diff -Nru isc-dhcp-4.3.5/debian/changelog isc-dhcp-4.3.5/debian/changelog
--- isc-dhcp-4.3.5/debian/changelog	2017-09-14 18:41:06.000000000 -0400
+++ isc-dhcp-4.3.5/debian/changelog	2017-10-12 08:48:06.000000000 -0400
@@ -1,3 +1,10 @@
+isc-dhcp (4.3.5-3ubuntu4) bionic; urgency=medium
+
+  * dhclient-script.linux: handle empty case also when waiting for ipv6 link local DAD.
+    (LP: #1718568)
+
+ -- Dan Streetman <dan.streetman@canonical.com>  Thu, 12 Oct 2017 08:48:06 -0400
+
 isc-dhcp (4.3.5-3ubuntu3) bionic; urgency=medium
 
   * No-change rebuild against the new SOVERs of bind9 libraries.
diff -Nru isc-dhcp-4.3.5/debian/dhclient-script.linux isc-dhcp-4.3.5/debian/dhclient-script.linux
--- isc-dhcp-4.3.5/debian/dhclient-script.linux	2017-09-14 18:36:37.000000000 -0400
+++ isc-dhcp-4.3.5/debian/dhclient-script.linux	2017-10-12 08:48:06.000000000 -0400
@@ -165,12 +165,18 @@
             error "$dev: checking for link-local addresses failed";
             return 1
         }
+        # another note: the output may be empty if the link local tentative addr
+        # isn't up just yet, so we need to make sure there is at least one 'inet6'
+        # match before returning success.  We need to keep checking for both
+        # 'tentative' case and default (no inet6 address) case. (LP: #1718568)
+        # Don't reorder tentative/inet6 - we need to check for tentative first.
         case " $out " in
             *\ dadfailed\ *)
                 error "$dev: ipv6 dad failed."
                 return 1;;
             *\ tentative\ *) :;;
-            *) return 0;;
+            *\ inet6\ *) return 0;;
+            *) :;;
         esac
         [ $n -lt $attempts ] || {
             error "$dev: time out waiting for permanent link-local address"