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 == MODE_SERVER)
  91                         setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &server, sizeof(server));
  92
  93                 iface->dhcpv6_event.uloop.fd = sock;
  94                 iface->dhcpv6_event.handle_dgram = handle_dhcpv6;
  95                 odhcpd_register(&iface->dhcpv6_event);
  96         }
  97
  98         return setup_dhcpv6_ia_interface(iface, enable);
  99 }
 100
 101 enum {
 102         IOV_NESTED = 0,
 103         IOV_DEST,
 104         IOV_MAXRT,
 105 #define IOV_STAT IOV_MAXRT
 106         IOV_DNS,
 107         IOV_DNS_ADDR,
 108         IOV_SEARCH,
 109         IOV_SEARCH_DOMAIN,
 110         IOV_PDBUF,
 111 #define IOV_REFRESH IOV_PDBUF
 112         IOV_CERID,
 113         IOV_DHCPV6_RAW,
 114         IOV_RELAY_MSG,
 115         IOV_TOTAL
 116 };
 117
 118 static void handle_nested_message(uint8_t *data, size_t len,
 119                 uint8_t **opts, uint8_t **end, struct iovec iov[IOV_TOTAL - 1])
 120 {
 121         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 122         if (iov[IOV_NESTED].iov_base == NULL) {
 123                 iov[IOV_NESTED].iov_base = data;
 124                 iov[IOV_NESTED].iov_len = len;
 125         }
 126
 127         if (len < sizeof(struct dhcpv6_client_header))
 128                 return;
 129
 130         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW) {
 131                 iov[IOV_NESTED].iov_len = data - (uint8_t*)iov[IOV_NESTED].iov_base;
 132                 struct dhcpv6_client_header *hdr = (void*)data;
 133                 *opts = (uint8_t*)&hdr[1];
 134                 *end = data + len;
 135                 return;
 136         }
 137
 138         uint16_t otype, olen;
 139         uint8_t *odata;
 140         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 141                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 142                         iov[IOV_RELAY_MSG].iov_base = odata + olen;
 143                         iov[IOV_RELAY_MSG].iov_len = (((uint8_t*)iov[IOV_NESTED].iov_base) +
 144                                         iov[IOV_NESTED].iov_len) - (odata + olen);
 145                         handle_nested_message(odata, olen, opts, end, iov);
 146                         return;
 147                 }
 148         }
 149 }
 150
 151
 152 static void update_nested_message(uint8_t *data, size_t len, ssize_t pdiff)
 153 {
 154         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 155         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW)
 156                 return;
 157
 158         hdr->msg_type = DHCPV6_MSG_RELAY_REPL;
 159
 160         uint16_t otype, olen;
 161         uint8_t *odata;
 162         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 163                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 164                         olen += pdiff;
 165                         odata[-2] = (olen >> 8) & 0xff;
 166                         odata[-1] = olen & 0xff;
 167                         update_nested_message(odata, olen - pdiff, pdiff);
 168                         return;
 169                 }
 170         }
 171 }
 172
 173 // Simple DHCPv6-server for information requests
 174 static void handle_client_request(void *addr, void *data, size_t len,
 175                 struct interface *iface, void *dest_addr)
 176 {
 177         struct dhcpv6_client_header *hdr = data;
 178
 179         if (len < sizeof(*hdr))
 180                 return;
 181
 182         syslog(LOG_NOTICE, "Got DHCPv6 request");
 183
 184         // Construct reply message
 185         struct __attribute__((packed)) {
 186                 uint8_t msg_type;
 187                 uint8_t tr_id[3];
 188                 uint16_t serverid_type;
 189                 uint16_t serverid_length;
 190                 uint16_t duid_type;
 191                 uint16_t hardware_type;
 192                 uint8_t mac[6];
 193                 uint16_t clientid_type;
 194                 uint16_t clientid_length;
 195                 uint8_t clientid_buf[130];
 196         } dest = {
 197                 .msg_type = DHCPV6_MSG_REPLY,
 198                 .serverid_type = htons(DHCPV6_OPT_SERVERID),
 199                 .serverid_length = htons(10),
 200                 .duid_type = htons(3),
 201                 .hardware_type = htons(1),
 202                 .clientid_type = htons(DHCPV6_OPT_CLIENTID),
 203                 .clientid_buf = {0}
 204         };
 205         odhcpd_get_mac(iface, dest.mac);
 206
 207         struct __attribute__((packed)) {
 208                 uint16_t type;
 209                 uint16_t len;
 210                 uint32_t value;
 211         } maxrt = {htons(DHCPV6_OPT_SOL_MAX_RT), htons(sizeof(maxrt) - 4),
 212                         htonl(60)};
 213
 214         struct __attribute__((packed)) {
 215                 uint16_t type;
 216                 uint16_t len;
 217                 uint16_t value;
 218         } stat = {htons(DHCPV6_OPT_STATUS), htons(sizeof(stat) - 4),
 219                         htons(DHCPV6_STATUS_USEMULTICAST)};
 220
 221         struct __attribute__((packed)) {
 222                 uint16_t type;
 223                 uint16_t len;
 224                 uint32_t value;
 225         } refresh = {htons(DHCPV6_OPT_INFO_REFRESH), htons(sizeof(uint32_t)),
 226                         htonl(600)};
 227
 228         struct in6_addr dns_addr, *dns_addr_ptr = iface->dns;
 229         size_t dns_cnt = iface->dns_cnt;
 230
 231         if ((dns_cnt == 0) &&
 232                 !odhcpd_get_interface_dns_addr(iface, &dns_addr)) {
 233                 dns_addr_ptr = &dns_addr;
 234                 dns_cnt = 1;
 235         }
 236
 237         struct {
 238                 uint16_t type;
 239                 uint16_t len;
 240         } dns = {htons(DHCPV6_OPT_DNS_SERVERS), htons(dns_cnt * sizeof(*dns_addr_ptr))};
 241
 242
 243
 244         // DNS Search options
 245         uint8_t search_buf[256], *search_domain = iface->search;
 246         size_t search_len = iface->search_len;
 247
 248         if (!search_domain && !res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 249                 int len = dn_comp(_res.dnsrch[0], search_buf,
 250                                 sizeof(search_buf), NULL, NULL);
 251                 if (len > 0) {
 252                         search_domain = search_buf;
 253                         search_len = len;
 254                 }
 255         }
 256
 257         struct {
 258                 uint16_t type;
 259                 uint16_t len;
 260         } search = {htons(DHCPV6_OPT_DNS_DOMAIN), htons(search_len)};
 261
 262
 263         struct dhcpv6_cer_id cerid = {
 264 #ifdef EXT_CER_ID
 265                 .type = htons(EXT_CER_ID),
 266 #endif
 267                 .len = htons(36),
 268                 .addr = iface->dhcpv6_pd_cer,
 269         };
 270
 271
 272         uint8_t pdbuf[512];
 273         struct iovec iov[IOV_TOTAL] = {
 274                 [IOV_NESTED] = {NULL, 0},
 275                 [IOV_DEST] = {&dest, (uint8_t*)&dest.clientid_type - (uint8_t*)&dest},
 276                 [IOV_MAXRT] = {&maxrt, sizeof(maxrt)},
 277                 [IOV_DNS] = {&dns, (dns_cnt) ? sizeof(dns) : 0},
 278                 [IOV_DNS_ADDR] = {dns_addr_ptr, dns_cnt * sizeof(*dns_addr_ptr)},
 279                 [IOV_SEARCH] = {&search, (search_len) ? sizeof(search) : 0},
 280                 [IOV_SEARCH_DOMAIN] = {search_domain, search_len},
 281                 [IOV_PDBUF] = {pdbuf, 0},
 282                 [IOV_CERID] = {&cerid, 0},
 283                 [IOV_DHCPV6_RAW] = {iface->dhcpv6_raw, iface->dhcpv6_raw_len},
 284                 [IOV_RELAY_MSG] = {NULL, 0}
 285         };
 286
 287         uint8_t *opts = (uint8_t*)&hdr[1], *opts_end = (uint8_t*)data + len;
 288         if (hdr->msg_type == DHCPV6_MSG_RELAY_FORW)
 289                 handle_nested_message(data, len, &opts, &opts_end, iov);
 290
 291         memcpy(dest.tr_id, &opts[-3], sizeof(dest.tr_id));
 292
 293         if (opts[-4] == DHCPV6_MSG_ADVERTISE || opts[-4] == DHCPV6_MSG_REPLY || opts[-4] == DHCPV6_MSG_RELAY_REPL)
 294                 return;
 295
 296         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 297                 (opts[-4] == DHCPV6_MSG_SOLICIT || opts[-4] == DHCPV6_MSG_CONFIRM ||
 298                  opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST))
 299                 return;
 300
 301         if (opts[-4] == DHCPV6_MSG_SOLICIT) {
 302                 dest.msg_type = DHCPV6_MSG_ADVERTISE;
 303         } else if (opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST) {
 304                 iov[IOV_REFRESH].iov_base = &refresh;
 305                 iov[IOV_REFRESH].iov_len = sizeof(refresh);
 306
 307                 // Return inf max rt option in reply to information request
 308                 maxrt.type = htons(DHCPV6_OPT_INF_MAX_RT);
 309         }
 310
 311         // Go through options and find what we need
 312         uint16_t otype, olen;
 313         uint8_t *odata;
 314         dhcpv6_for_each_option(opts, opts_end, otype, olen, odata) {
 315                 if (otype == DHCPV6_OPT_CLIENTID && olen <= 130) {
 316                         dest.clientid_length = htons(olen);
 317                         memcpy(dest.clientid_buf, odata, olen);
 318                         iov[IOV_DEST].iov_len += 4 + olen;
 319                 } else if (otype == DHCPV6_OPT_SERVERID) {
 320                         if (olen != ntohs(dest.serverid_length) ||
 321                                         memcmp(odata, &dest.duid_type, olen))
 322                                 return; // Not for us
 323                 } else if (iface->filter_class && otype == DHCPV6_OPT_USER_CLASS) {
 324                         uint8_t *c = odata, *cend = &odata[olen];
 325                         for (; &c[2] <= cend && &c[2 + (c[0] << 8) + c[1]] <= cend; c = &c[2 + (c[0] << 8) + c[1]]) {
 326                                 size_t elen = strlen(iface->filter_class);
 327                                 if (((((size_t)c[0]) << 8) | c[1]) == elen && !memcmp(&c[2], iface->filter_class, elen))
 328                                         return; // Ignore from homenet
 329                         }
 330                 } else if (otype == DHCPV6_OPT_IA_PD) {
 331 #ifdef EXT_CER_ID
 332                         iov[IOV_CERID].iov_len = sizeof(cerid);
 333
 334                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)) {
 335                                 struct odhcpd_ipaddr *addrs;
 336                                 ssize_t len = odhcpd_get_interface_addresses(0, true, &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                                 free(addrs);
 344                         }
 345 #endif
 346                 }
 347         }
 348
 349         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 350                 (opts[-4] == DHCPV6_MSG_REQUEST || opts[-4] == DHCPV6_MSG_RENEW ||
 351                  opts[-4] == DHCPV6_MSG_RELEASE || opts[-4] == DHCPV6_MSG_DECLINE)) {
 352                 iov[IOV_STAT].iov_base = &stat;
 353                 iov[IOV_STAT].iov_len = sizeof(stat);
 354
 355                 for (ssize_t i = IOV_STAT + 1; i < IOV_TOTAL; ++i)
 356                         iov[i].iov_len = 0;
 357
 358                 odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 359                 return;
 360         }
 361
 362         if (opts[-4] != DHCPV6_MSG_INFORMATION_REQUEST) {
 363                 ssize_t ialen = dhcpv6_handle_ia(pdbuf, sizeof(pdbuf), iface, addr, &opts[-4], opts_end);
 364                 iov[IOV_PDBUF].iov_len = ialen;
 365                 if (ialen < 0 || (ialen == 0 && (opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_CONFIRM)))
 366                         return;
 367         }
 368
 369         if (iov[IOV_NESTED].iov_len > 0) // Update length
 370                 update_nested_message(data, len, iov[IOV_DEST].iov_len + iov[IOV_MAXRT].iov_len +
 371                                 iov[IOV_DNS].iov_len + iov[IOV_DNS_ADDR].iov_len +
 372                                 iov[IOV_SEARCH].iov_len + iov[IOV_SEARCH_DOMAIN].iov_len +
 373                                 iov[IOV_PDBUF].iov_len + iov[IOV_CERID].iov_len +
 374                                 iov[IOV_DHCPV6_RAW].iov_len - (4 + opts_end - opts));
 375
 376         odhcpd_send(iface->dhcpv6_event.uloop.fd, addr, iov, ARRAY_SIZE(iov), iface);
 377 }
 378
 379
 380 // Central DHCPv6-relay handler
 381 static void handle_dhcpv6(void *addr, void *data, size_t len,
 382                 struct interface *iface, void *dest_addr)
 383 {
 384         if (iface->dhcpv6 == MODE_SERVER) {
 385                 handle_client_request(addr, data, len, iface, dest_addr);
 386         } else if (iface->dhcpv6 == MODE_RELAY) {
 387                 if (iface->master)
 388                         relay_server_response(data, len);
 389                 else
 390                         relay_client_request(addr, data, len, iface);
 391         }
 392 }
 393
 394
 395 // Relay server response (regular relay server handling)
 396 static void relay_server_response(uint8_t *data, size_t len)
 397 {
 398         // Information we need to gather
 399         uint8_t *payload_data = NULL;
 400         size_t payload_len = 0;
 401         int32_t ifaceidx = 0;
 402         struct sockaddr_in6 target = {AF_INET6, htons(DHCPV6_CLIENT_PORT),
 403                 0, IN6ADDR_ANY_INIT, 0};
 404
 405         syslog(LOG_NOTICE, "Got a DHCPv6-reply");
 406
 407         int otype, olen;
 408         uint8_t *odata, *end = data + len;
 409
 410         // Relay DHCPv6 reply from server to client
 411         struct dhcpv6_relay_header *h = (void*)data;
 412         if (len < sizeof(*h) || h->msg_type != DHCPV6_MSG_RELAY_REPL)
 413                 return;
 414
 415         memcpy(&target.sin6_addr, &h->peer_address,
 416                         sizeof(struct in6_addr));
 417
 418         // Go through options and find what we need
 419         dhcpv6_for_each_option(h->options, end, otype, olen, odata) {
 420                 if (otype == DHCPV6_OPT_INTERFACE_ID
 421                                 && olen == sizeof(ifaceidx)) {
 422                         memcpy(&ifaceidx, odata, sizeof(ifaceidx));
 423                 } else if (otype == DHCPV6_OPT_RELAY_MSG) {
 424                         payload_data = odata;
 425                         payload_len = olen;
 426                 }
 427         }
 428
 429         // Invalid interface-id or basic payload
 430         struct interface *iface = odhcpd_get_interface_by_index(ifaceidx);
 431         if (!iface || iface->master || !payload_data || payload_len < 4)
 432                 return;
 433
 434         bool is_authenticated = false;
 435         struct in6_addr *dns_ptr = NULL;
 436         size_t dns_count = 0;
 437
 438         // If the payload is relay-reply we have to send to the server port
 439         if (payload_data[0] == DHCPV6_MSG_RELAY_REPL) {
 440                 target.sin6_port = htons(DHCPV6_SERVER_PORT);
 441         } else { // Go through the payload data
 442                 struct dhcpv6_client_header *h = (void*)payload_data;
 443                 end = payload_data + payload_len;
 444
 445                 dhcpv6_for_each_option(&h[1], end, otype, olen, odata) {
 446                         if (otype == DHCPV6_OPT_DNS_SERVERS && olen >= 16) {
 447                                 dns_ptr = (struct in6_addr*)odata;
 448                                 dns_count = olen / 16;
 449                         } else if (otype == DHCPV6_OPT_AUTH) {
 450                                 is_authenticated = true;
 451                         }
 452                 }
 453         }
 454
 455         // Rewrite DNS servers if requested
 456         if (iface->always_rewrite_dns && dns_ptr && dns_count > 0) {
 457                 if (is_authenticated)
 458                         return; // Impossible to rewrite
 459
 460                 const struct in6_addr *rewrite = iface->dns;
 461                 struct in6_addr addr;
 462                 size_t rewrite_cnt = iface->dns_cnt;
 463
 464                 if (rewrite_cnt == 0) {
 465                         if (odhcpd_get_interface_dns_addr(iface, &addr))
 466                                 return; // Unable to get interface address
 467
 468                         rewrite = &addr;
 469                         rewrite_cnt = 1;
 470                 }
 471
 472                 // Copy over any other addresses
 473                 for (size_t i = 0; i < dns_count; ++i) {
 474                         size_t j = (i < rewrite_cnt) ? i : rewrite_cnt - 1;
 475                         memcpy(&dns_ptr[i], &rewrite[j], sizeof(*rewrite));
 476                 }
 477         }
 478
 479         struct iovec iov = {payload_data, payload_len};
 480         odhcpd_send(iface->dhcpv6_event.uloop.fd, &target, &iov, 1, iface);
 481 }
 482
 483 static struct odhcpd_ipaddr *relay_link_address(struct interface *iface)
 484 {
 485         struct odhcpd_ipaddr *addr = NULL;
 486         time_t now = odhcpd_time();
 487
 488         for (size_t i = 0; i < iface->ia_addr_len; i++) {
 489                 if (iface->ia_addr[i].valid <= (uint32_t)now)
 490                         continue;
 491
 492                 if (iface->ia_addr[i].preferred > (uint32_t)now) {
 493                         addr = &iface->ia_addr[i];
 494                         break;
 495                 }
 496
 497                 if (!addr || (iface->ia_addr[i].valid > addr->valid))
 498                         addr = &iface->ia_addr[i];
 499         }
 500
 501         return addr;
 502 }
 503
 504 // Relay client request (regular DHCPv6-relay)
 505 static void relay_client_request(struct sockaddr_in6 *source,
 506                 const void *data, size_t len, struct interface *iface)
 507 {
 508         struct interface *master = odhcpd_get_master_interface();
 509         const struct dhcpv6_relay_header *h = data;
 510         if (!master || master->dhcpv6 != MODE_RELAY ||
 511                         h->msg_type == DHCPV6_MSG_RELAY_REPL ||
 512                         h->msg_type == DHCPV6_MSG_RECONFIGURE ||
 513                         h->msg_type == DHCPV6_MSG_REPLY ||
 514                         h->msg_type == DHCPV6_MSG_ADVERTISE)
 515                 return; // Invalid message types for client
 516
 517         syslog(LOG_NOTICE, "Got a DHCPv6-request");
 518
 519         // Construct our forwarding envelope
 520         struct dhcpv6_relay_forward_envelope hdr = {
 521                 .msg_type = DHCPV6_MSG_RELAY_FORW,
 522                 .hop_count = 0,
 523                 .interface_id_type = htons(DHCPV6_OPT_INTERFACE_ID),
 524                 .interface_id_len = htons(sizeof(uint32_t)),
 525                 .relay_message_type = htons(DHCPV6_OPT_RELAY_MSG),
 526                 .relay_message_len = htons(len),
 527         };
 528
 529         if (h->msg_type == DHCPV6_MSG_RELAY_FORW) { // handle relay-forward
 530                 if (h->hop_count >= DHCPV6_HOP_COUNT_LIMIT)
 531                         return; // Invalid hop count
 532                 else
 533                         hdr.hop_count = h->hop_count + 1;
 534         }
 535
 536         // use memcpy here as the destination fields are unaligned
 537         uint32_t ifindex = iface->ifindex;
 538         memcpy(&hdr.peer_address, &source->sin6_addr, sizeof(struct in6_addr));
 539         memcpy(&hdr.interface_id_data, &ifindex, sizeof(ifindex));
 540
 541         // Detect public IP of slave interface to use as link-address
 542         struct odhcpd_ipaddr *ip = relay_link_address(iface);
 543         if (!ip) {
 544                 // No suitable address! Is the slave not configured yet?
 545                 // Detect public IP of master interface and use it instead
 546                 // This is WRONG and probably violates the RFC. However
 547                 // otherwise we have a hen and egg problem because the
 548                 // slave-interface cannot be auto-configured.
 549                 ip = relay_link_address(master);
 550                 if (!ip)
 551                         return; // Could not obtain a suitable address
 552         }
 553
 554         memcpy(&hdr.link_address, &ip->addr.in6, sizeof(hdr.link_address));
 555
 556         struct sockaddr_in6 dhcpv6_servers = {AF_INET6,
 557                         htons(DHCPV6_SERVER_PORT), 0, ALL_DHCPV6_SERVERS, 0};
 558         struct iovec iov[2] = {{&hdr, sizeof(hdr)}, {(void*)data, len}};
 559         odhcpd_send(master->dhcpv6_event.uloop.fd, &dhcpv6_servers, iov, 2, master);
 560 }