diff -pru dhcp-4.4.1/client/dhc6.c client/dhc6.c
--- dhcp-4.4.1/client/dhc6.c	2018-02-21 15:30:46.000000000 +0100
+++ client/dhc6.c	2018-08-04 03:17:56.477869000 +0200
@@ -5744,7 +5744,8 @@ make_client6_options(struct client_state
 	 */
 	if ((oc = lookup_option(&dhcpv6_universe, *op,
 				D6O_CLIENTID)) == NULL) {
-		if (!option_cache(&oc, &default_duid, NULL, clientid_option,
+		if (default_duid.len == 0 ||
+		    !option_cache(&oc, &default_duid, NULL, clientid_option,
 				  MDL))
 			log_fatal("Failure assembling a DUID.");
 
diff -pru dhcp-4.4.1/client/dhclient.c client/dhclient.c
--- dhcp-4.4.1/client/dhclient.c	2018-02-21 15:30:46.000000000 +0100
+++ client/dhclient.c	2018-08-04 03:17:56.486690000 +0200
@@ -849,8 +849,8 @@ main(int argc, char **argv) {
 			if (default_duid.buffer != NULL)
 				data_string_forget(&default_duid, MDL);
 
-			form_duid(&default_duid, MDL);
-			write_duid(&default_duid);
+			if (form_duid(&default_duid, MDL) == ISC_R_SUCCESS)
+				write_duid(&default_duid);
 		}
 	}
 
@@ -3599,7 +3599,7 @@ write_options(struct client_state *clien
  * is not how it is intended.  Upcoming rearchitecting the client should
  * address this "one daemon model."
  */
-void
+isc_result_t
 form_duid(struct data_string *duid, const char *file, int line)
 {
 	struct interface_info *ip;
@@ -3612,6 +3612,15 @@ form_duid(struct data_string *duid, cons
 	if (ip == NULL)
 		log_fatal("Impossible condition at %s:%d.", MDL);
 
+	while (ip && ip->hw_address.hbuf[0] == HTYPE_RESERVED) {
+		/* Try the other interfaces */
+		log_debug("Cannot form default DUID from interface %s.", ip->name);
+		ip = ip->next;
+	}
+	if (ip == NULL) {
+		return ISC_R_UNEXPECTED;
+	}
+
 	if ((ip->hw_address.hlen == 0) ||
 	    (ip->hw_address.hlen > sizeof(ip->hw_address.hbuf)))
 		log_fatal("Impossible hardware address length at %s:%d.", MDL);
@@ -3657,6 +3666,7 @@ form_duid(struct data_string *duid, cons
 		log_info("Created duid %s.", str);
 		dfree(str, MDL);
 	}
+	return ISC_R_SUCCESS;
 }
 
 /* Write the default DUID to the lease store. */
diff -pru dhcp-4.4.1/common/bpf.c common/bpf.c
--- dhcp-4.4.1/common/bpf.c	2018-02-21 15:30:46.000000000 +0100
+++ common/bpf.c	2018-08-04 03:17:56.489728000 +0200
@@ -650,6 +650,27 @@ get_hw_addr(const char *name, struct har
                         memcpy(&hw->hbuf[1], LLADDR(sa), sa->sdl_alen);
                         break;
 #endif /* IFT_FDDI */
+#if defined(IFT_PPP)
+		case IFT_PPP:
+#endif
+#if defined(IFT_PROPVIRTUAL)
+		case IFT_PROPVIRTUAL: /* netgraph */
+#endif
+#if defined(IFT_PPP) || defined(IFT_PROPVIRTUAL)
+			if (local_family != AF_INET6)
+				log_fatal("Unsupported device type %d for \"%s\"",
+					  sa->sdl_type, name);
+			hw->hlen = 0;
+			hw->hbuf[0] = HTYPE_RESERVED;
+			/* 0xdeadbeef should never occur on the wire, and is a signature that
+			 * something went wrong.
+			 */
+			hw->hbuf[1] = 0xde;
+			hw->hbuf[2] = 0xad;
+			hw->hbuf[3] = 0xbe;
+			hw->hbuf[4] = 0xef;
+			break;
+#endif
                 default:
                         log_fatal("Unsupported device type %d for \"%s\"",
                                   sa->sdl_type, name);
diff -pru dhcp-4.4.1/common/lpf.c common/lpf.c
--- dhcp-4.4.1/common/lpf.c	2018-02-21 15:30:46.000000000 +0100
+++ common/lpf.c	2018-08-04 03:17:56.492470000 +0200
@@ -563,6 +563,22 @@ get_hw_addr(const char *name, struct har
 			hw->hbuf[0] = HTYPE_FDDI;
 			memcpy(&hw->hbuf[1], sa->sa_data, 6);
 			break;
+#if defined(ARPHRD_PPP)
+		case ARPHRD_PPP:
+			if (local_family != AF_INET6)
+				log_fatal("Unsupported device type %d for \"%s\"",
+					  sa->sa_family, name);
+			hw->hlen = 0;
+			hw->hbuf[0] = HTYPE_RESERVED;
+			/* 0xdeadbeef should never occur on the wire, and is a signature that
+			 * something went wrong.
+			 */
+			hw->hbuf[1] = 0xde;
+			hw->hbuf[2] = 0xad;
+			hw->hbuf[3] = 0xbe;
+			hw->hbuf[4] = 0xef;
+			break;
+#endif
 		default:
 			log_fatal("Unsupported device type %ld for \"%s\"",
 				  (long int)sa->sa_family, name);
diff -pru dhcp-4.4.1/includes/dhcp.h includes/dhcp.h
--- dhcp-4.4.1/includes/dhcp.h	2018-02-21 15:30:46.000000000 +0100
+++ includes/dhcp.h	2018-08-04 03:17:56.494943000 +0200
@@ -79,6 +79,7 @@ struct dhcp_packet {
 #define HTYPE_IPMP       255            /* IPMP - random hw address - there
 					 * is no standard for this so we
 					 * just steal a type            */
+#define HTYPE_RESERVED	0		/* RFC 5494 */
 
 /* Magic cookie validating dhcp options field (and bootp vendor
    extensions field). */
diff -pru dhcp-4.4.1/includes/dhcpd.h includes/dhcpd.h
--- dhcp-4.4.1/includes/dhcpd.h	2018-02-21 15:30:46.000000000 +0100
+++ includes/dhcpd.h	2018-08-04 03:17:56.503199000 +0200
@@ -3047,7 +3047,7 @@ void client_dns_remove(struct client_sta
 
 void dhcpv4_client_assignments(void);
 void dhcpv6_client_assignments(void);
-void form_duid(struct data_string *duid, const char *file, int line);
+isc_result_t form_duid(struct data_string *duid, const char *file, int line);
 
 void dhcp4o6_start(void);
 
diff -pru dhcp-4.4.1/server/dhcpv6.c server/dhcpv6.c
--- dhcp-4.4.1/server/dhcpv6.c	2018-02-21 15:30:46.000000000 +0100
+++ server/dhcpv6.c	2018-08-04 03:17:56.513816000 +0200
@@ -482,6 +482,9 @@ generate_new_server_duid(void) {
 		if (p->hw_address.hlen > 0) {
 			break;
 		}
+		if (p->next == NULL && p->hw_address.hbuf[0] == HTYPE_RESERVED) {
+			log_error("Can not generate DUID from interfaces which do not have hardware addresses, please configure server-duid!");
+		}
 	}
 	if (p == NULL) {
 		return ISC_R_UNEXPECTED;