @@ int tcp_fconnect(so)
   DEBUG_CALL("tcp_fconnect");
   DEBUG_ARG("so = %lx", (long )so);
 
+  if (slirp_nooutgoing) {
+    errno = EHOSTUNREACH;
+    return -1;
+  }
+
   if( (ret=so->s=socket(AF_INET,SOCK_STREAM,0)) >= 0) {
     int opt, s=so->s;
     struct sockaddr_in addr;
@@ -481,6 +489,13 @@ tcp_connect(inso)
 		tcp_close(sototcpcb(so)); /* This will sofree() as well */
 		return;
 	}
+
+	if (slirp_nooutgoing && addr.sin_addr.s_addr != slirp_nooutgoing) {
+		tcp_close(sototcpcb(so)); /* This will sofree() as well */
+		close(s);
+		return;
+	}
+
 	fd_nonblock(s);
 	opt = 1;
 	setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *)&opt,sizeof(int));
@@ -491,6 +506,7 @@ tcp_connect(inso)
 
 	so->so_fport = addr.sin_port;
 	so->so_faddr = addr.sin_addr;
+
 	/* Translate connections from localhost to the real hostname */
 	if (so->so_faddr.s_addr == 0 || so->so_faddr.s_addr == loopback_addr.s_addr)
 	   so->so_faddr = alias_addr;
Index: qemu/slirp/socket.c
===================================================================
--- qemu/slirp/socket.c.orig
+++ qemu/slirp/socket.c
@@ -484,6 +484,8 @@ sorecvfrom(so)
 	} /* if ping packet */
 }
 
+extern int slirp_nooutgoing;
+
 /*
  * sendto() a socket
  */
@@ -517,6 +519,12 @@ sosendto(so, m)
 
 	DEBUG_MISC((dfd, " sendto()ing, addr.sin_port=%d, addr.sin_addr.s_addr=%.16s\n", ntohs(addr.sin_port), inet_ntoa(addr.sin_addr)));
 
+	/* Only allow DNS requests */
+	if (slirp_nooutgoing && ntohs(addr.sin_port) != 53) {
+		errno = EHOSTUNREACH;
+		return -1;
+	}
+
 	/* Don't care what port we get */
 	ret = sendto(so->s, m->m_data, m->m_len, 0,
 		     (struct sockaddr *)&addr, sizeof (struct sockaddr));