Index: sbin/dumpon/dumpon.c
===================================================================
--- sbin/dumpon/dumpon.c
+++ sbin/dumpon/dumpon.c
@@ -547,6 +547,22 @@
 		if (strcmp(argv[0], "off") == 0) {
 			rflag = true;
 			dev = _PATH_DEVNULL;
+
+			/*
+			 * Netdump has its own configuration tracking that
+			 * is not removed when using /dev/null.
+			 */
+			fd = open(_PATH_NETDUMP, O_RDONLY);
+			if (fd != -1) {
+				bzero(&ndconf, sizeof(ndconf));
+				ndconf.kda_index = KDA_REMOVE_ALL;
+				ndconf.kda_af = AF_INET;
+				error = ioctl(fd, DIOCSKERNELDUMP, &ndconf);
+				if (error != 0)
+					err(1, "ioctl(%s, DIOCSKERNELDUMP)",
+					    _PATH_NETDUMP);
+				close(fd);
+			}
 		} else
 			dev = argv[0];
 		netdump = false;