src/dhcpv6.c

   1 /**
   2  * Copyright (C) 2012-2013 Steven Barth <steven@midlink.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License v2 as published by
   6  * the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  *
  14  */
  15
  16 #include <errno.h>
  17 #include <unistd.h>
  18 #include <stddef.h>
  19 #include <resolv.h>
  20 #include <sys/timerfd.h>
  21
  22 #include "odhcpd.h"
  23 #include "dhcpv6.h"
  24
  25
  26 static void relay_client_request(struct sockaddr_in6 *source,
  27                 const void *data, size_t len, struct interface *iface);
  28 static void relay_server_response(uint8_t *data, size_t len);
  29
  30 static void handle_dhcpv6(void *addr, void *data, size_t len,
  31                 struct interface *iface, void *dest);
  32 static void handle_client_request(void *addr, void *data, size_t len,
  33                 struct interface *iface, void *dest_addr);
  34
  35
  36
  37 // Create socket and register events
  38 int init_dhcpv6(void)
  39 {
  40         dhcpv6_ia_init();
  41         return 0;
  42 }
  43
  44
  45 int setup_dhcpv6_interface(struct interface *iface, bool enable)
  46 {
  47         if (iface->dhcpv6_event.uloop.fd > 0) {
  48                 uloop_fd_delete(&iface->dhcpv6_event.uloop);
  49                 close(iface->dhcpv6_event.uloop.fd);
  50                 iface->dhcpv6_event.uloop.fd = -1;
  51         }
  52
  53         // Configure multicast settings
  54         if (enable && iface->dhcpv6 && !iface->master) {
  55                 int sock = socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  56                 if (sock < 0) {
  57                         syslog(LOG_ERR, "Failed to create DHCPv6 server socket: %s",
  58                                         strerror(errno));
  59                         return -1;
  60                 }
  61
  62                 // Basic IPv6 configuration
  63                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, iface->ifname, strlen(iface->ifname));
  64
  65                 int val = 1;
  66                 setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
  67                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  68                 setsockopt(sock, IPPROTO_IPV6, IPV6_RECVPKTINFO, &val, sizeof(val));
  69
  70                 val = DHCPV6_HOP_COUNT_LIMIT;
  71                 setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &val, sizeof(val));
  72
  73                 val = 0;
  74                 setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &val, sizeof(val));
  75
  76                 struct sockaddr_in6 bind_addr = {AF_INET6, htons(DHCPV6_SERVER_PORT),
  77                                         0, IN6ADDR_ANY_INIT, 0};
  78
  79                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
  80                         syslog(LOG_ERR, "Failed to open DHCPv6 server socket: %s",
  81                                         strerror(errno));
  82                         return -1;
  83                 }
  84
  85                 struct ipv6_mreq relay = {ALL_DHCPV6_RELAYS, iface->ifindex};
  86                 struct ipv6_mreq server = {ALL_DHCPV6_SERVERS, iface->ifindex};
  87                 setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &relay, sizeof(relay));
  88
  89                 if (iface->dhcpv6 == RELAYD_SERVER)
  90                         setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &server, sizeof(server));
  91
  92                 iface->dhcpv6_event.uloop.fd = sock;
  93                 iface->dhcpv6_event.handle_dgram = handle_dhcpv6;
  94                 odhcpd_register(&iface->dhcpv6_event);
  95         }
  96
  97         return setup_dhcpv6_ia_interface(iface, enable);
  98 }
  99
 100 enum {
 101         IOV_NESTED = 0,
 102         IOV_DEST,
 103         IOV_MAXRT,
 104 #define IOV_STAT IOV_MAXRT
 105         IOV_DNS,
 106         IOV_DNS_ADDR,
 107         IOV_SEARCH,
 108         IOV_SEARCH_DOMAIN,
 109         IOV_PDBUF,
 110 #define IOV_REFRESH IOV_PDBUF
 111         IOV_CERID,
 112         IOV_DHCPV6_RAW,
 113         IOV_RELAY_MSG,
 114         IOV_TOTAL
 115 };
 116
 117 static void handle_nested_message(uint8_t *data, size_t len,
 118                 uint8_t **opts, uint8_t **end, struct iovec iov[IOV_TOTAL - 1])
 119 {
 120         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 121         if (iov[IOV_NESTED].iov_base == NULL) {
 122                 iov[IOV_NESTED].iov_base = data;
 123                 iov[IOV_NESTED].iov_len = len;
 124         }
 125
 126         if (len < sizeof(struct dhcpv6_client_header))
 127                 return;
 128
 129         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW) {
 130                 iov[IOV_NESTED].iov_len = data - (uint8_t*)iov[IOV_NESTED].iov_base;
 131                 struct dhcpv6_client_header *hdr = (void*)data;
 132                 *opts = (uint8_t*)&hdr[1];
 133                 *end = data + len;
 134                 return;
 135         }
 136
 137         uint16_t otype, olen;
 138         uint8_t *odata;
 139         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 140                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 141                         iov[IOV_RELAY_MSG].iov_base = odata + olen;
 142                         iov[IOV_RELAY_MSG].iov_len = (((uint8_t*)iov[IOV_NESTED].iov_base) +
 143                                         iov[IOV_NESTED].iov_len) - (odata + olen);
 144                         handle_nested_message(odata, olen, opts, end, iov);
 145                         return;
 146                 }
 147         }
 148 }
 149
 150
 151 static void update_nested_message(uint8_t *data, size_t len, ssize_t pdiff)
 152 {
 153         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 154         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW)
 155                 return;
 156
 157         hdr->msg_type = DHCPV6_MSG_RELAY_REPL;
 158
 159         uint16_t otype, olen;
 160         uint8_t *odata;
 161         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 162                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 163                         olen += pdiff;
 164                         odata[-2] = (olen >> 8) & 0xff;
 165                         odata[-1] = olen & 0xff;
 166                         update_nested_message(odata, olen - pdiff, pdiff);
 167                         return;
 168                 }
 169         }
 170 }
 171
 172 // Simple DHCPv6-server for information requests
 173 static void handle_client_request(void *addr, void *data, size_t len,
 174                 struct interface *iface, void *dest_addr)
 175 {
 176         struct dhcpv6_client_header *hdr = data;
 177
 178         if (len < sizeof(*hdr))
 179                 return;
 180
 181         syslog(LOG_NOTICE, "Got DHCPv6 request");
 182
 183         // Construct reply message
 184         struct __attribute__((packed)) {
 185                 uint8_t msg_type;
 186                 uint8_t tr_id[3];
 187                 uint16_t serverid_type;
 188                 uint16_t serverid_length;
 189                 uint16_t duid_type;
 190                 uint16_t hardware_type;
 191                 uint8_t mac[6];
 192                 uint16_t clientid_type;
 193                 uint16_t clientid_length;
 194                 uint8_t clientid_buf[130];
 195         } dest = {
 196                 .msg_type = DHCPV6_MSG_REPLY,
 197                 .serverid_type = htons(DHCPV6_OPT_SERVERID),
 198                 .serverid_length = htons(10),
 199                 .duid_type = htons(3),
 200                 .hardware_type = htons(1),
 201                 .clientid_type = htons(DHCPV6_OPT_CLIENTID),
 202                 .clientid_buf = {0}
 203         };
 204         odhcpd_get_mac(iface, dest.mac);
 205
 206         struct __attribute__((packed)) {
 207                 uint16_t type;
 208                 uint16_t len;
 209                 uint32_t value;
 210         } maxrt = {htons(DHCPV6_OPT_SOL_MAX_RT), htons(sizeof(maxrt) - 4),
 211                         htonl(60)};
 212
 213         struct __attribute__((packed)) {
 214                 uint16_t type;
 215                 uint16_t len;
 216                 uint16_t value;
 217         } stat = {htons(DHCPV6_OPT_STATUS), htons(sizeof(stat) - 4),
 218                         htons(DHCPV6_STATUS_USEMULTICAST)};
 219
 220         struct __attribute__((packed)) {
 221                 uint16_t type;
 222                 uint16_t len;
 223                 uint32_t value;
 224         } refresh = {htons(DHCPV6_OPT_INFO_REFRESH), htons(sizeof(uint32_t)),
 225                         htonl(600)};
 226
 227         struct odhcpd_ipaddr ipaddr;
 228         struct in6_addr *dns_addr = iface->dns;
 229         size_t dns_cnt = iface->dns_cnt;
 230
 231         if (dns_cnt == 0 && odhcpd_get_interface_addresses(iface->ifindex, &ipaddr, 1) == 1) {
 232                 dns_addr = &ipaddr.addr;
 233                 dns_cnt = 1;
 234         }
 235
 236         struct {
 237                 uint16_t type;
 238                 uint16_t len;
 239         } dns = {htons(DHCPV6_OPT_DNS_SERVERS), htons(dns_cnt * sizeof(*dns_addr))};
 240
 241
 242
 243         // DNS Search options
 244         uint8_t search_buf[256], *search_domain = iface->search;
 245         size_t search_len = iface->search_len;
 246
 247         if (!search_domain && !res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 248                 int len = dn_comp(_res.dnsrch[0], search_buf,
 249                                 sizeof(search_buf), NULL, NULL);
 250                 if (len > 0) {
 251                         search_domain = search_buf;
 252                         search_len = len;
 253                 }
 254         }
 255
 256         struct {
 257                 uint16_t type;
 258                 uint16_t len;
 259         } search = {htons(DHCPV6_OPT_DNS_DOMAIN), htons(search_len)};
 260
 261
 262         struct dhcpv6_cer_id cerid = {
 263 #ifdef EXT_CER_ID
 264                 .type = htons(EXT_CER_ID),
 265 #endif
 266                 .len = htons(36),
 267                 .addr = iface->dhcpv6_pd_cer,
 268         };
 269
 270
 271         uint8_t pdbuf[512];
 272         struct iovec iov[IOV_TOTAL] = {
 273                 [IOV_NESTED] = {NULL, 0},
 274                 [IOV_DEST] = {&dest, (uint8_t*)&dest.clientid_type - (uint8_t*)&dest},
 275                 [IOV_MAXRT] = {&maxrt, sizeof(maxrt)},
 276                 [IOV_DNS] = {&dns, (dns_cnt) ? sizeof(dns) : 0},
 277                 [IOV_DNS_ADDR] = {dns_addr, dns_cnt * sizeof(*dns_addr)},
 278                 [IOV_SEARCH] = {&search, (search_len) ? sizeof(search) : 0},
 279                 [IOV_SEARCH_DOMAIN] = {search_domain, search_len},
 280                 [IOV_PDBUF] = {pdbuf, 0},
 281                 [IOV_CERID] = {&cerid, 0},
 282                 [IOV_DHCPV6_RAW] = {iface->dhcpv6_raw, iface->dhcpv6_raw_len},
 283                 [IOV_RELAY_MSG] = {NULL, 0}
 284         };
 285
 286         uint8_t *opts = (uint8_t*)&hdr[1], *opts_end = (uint8_t*)data + len;
 287         if (hdr->msg_type == DHCPV6_MSG_RELAY_FORW)
 288                 handle_nested_message(data, len, &opts, &opts_end, iov);
 289
 290         memcpy(dest.tr_id, &opts[-3], sizeof(dest.tr_id));
 291
 292         if (opts[-4] == DHCPV6_MSG_ADVERTISE || opts[-4] == DHCPV6_MSG_REPLY || opts[-4] == DHCPV6_MSG_RELAY_REPL)
 293                 return;
 294
 295         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 296                 (opts[-4] == DHCPV6_MSG_SOLICIT || opts[-4] == DHCPV6_MSG_CONFIRM ||
 297                  opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST))
 298                 return;
 299
 300         if (opts[-4] == DHCPV6_MSG_SOLICIT) {
 301                 dest.msg_type = DHCPV6_MSG_ADVERTISE;
 302         } else if (opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST) {
 303                 iov[IOV_REFRESH].iov_base = &refresh;
 304                 iov[IOV_REFRESH].iov_len = sizeof(refresh);
 305
 306                 // Return inf max rt option in reply to information request
 307                 maxrt.type = htons(DHCPV6_OPT_INF_MAX_RT);
 308         }
 309
 310         // Go through options and find what we need
 311         uint16_t otype, olen;
 312         uint8_t *odata;
 313         dhcpv6_for_each_option(opts, opts_end, otype, olen, odata) {
 314                 if (otype == DHCPV6_OPT_CLIENTID && olen <= 130) {
 315                         dest.clientid_length = htons(olen);
 316                         memcpy(dest.clientid_buf, odata, olen);
 317                         iov[IOV_DEST].iov_len += 4 + olen;
 318                 } else if (otype == DHCPV6_OPT_SERVERID) {
 319                         if (olen != ntohs(dest.serverid_length) ||
 320                                         memcmp(odata, &dest.duid_type, olen))
 321                                 return; // Not for us
 322                 } else if (iface->filter_class && otype == DHCPV6_OPT_USER_CLASS) {
 323                         uint8_t *c = odata, *cend = &odata[olen];
 324                         for (; &c[2] <= cend && &c[2 + (c[0] << 8) + c[1]] <= cend; c = &c[2 + (c[0] << 8) + c[1]]) {
 325                                 size_t elen = strlen(iface->filter_class);
 326                                 if (((((size_t)c[0]) << 8) | c[1]) == elen && !memcmp(&c[2], iface->filter_class, elen))
 327                                         return; // Ignore from homenet
 328                         }
 329                 } else if (otype == DHCPV6_OPT_IA_PD) {
 330 #ifdef EXT_CER_ID
 331                         iov[IOV_CERID].iov_len = sizeof(cerid);
 332
 333                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)) {
 334                                 struct odhcpd_ipaddr addrs[32];
 335                                 ssize_t len = odhcpd_get_interface_addresses(0, addrs,
 336                                                 sizeof(addrs) / sizeof(*addrs));
 337
 338                                 for (ssize_t i = 0; i < len; ++i)
 339                                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)
 340                                                         || memcmp(&addrs[i].addr, &cerid.addr, sizeof(cerid.addr)) < 0)
 341                                                 cerid.addr = addrs[i].addr;
 342                         }
 343 #endif
 344                 }
 345         }
 346
 347         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 348                 (opts[-4] == DHCPV6_MSG_REQUEST || opts[-4] == DHCPV6_MSG_RENEW ||
 349                  opts[-4] == DHCPV6_MSG_RELEASE || opts[-4] == DHCPV6_MSG_DECLINE)) {
 350                 iov[IOV_STAT].iov_base = &stat;
 351                 iov[IOV_STAT].iov_len = sizeof(stat);
 352
 353                 for (ssize_t i = IOV_STAT + 1; i < IOV_TOTAL; ++i)
 354                         iov[i].iov_len = 0;
 355
 356                 odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 357                 return;
 358         }
 359
 360         if (opts[-4] != DHCPV6_MSG_INFORMATION_REQUEST) {
 361                 ssize_t ialen = dhcpv6_handle_ia(pdbuf, sizeof(pdbuf), iface, addr, &opts[-4], opts_end);
 362                 iov[IOV_PDBUF].iov_len = ialen;
 363                 if (ialen < 0 || (ialen == 0 && (opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_CONFIRM)))
 364                         return;
 365         }
 366
 367         if (iov[IOV_NESTED].iov_len > 0) // Update length
 368                 update_nested_message(data, len, iov[IOV_DEST].iov_len + iov[IOV_MAXRT].iov_len +
 369                                 iov[IOV_DNS].iov_len + iov[IOV_DNS_ADDR].iov_len +
 370                                 iov[IOV_SEARCH].iov_len + iov[IOV_SEARCH_DOMAIN].iov_len +
 371                                 iov[IOV_PDBUF].iov_len + iov[IOV_CERID].iov_len +
 372                                 iov[IOV_DHCPV6_RAW].iov_len - (4 + opts_end - opts));
 373
 374         odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 375 }
 376
 377
 378 // Central DHCPv6-relay handler
 379 static void handle_dhcpv6(void *addr, void *data, size_t len,
 380                 struct interface *iface, void *dest_addr)
 381 {
 382         if (iface->dhcpv6 == RELAYD_SERVER) {
 383                 handle_client_request(addr, data, len, iface, dest_addr);
 384         } else if (iface->dhcpv6 == RELAYD_RELAY) {
 385                 if (iface->master)
 386                         relay_server_response(data, len);
 387                 else
 388                         relay_client_request(addr, data, len, iface);
 389         }
 390 }
 391
 392
 393 // Relay server response (regular relay server handling)
 394 static void relay_server_response(uint8_t *data, size_t len)
 395 {
 396         // Information we need to gather
 397         uint8_t *payload_data = NULL;
 398         size_t payload_len = 0;
 399         int32_t ifaceidx = 0;
 400         struct sockaddr_in6 target = {AF_INET6, htons(DHCPV6_CLIENT_PORT),
 401                 0, IN6ADDR_ANY_INIT, 0};
 402
 403         syslog(LOG_NOTICE, "Got a DHCPv6-reply");
 404
 405         int otype, olen;
 406         uint8_t *odata, *end = data + len;
 407
 408         // Relay DHCPv6 reply from server to client
 409         struct dhcpv6_relay_header *h = (void*)data;
 410         if (len < sizeof(*h) || h->msg_type != DHCPV6_MSG_RELAY_REPL)
 411                 return;
 412
 413         memcpy(&target.sin6_addr, &h->peer_address,
 414                         sizeof(struct in6_addr));
 415
 416         // Go through options and find what we need
 417         dhcpv6_for_each_option(h->options, end, otype, olen, odata) {
 418                 if (otype == DHCPV6_OPT_INTERFACE_ID
 419                                 && olen == sizeof(ifaceidx)) {
 420                         memcpy(&ifaceidx, odata, sizeof(ifaceidx));
 421                 } else if (otype == DHCPV6_OPT_RELAY_MSG) {
 422                         payload_data = odata;
 423                         payload_len = olen;
 424                 }
 425         }
 426
 427         // Invalid interface-id or basic payload
 428         struct interface *iface = odhcpd_get_interface_by_index(ifaceidx);
 429         if (!iface || iface->master || !payload_data || payload_len < 4)
 430                 return;
 431
 432         bool is_authenticated = false;
 433         struct in6_addr *dns_ptr = NULL;
 434         size_t dns_count = 0;
 435
 436         // If the payload is relay-reply we have to send to the server port
 437         if (payload_data[0] == DHCPV6_MSG_RELAY_REPL) {
 438                 target.sin6_port = htons(DHCPV6_SERVER_PORT);
 439         } else { // Go through the payload data
 440                 struct dhcpv6_client_header *h = (void*)payload_data;
 441                 end = payload_data + payload_len;
 442
 443                 dhcpv6_for_each_option(&h[1], end, otype, olen, odata) {
 444                         if (otype == DHCPV6_OPT_DNS_SERVERS && olen >= 16) {
 445                                 dns_ptr = (struct in6_addr*)odata;
 446                                 dns_count = olen / 16;
 447                         } else if (otype == DHCPV6_OPT_AUTH) {
 448                                 is_authenticated = true;
 449                         }
 450                 }
 451         }
 452
 453         // Rewrite DNS servers if requested
 454         if (iface->always_rewrite_dns && dns_ptr && dns_count > 0) {
 455                 if (is_authenticated)
 456                         return; // Impossible to rewrite
 457
 458                 struct odhcpd_ipaddr ip;
 459                 const struct in6_addr *rewrite = iface->dns;
 460                 size_t rewrite_cnt = iface->dns_cnt;
 461
 462                 if (rewrite_cnt == 0) {
 463                         if (odhcpd_get_interface_addresses(iface->ifindex, &ip, 1) < 1)
 464                                 return; // Unable to get interface address
 465
 466                         rewrite = &ip.addr;
 467                         rewrite_cnt = 1;
 468                 }
 469
 470                 // Copy over any other addresses
 471                 for (size_t i = 0; i < dns_count; ++i) {
 472                         size_t j = (i < rewrite_cnt) ? i : rewrite_cnt - 1;
 473                         memcpy(&dns_ptr[i], &rewrite[j], sizeof(*rewrite));
 474                 }
 475         }
 476
 477         struct iovec iov = {payload_data, payload_len};
 478         odhcpd_send(iface->dhcpv6_event.uloop.fd, &target, &iov, 1, iface);
 479 }
 480
 481
 482 // Relay client request (regular DHCPv6-relay)
 483 static void relay_client_request(struct sockaddr_in6 *source,
 484                 const void *data, size_t len, struct interface *iface)
 485 {
 486         struct interface *master = odhcpd_get_master_interface();
 487         const struct dhcpv6_relay_header *h = data;
 488         if (!master || master->dhcpv6 != RELAYD_RELAY ||
 489                         h->msg_type == DHCPV6_MSG_RELAY_REPL ||
 490                         h->msg_type == DHCPV6_MSG_RECONFIGURE ||
 491                         h->msg_type == DHCPV6_MSG_REPLY ||
 492                         h->msg_type == DHCPV6_MSG_ADVERTISE)
 493                 return; // Invalid message types for client
 494
 495         syslog(LOG_NOTICE, "Got a DHCPv6-request");
 496
 497         // Construct our forwarding envelope
 498         struct dhcpv6_relay_forward_envelope hdr = {
 499                 .msg_type = DHCPV6_MSG_RELAY_FORW,
 500                 .hop_count = 0,
 501                 .interface_id_type = htons(DHCPV6_OPT_INTERFACE_ID),
 502                 .interface_id_len = htons(sizeof(uint32_t)),
 503                 .relay_message_type = htons(DHCPV6_OPT_RELAY_MSG),
 504                 .relay_message_len = htons(len),
 505         };
 506
 507         if (h->msg_type == DHCPV6_MSG_RELAY_FORW) { // handle relay-forward
 508                 if (h->hop_count >= DHCPV6_HOP_COUNT_LIMIT)
 509                         return; // Invalid hop count
 510                 else
 511                         hdr.hop_count = h->hop_count + 1;
 512         }
 513
 514         // use memcpy here as the destination fields are unaligned
 515         uint32_t ifindex = iface->ifindex;
 516         memcpy(&hdr.peer_address, &source->sin6_addr, sizeof(struct in6_addr));
 517         memcpy(&hdr.interface_id_data, &ifindex, sizeof(ifindex));
 518
 519         // Detect public IP of slave interface to use as link-address
 520         struct odhcpd_ipaddr ip;
 521         if (odhcpd_get_interface_addresses(iface->ifindex, &ip, 1) < 1) {
 522                 // No suitable address! Is the slave not configured yet?
 523                 // Detect public IP of master interface and use it instead
 524                 // This is WRONG and probably violates the RFC. However
 525                 // otherwise we have a hen and egg problem because the
 526                 // slave-interface cannot be auto-configured.
 527                 if (odhcpd_get_interface_addresses(master->ifindex, &ip, 1) < 1)
 528                         return; // Could not obtain a suitable address
 529         }
 530         memcpy(&hdr.link_address, &ip.addr, sizeof(hdr.link_address));
 531
 532         struct sockaddr_in6 dhcpv6_servers = {AF_INET6,
 533                         htons(DHCPV6_SERVER_PORT), 0, ALL_DHCPV6_SERVERS, 0};
 534         struct iovec iov[2] = {{&hdr, sizeof(hdr)}, {(void*)data, len}};
 535         odhcpd_send(iface->dhcpv6_event.uloop.fd, &dhcpv6_servers, iov, 2, master);
 536 }