dhcpv6: add explicit dhcpv4o6 server address

Include the All_DHCP_Relay_Agents_and_Servers multicast address
in the option explicitly. It shouldn't be needed according
to RFC 7341 section 7.2 but ISC dhclient logs an error otherwise:

dhcp4-o-dhcp6-server: expecting at least 16 bytes; got 0

Signed-off-by: Mikael Magnusson <mikma@users.sourceforge.net>

diff --git a/src/dhcpv6.c b/src/dhcpv6.c
index cc068a35a8243de8da100b8a6fdb3b08a4231c42..00628cd219ae42cf25d76e1abd6757e79fbdaecc 100644 (file)
--- a/src/dhcpv6.c
+++ b/src/dhcpv6.c
@@ -397,10 +397,12 @@ static void handle_client_request(void *addr, void *data, size_t len,
        } search = {htons(DHCPV6_OPT_DNS_DOMAIN), htons(search_len)};
 
 
-       struct __attribute__((packed)) {
+       struct __attribute__((packed)) dhcpv4o6_server {
                uint16_t type;
                uint16_t len;
-       } dhcpv4o6_server = {htons(DHCPV6_OPT_4O6_SERVER), 0};
+               struct in6_addr addr;
+       } dhcpv4o6_server = {htons(DHCPV6_OPT_4O6_SERVER), htons(sizeof(struct in6_addr)),
+                       IN6ADDR_ANY_INIT};
 
        struct dhcpv6_cer_id cerid = {
 #ifdef EXT_CER_ID
@@ -505,11 +507,28 @@ static void handle_client_request(void *addr, void *data, size_t len,
                } else if (otype == DHCPV6_OPT_ORO) {
                        for (int i=0; i < olen/2; i++) {
                                uint16_t option = ntohs(((uint16_t *)odata)[i]);
+
                                switch (option) {
 #ifdef DHCPV4_SUPPORT
                                case DHCPV6_OPT_4O6_SERVER:
-                                       if (iface->dhcpv4)
+                                       if (iface->dhcpv4) {
+                                               /* According to RFC 7341, 7.2. DHCP 4o6 Server Address Option Format:
+                                                * This option may also carry no IPv6 addresses, which instructs the
+                                                * client to use the All_DHCP_Relay_Agents_and_Servers multicast address
+                                                * as the destination address.
+                                                *
+                                                * The ISC dhclient logs a missing IPv6 address as an error but seems to
+                                                * work anyway:
+                                                * dhcp4-o-dhcp6-server: expecting at least 16 bytes; got 0
+                                                *
+                                                * Include the All_DHCP_Relay_Agents_and_Servers multicast address
+                                                * to make it explicit which address to use. */
+                                               struct dhcpv4o6_server *server = iov[IOV_DHCPV4O6_SERVER].iov_base;
+
+                                               inet_pton(AF_INET6, ALL_DHCPV6_RELAYS, &server->addr);
+
                                                iov[IOV_DHCPV4O6_SERVER].iov_len = sizeof(dhcpv4o6_server);
+                                       }
                                        break;
 #endif /* DHCPV4_SUPPORT */
                                default: