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 #include <arpa/inet.h>
  22
  23 #include "odhcpd.h"
  24 #include "dhcpv6.h"
  25
  26
  27 static void relay_client_request(struct sockaddr_in6 *source,
  28                 const void *data, size_t len, struct interface *iface);
  29 static void relay_server_response(uint8_t *data, size_t len);
  30
  31 static void handle_dhcpv6(void *addr, void *data, size_t len,
  32                 struct interface *iface, void *dest);
  33 static void handle_client_request(void *addr, void *data, size_t len,
  34                 struct interface *iface, void *dest_addr);
  35
  36
  37
  38 // Create socket and register events
  39 int init_dhcpv6(void)
  40 {
  41         dhcpv6_ia_init();
  42         return 0;
  43 }
  44
  45
  46 int setup_dhcpv6_interface(struct interface *iface, bool enable)
  47 {
  48         if (iface->dhcpv6_event.uloop.fd > 0) {
  49                 uloop_fd_delete(&iface->dhcpv6_event.uloop);
  50                 close(iface->dhcpv6_event.uloop.fd);
  51                 iface->dhcpv6_event.uloop.fd = -1;
  52         }
  53
  54         // Configure multicast settings
  55         if (enable && iface->dhcpv6) {
  56                 int sock = socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  57                 if (sock < 0) {
  58                         syslog(LOG_ERR, "Failed to create DHCPv6 server socket: %s",
  59                                         strerror(errno));
  60                         return -1;
  61                 }
  62
  63                 // Basic IPv6 configuration
  64                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, iface->ifname, strlen(iface->ifname));
  65
  66                 int val = 1;
  67                 setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
  68                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  69                 setsockopt(sock, IPPROTO_IPV6, IPV6_RECVPKTINFO, &val, sizeof(val));
  70
  71                 val = DHCPV6_HOP_COUNT_LIMIT;
  72                 setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &val, sizeof(val));
  73
  74                 val = 0;
  75                 setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &val, sizeof(val));
  76
  77                 struct sockaddr_in6 bind_addr = {AF_INET6, htons(DHCPV6_SERVER_PORT),
  78                                         0, IN6ADDR_ANY_INIT, 0};
  79
  80                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
  81                         syslog(LOG_ERR, "Failed to open DHCPv6 server socket: %s",
  82                                         strerror(errno));
  83                         return -1;
  84                 }
  85
  86                 struct ipv6_mreq relay = {ALL_DHCPV6_RELAYS, iface->ifindex};
  87                 struct ipv6_mreq server = {ALL_DHCPV6_SERVERS, iface->ifindex};
  88                 setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &relay, sizeof(relay));
  89
  90                 if (iface->dhcpv6 == RELAYD_SERVER)
  91                         setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &server, sizeof(server));
  92
  93                 if (iface->dhcpv6 != RELAYD_RELAY || !iface->master)
  94                         ndp_rqs_addr6_dump();
  95
  96                 iface->dhcpv6_event.uloop.fd = sock;
  97                 iface->dhcpv6_event.handle_dgram = handle_dhcpv6;
  98                 odhcpd_register(&iface->dhcpv6_event);
  99         }
 100
 101         return setup_dhcpv6_ia_interface(iface, enable);
 102 }
 103
 104 enum {
 105         IOV_NESTED = 0,
 106         IOV_DEST,
 107         IOV_MAXRT,
 108 #define IOV_STAT IOV_MAXRT
 109         IOV_DNS,
 110         IOV_DNS_ADDR,
 111         IOV_SEARCH,
 112         IOV_SEARCH_DOMAIN,
 113         IOV_PDBUF,
 114 #define IOV_REFRESH IOV_PDBUF
 115         IOV_CERID,
 116         IOV_DHCPV6_RAW,
 117         IOV_RELAY_MSG,
 118         IOV_TOTAL
 119 };
 120
 121 static void handle_nested_message(uint8_t *data, size_t len,
 122                 uint8_t **opts, uint8_t **end, struct iovec iov[IOV_TOTAL - 1])
 123 {
 124         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 125         if (iov[IOV_NESTED].iov_base == NULL) {
 126                 iov[IOV_NESTED].iov_base = data;
 127                 iov[IOV_NESTED].iov_len = len;
 128         }
 129
 130         if (len < sizeof(struct dhcpv6_client_header))
 131                 return;
 132
 133         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW) {
 134                 iov[IOV_NESTED].iov_len = data - (uint8_t*)iov[IOV_NESTED].iov_base;
 135                 struct dhcpv6_client_header *hdr = (void*)data;
 136                 *opts = (uint8_t*)&hdr[1];
 137                 *end = data + len;
 138                 return;
 139         }
 140
 141         uint16_t otype, olen;
 142         uint8_t *odata;
 143         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 144                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 145                         iov[IOV_RELAY_MSG].iov_base = odata + olen;
 146                         iov[IOV_RELAY_MSG].iov_len = (((uint8_t*)iov[IOV_NESTED].iov_base) +
 147                                         iov[IOV_NESTED].iov_len) - (odata + olen);
 148                         handle_nested_message(odata, olen, opts, end, iov);
 149                         return;
 150                 }
 151         }
 152 }
 153
 154
 155 static void update_nested_message(uint8_t *data, size_t len, ssize_t pdiff)
 156 {
 157         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 158         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW)
 159                 return;
 160
 161         hdr->msg_type = DHCPV6_MSG_RELAY_REPL;
 162
 163         uint16_t otype, olen;
 164         uint8_t *odata;
 165         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 166                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 167                         olen += pdiff;
 168                         odata[-2] = (olen >> 8) & 0xff;
 169                         odata[-1] = olen & 0xff;
 170                         update_nested_message(odata, olen - pdiff, pdiff);
 171                         return;
 172                 }
 173         }
 174 }
 175
 176 // Simple DHCPv6-server for information requests
 177 static void handle_client_request(void *addr, void *data, size_t len,
 178                 struct interface *iface, void *dest_addr)
 179 {
 180         struct dhcpv6_client_header *hdr = data;
 181
 182         if (len < sizeof(*hdr))
 183                 return;
 184
 185         syslog(LOG_NOTICE, "Got DHCPv6 request");
 186
 187         // Construct reply message
 188         struct __attribute__((packed)) {
 189                 uint8_t msg_type;
 190                 uint8_t tr_id[3];
 191                 uint16_t serverid_type;
 192                 uint16_t serverid_length;
 193                 uint16_t duid_type;
 194                 uint16_t hardware_type;
 195                 uint8_t mac[6];
 196                 uint16_t clientid_type;
 197                 uint16_t clientid_length;
 198                 uint8_t clientid_buf[130];
 199         } dest = {
 200                 .msg_type = DHCPV6_MSG_REPLY,
 201                 .serverid_type = htons(DHCPV6_OPT_SERVERID),
 202                 .serverid_length = htons(10),
 203                 .duid_type = htons(3),
 204                 .hardware_type = htons(1),
 205                 .clientid_type = htons(DHCPV6_OPT_CLIENTID),
 206                 .clientid_buf = {0}
 207         };
 208         odhcpd_get_mac(iface, dest.mac);
 209
 210         struct __attribute__((packed)) {
 211                 uint16_t type;
 212                 uint16_t len;
 213                 uint32_t value;
 214         } maxrt = {htons(DHCPV6_OPT_SOL_MAX_RT), htons(sizeof(maxrt) - 4),
 215                         htonl(60)};
 216
 217         struct __attribute__((packed)) {
 218                 uint16_t type;
 219                 uint16_t len;
 220                 uint16_t value;
 221         } stat = {htons(DHCPV6_OPT_STATUS), htons(sizeof(stat) - 4),
 222                         htons(DHCPV6_STATUS_USEMULTICAST)};
 223
 224         struct __attribute__((packed)) {
 225                 uint16_t type;
 226                 uint16_t len;
 227                 uint32_t value;
 228         } refresh = {htons(DHCPV6_OPT_INFO_REFRESH), htons(sizeof(uint32_t)),
 229                         htonl(600)};
 230
 231         struct in6_addr dns_addr, *dns_addr_ptr = iface->dns;
 232         size_t dns_cnt = iface->dns_cnt;
 233
 234         if ((dns_cnt == 0) &&
 235                 !odhcpd_get_interface_dns_addr(iface, &dns_addr)) {
 236                 dns_addr_ptr = &dns_addr;
 237                 dns_cnt = 1;
 238         }
 239
 240         struct {
 241                 uint16_t type;
 242                 uint16_t len;
 243         } dns = {htons(DHCPV6_OPT_DNS_SERVERS), htons(dns_cnt * sizeof(*dns_addr_ptr))};
 244
 245
 246
 247         // DNS Search options
 248         uint8_t search_buf[256], *search_domain = iface->search;
 249         size_t search_len = iface->search_len;
 250
 251         if (!search_domain && !res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 252                 int len = dn_comp(_res.dnsrch[0], search_buf,
 253                                 sizeof(search_buf), NULL, NULL);
 254                 if (len > 0) {
 255                         search_domain = search_buf;
 256                         search_len = len;
 257                 }
 258         }
 259
 260         struct {
 261                 uint16_t type;
 262                 uint16_t len;
 263         } search = {htons(DHCPV6_OPT_DNS_DOMAIN), htons(search_len)};
 264
 265
 266         struct dhcpv6_cer_id cerid = {
 267 #ifdef EXT_CER_ID
 268                 .type = htons(EXT_CER_ID),
 269 #endif
 270                 .len = htons(36),
 271                 .addr = iface->dhcpv6_pd_cer,
 272         };
 273
 274
 275         uint8_t pdbuf[512];
 276         struct iovec iov[IOV_TOTAL] = {
 277                 [IOV_NESTED] = {NULL, 0},
 278                 [IOV_DEST] = {&dest, (uint8_t*)&dest.clientid_type - (uint8_t*)&dest},
 279                 [IOV_MAXRT] = {&maxrt, sizeof(maxrt)},
 280                 [IOV_DNS] = {&dns, (dns_cnt) ? sizeof(dns) : 0},
 281                 [IOV_DNS_ADDR] = {dns_addr_ptr, dns_cnt * sizeof(*dns_addr_ptr)},
 282                 [IOV_SEARCH] = {&search, (search_len) ? sizeof(search) : 0},
 283                 [IOV_SEARCH_DOMAIN] = {search_domain, search_len},
 284                 [IOV_PDBUF] = {pdbuf, 0},
 285                 [IOV_CERID] = {&cerid, 0},
 286                 [IOV_DHCPV6_RAW] = {iface->dhcpv6_raw, iface->dhcpv6_raw_len},
 287                 [IOV_RELAY_MSG] = {NULL, 0}
 288         };
 289
 290         uint8_t *opts = (uint8_t*)&hdr[1], *opts_end = (uint8_t*)data + len;
 291         if (hdr->msg_type == DHCPV6_MSG_RELAY_FORW)
 292                 handle_nested_message(data, len, &opts, &opts_end, iov);
 293
 294         memcpy(dest.tr_id, &opts[-3], sizeof(dest.tr_id));
 295
 296         if (opts[-4] == DHCPV6_MSG_ADVERTISE || opts[-4] == DHCPV6_MSG_REPLY || opts[-4] == DHCPV6_MSG_RELAY_REPL)
 297                 return;
 298
 299         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 300                 (opts[-4] == DHCPV6_MSG_SOLICIT || opts[-4] == DHCPV6_MSG_CONFIRM ||
 301                  opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST))
 302                 return;
 303
 304         if (opts[-4] == DHCPV6_MSG_SOLICIT) {
 305                 dest.msg_type = DHCPV6_MSG_ADVERTISE;
 306         } else if (opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST) {
 307                 iov[IOV_REFRESH].iov_base = &refresh;
 308                 iov[IOV_REFRESH].iov_len = sizeof(refresh);
 309
 310                 // Return inf max rt option in reply to information request
 311                 maxrt.type = htons(DHCPV6_OPT_INF_MAX_RT);
 312         }
 313
 314         // Go through options and find what we need
 315         uint16_t otype, olen;
 316         uint8_t *odata;
 317         dhcpv6_for_each_option(opts, opts_end, otype, olen, odata) {
 318                 if (otype == DHCPV6_OPT_CLIENTID && olen <= 130) {
 319                         dest.clientid_length = htons(olen);
 320                         memcpy(dest.clientid_buf, odata, olen);
 321                         iov[IOV_DEST].iov_len += 4 + olen;
 322                 } else if (otype == DHCPV6_OPT_SERVERID) {
 323                         if (olen != ntohs(dest.serverid_length) ||
 324                                         memcmp(odata, &dest.duid_type, olen))
 325                                 return; // Not for us
 326                 } else if (iface->filter_class && otype == DHCPV6_OPT_USER_CLASS) {
 327                         uint8_t *c = odata, *cend = &odata[olen];
 328                         for (; &c[2] <= cend && &c[2 + (c[0] << 8) + c[1]] <= cend; c = &c[2 + (c[0] << 8) + c[1]]) {
 329                                 size_t elen = strlen(iface->filter_class);
 330                                 if (((((size_t)c[0]) << 8) | c[1]) == elen && !memcmp(&c[2], iface->filter_class, elen))
 331                                         return; // Ignore from homenet
 332                         }
 333                 } else if (otype == DHCPV6_OPT_IA_PD) {
 334 #ifdef EXT_CER_ID
 335                         iov[IOV_CERID].iov_len = sizeof(cerid);
 336
 337                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)) {
 338                                 struct odhcpd_ipaddr addrs[32];
 339                                 ssize_t len = odhcpd_get_interface_addresses(0, addrs,
 340                                                 ARRAY_SIZE(addrs));
 341
 342                                 for (ssize_t i = 0; i < len; ++i)
 343                                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)
 344                                                         || memcmp(&addrs[i].addr, &cerid.addr, sizeof(cerid.addr)) < 0)
 345                                                 cerid.addr = addrs[i].addr;
 346                         }
 347 #endif
 348                 }
 349         }
 350
 351         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 352                 (opts[-4] == DHCPV6_MSG_REQUEST || opts[-4] == DHCPV6_MSG_RENEW ||
 353                  opts[-4] == DHCPV6_MSG_RELEASE || opts[-4] == DHCPV6_MSG_DECLINE)) {
 354                 iov[IOV_STAT].iov_base = &stat;
 355                 iov[IOV_STAT].iov_len = sizeof(stat);
 356
 357                 for (ssize_t i = IOV_STAT + 1; i < IOV_TOTAL; ++i)
 358                         iov[i].iov_len = 0;
 359
 360                 odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 361                 return;
 362         }
 363
 364         if (opts[-4] != DHCPV6_MSG_INFORMATION_REQUEST) {
 365                 ssize_t ialen = dhcpv6_handle_ia(pdbuf, sizeof(pdbuf), iface, addr, &opts[-4], opts_end);
 366                 iov[IOV_PDBUF].iov_len = ialen;
 367                 if (ialen < 0 || (ialen == 0 && (opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_CONFIRM)))
 368                         return;
 369         }
 370
 371         if (iov[IOV_NESTED].iov_len > 0) // Update length
 372                 update_nested_message(data, len, iov[IOV_DEST].iov_len + iov[IOV_MAXRT].iov_len +
 373                                 iov[IOV_DNS].iov_len + iov[IOV_DNS_ADDR].iov_len +
 374                                 iov[IOV_SEARCH].iov_len + iov[IOV_SEARCH_DOMAIN].iov_len +
 375                                 iov[IOV_PDBUF].iov_len + iov[IOV_CERID].iov_len +
 376                                 iov[IOV_DHCPV6_RAW].iov_len - (4 + opts_end - opts));
 377
 378         odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 379 }
 380
 381
 382 // Central DHCPv6-relay handler
 383 static void handle_dhcpv6(void *addr, void *data, size_t len,
 384                 struct interface *iface, void *dest_addr)
 385 {
 386         if (iface->dhcpv6 == RELAYD_SERVER) {
 387                 handle_client_request(addr, data, len, iface, dest_addr);
 388         } else if (iface->dhcpv6 == RELAYD_RELAY) {
 389                 if (iface->master)
 390                         relay_server_response(data, len);
 391                 else
 392                         relay_client_request(addr, data, len, iface);
 393         }
 394 }
 395
 396
 397 // Relay server response (regular relay server handling)
 398 static void relay_server_response(uint8_t *data, size_t len)
 399 {
 400         // Information we need to gather
 401         uint8_t *payload_data = NULL;
 402         size_t payload_len = 0;
 403         int32_t ifaceidx = 0;
 404         struct sockaddr_in6 target = {AF_INET6, htons(DHCPV6_CLIENT_PORT),
 405                 0, IN6ADDR_ANY_INIT, 0};
 406
 407         syslog(LOG_NOTICE, "Got a DHCPv6-reply");
 408
 409         int otype, olen;
 410         uint8_t *odata, *end = data + len;
 411
 412         // Relay DHCPv6 reply from server to client
 413         struct dhcpv6_relay_header *h = (void*)data;
 414         if (len < sizeof(*h) || h->msg_type != DHCPV6_MSG_RELAY_REPL)
 415                 return;
 416
 417         memcpy(&target.sin6_addr, &h->peer_address,
 418                         sizeof(struct in6_addr));
 419
 420         // Go through options and find what we need
 421         dhcpv6_for_each_option(h->options, end, otype, olen, odata) {
 422                 if (otype == DHCPV6_OPT_INTERFACE_ID
 423                                 && olen == sizeof(ifaceidx)) {
 424                         memcpy(&ifaceidx, odata, sizeof(ifaceidx));
 425                 } else if (otype == DHCPV6_OPT_RELAY_MSG) {
 426                         payload_data = odata;
 427                         payload_len = olen;
 428                 }
 429         }
 430
 431         // Invalid interface-id or basic payload
 432         struct interface *iface = odhcpd_get_interface_by_index(ifaceidx);
 433         if (!iface || iface->master || !payload_data || payload_len < 4)
 434                 return;
 435
 436         bool is_authenticated = false;
 437         struct in6_addr *dns_ptr = NULL;
 438         size_t dns_count = 0;
 439
 440         // If the payload is relay-reply we have to send to the server port
 441         if (payload_data[0] == DHCPV6_MSG_RELAY_REPL) {
 442                 target.sin6_port = htons(DHCPV6_SERVER_PORT);
 443         } else { // Go through the payload data
 444                 struct dhcpv6_client_header *h = (void*)payload_data;
 445                 end = payload_data + payload_len;
 446
 447                 dhcpv6_for_each_option(&h[1], end, otype, olen, odata) {
 448                         if (otype == DHCPV6_OPT_DNS_SERVERS && olen >= 16) {
 449                                 dns_ptr = (struct in6_addr*)odata;
 450                                 dns_count = olen / 16;
 451                         } else if (otype == DHCPV6_OPT_AUTH) {
 452                                 is_authenticated = true;
 453                         }
 454                 }
 455         }
 456
 457         // Rewrite DNS servers if requested
 458         if (iface->always_rewrite_dns && dns_ptr && dns_count > 0) {
 459                 if (is_authenticated)
 460                         return; // Impossible to rewrite
 461
 462                 const struct in6_addr *rewrite = iface->dns;
 463                 struct in6_addr addr;
 464                 size_t rewrite_cnt = iface->dns_cnt;
 465
 466                 if (rewrite_cnt == 0) {
 467                         if (odhcpd_get_interface_dns_addr(iface, &addr))
 468                                 return; // Unable to get interface address
 469
 470                         rewrite = &addr;
 471                         rewrite_cnt = 1;
 472                 }
 473
 474                 // Copy over any other addresses
 475                 for (size_t i = 0; i < dns_count; ++i) {
 476                         size_t j = (i < rewrite_cnt) ? i : rewrite_cnt - 1;
 477                         memcpy(&dns_ptr[i], &rewrite[j], sizeof(*rewrite));
 478                 }
 479         }
 480
 481         struct iovec iov = {payload_data, payload_len};
 482         odhcpd_send(iface->dhcpv6_event.uloop.fd, &target, &iov, 1, iface);
 483 }
 484
 485
 486 // Relay client request (regular DHCPv6-relay)
 487 static void relay_client_request(struct sockaddr_in6 *source,
 488                 const void *data, size_t len, struct interface *iface)
 489 {
 490         struct interface *master = odhcpd_get_master_interface();
 491         const struct dhcpv6_relay_header *h = data;
 492         if (!master || master->dhcpv6 != RELAYD_RELAY ||
 493                         h->msg_type == DHCPV6_MSG_RELAY_REPL ||
 494                         h->msg_type == DHCPV6_MSG_RECONFIGURE ||
 495                         h->msg_type == DHCPV6_MSG_REPLY ||
 496                         h->msg_type == DHCPV6_MSG_ADVERTISE)
 497                 return; // Invalid message types for client
 498
 499         syslog(LOG_NOTICE, "Got a DHCPv6-request");
 500
 501         // Construct our forwarding envelope
 502         struct dhcpv6_relay_forward_envelope hdr = {
 503                 .msg_type = DHCPV6_MSG_RELAY_FORW,
 504                 .hop_count = 0,
 505                 .interface_id_type = htons(DHCPV6_OPT_INTERFACE_ID),
 506                 .interface_id_len = htons(sizeof(uint32_t)),
 507                 .relay_message_type = htons(DHCPV6_OPT_RELAY_MSG),
 508                 .relay_message_len = htons(len),
 509         };
 510
 511         if (h->msg_type == DHCPV6_MSG_RELAY_FORW) { // handle relay-forward
 512                 if (h->hop_count >= DHCPV6_HOP_COUNT_LIMIT)
 513                         return; // Invalid hop count
 514                 else
 515                         hdr.hop_count = h->hop_count + 1;
 516         }
 517
 518         // use memcpy here as the destination fields are unaligned
 519         uint32_t ifindex = iface->ifindex;
 520         memcpy(&hdr.peer_address, &source->sin6_addr, sizeof(struct in6_addr));
 521         memcpy(&hdr.interface_id_data, &ifindex, sizeof(ifindex));
 522
 523         // Detect public IP of slave interface to use as link-address
 524         struct odhcpd_ipaddr ip;
 525         if (odhcpd_get_interface_addresses(iface->ifindex, &ip, 1) < 1) {
 526                 // No suitable address! Is the slave not configured yet?
 527                 // Detect public IP of master interface and use it instead
 528                 // This is WRONG and probably violates the RFC. However
 529                 // otherwise we have a hen and egg problem because the
 530                 // slave-interface cannot be auto-configured.
 531                 if (odhcpd_get_interface_addresses(master->ifindex, &ip, 1) < 1)
 532                         return; // Could not obtain a suitable address
 533         }
 534         memcpy(&hdr.link_address, &ip.addr, sizeof(hdr.link_address));
 535
 536         struct sockaddr_in6 dhcpv6_servers = {AF_INET6,
 537                         htons(DHCPV6_SERVER_PORT), 0, ALL_DHCPV6_SERVERS, 0};
 538         struct iovec iov[2] = {{&hdr, sizeof(hdr)}, {(void*)data, len}};
 539         odhcpd_send(master->dhcpv6_event.uloop.fd, &dhcpv6_servers, iov, 2, master);
 540 }