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 // Create socket and register events
  38 int dhcpv6_init(void)
  39 {
  40         dhcpv6_ia_init();
  41         return 0;
  42 }
  43
  44 int dhcpv6_setup_interface(struct interface *iface, bool enable)
  45 {
  46         if (iface->dhcpv6_event.uloop.fd > 0) {
  47                 uloop_fd_delete(&iface->dhcpv6_event.uloop);
  48                 close(iface->dhcpv6_event.uloop.fd);
  49                 iface->dhcpv6_event.uloop.fd = -1;
  50         }
  51
  52         // Configure multicast settings
  53         if (enable && iface->dhcpv6) {
  54                 int sock = socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
  55                 if (sock < 0) {
  56                         syslog(LOG_ERR, "Failed to create DHCPv6 server socket: %s",
  57                                         strerror(errno));
  58                         return -1;
  59                 }
  60
  61                 // Basic IPv6 configuration
  62                 setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, iface->ifname, strlen(iface->ifname));
  63
  64                 int val = 1;
  65                 setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
  66                 setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
  67                 setsockopt(sock, IPPROTO_IPV6, IPV6_RECVPKTINFO, &val, sizeof(val));
  68
  69                 val = DHCPV6_HOP_COUNT_LIMIT;
  70                 setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &val, sizeof(val));
  71
  72                 val = 0;
  73                 setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &val, sizeof(val));
  74
  75                 struct sockaddr_in6 bind_addr = {AF_INET6, htons(DHCPV6_SERVER_PORT),
  76                                         0, IN6ADDR_ANY_INIT, 0};
  77
  78                 if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr))) {
  79                         syslog(LOG_ERR, "Failed to open DHCPv6 server socket: %s",
  80                                         strerror(errno));
  81                         return -1;
  82                 }
  83
  84                 struct ipv6_mreq relay = {ALL_DHCPV6_RELAYS, iface->ifindex};
  85                 struct ipv6_mreq server = {ALL_DHCPV6_SERVERS, iface->ifindex};
  86                 setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &relay, sizeof(relay));
  87
  88                 if (iface->dhcpv6 == MODE_SERVER)
  89                         setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &server, sizeof(server));
  90
  91                 iface->dhcpv6_event.uloop.fd = sock;
  92                 iface->dhcpv6_event.handle_dgram = handle_dhcpv6;
  93                 odhcpd_register(&iface->dhcpv6_event);
  94         }
  95
  96         return dhcpv6_setup_ia_interface(iface, enable);
  97 }
  98
  99 enum {
 100         IOV_NESTED = 0,
 101         IOV_DEST,
 102         IOV_MAXRT,
 103 #define IOV_STAT IOV_MAXRT
 104         IOV_DNS,
 105         IOV_DNS_ADDR,
 106         IOV_SEARCH,
 107         IOV_SEARCH_DOMAIN,
 108         IOV_PDBUF,
 109 #define IOV_REFRESH IOV_PDBUF
 110         IOV_CERID,
 111         IOV_DHCPV6_RAW,
 112         IOV_RELAY_MSG,
 113         IOV_TOTAL
 114 };
 115
 116 static void handle_nested_message(uint8_t *data, size_t len,
 117                 uint8_t **opts, uint8_t **end, struct iovec iov[IOV_TOTAL - 1])
 118 {
 119         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 120         if (iov[IOV_NESTED].iov_base == NULL) {
 121                 iov[IOV_NESTED].iov_base = data;
 122                 iov[IOV_NESTED].iov_len = len;
 123         }
 124
 125         if (len < sizeof(struct dhcpv6_client_header))
 126                 return;
 127
 128         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW) {
 129                 iov[IOV_NESTED].iov_len = data - (uint8_t*)iov[IOV_NESTED].iov_base;
 130                 struct dhcpv6_client_header *hdr = (void*)data;
 131                 *opts = (uint8_t*)&hdr[1];
 132                 *end = data + len;
 133                 return;
 134         }
 135
 136         uint16_t otype, olen;
 137         uint8_t *odata;
 138         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 139                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 140                         iov[IOV_RELAY_MSG].iov_base = odata + olen;
 141                         iov[IOV_RELAY_MSG].iov_len = (((uint8_t*)iov[IOV_NESTED].iov_base) +
 142                                         iov[IOV_NESTED].iov_len) - (odata + olen);
 143                         handle_nested_message(odata, olen, opts, end, iov);
 144                         return;
 145                 }
 146         }
 147 }
 148
 149
 150 static void update_nested_message(uint8_t *data, size_t len, ssize_t pdiff)
 151 {
 152         struct dhcpv6_relay_header *hdr = (struct dhcpv6_relay_header*)data;
 153         if (hdr->msg_type != DHCPV6_MSG_RELAY_FORW)
 154                 return;
 155
 156         hdr->msg_type = DHCPV6_MSG_RELAY_REPL;
 157
 158         uint16_t otype, olen;
 159         uint8_t *odata;
 160         dhcpv6_for_each_option(hdr->options, data + len, otype, olen, odata) {
 161                 if (otype == DHCPV6_OPT_RELAY_MSG) {
 162                         olen += pdiff;
 163                         odata[-2] = (olen >> 8) & 0xff;
 164                         odata[-1] = olen & 0xff;
 165                         update_nested_message(odata, olen - pdiff, pdiff);
 166                         return;
 167                 }
 168         }
 169 }
 170
 171 // Simple DHCPv6-server for information requests
 172 static void handle_client_request(void *addr, void *data, size_t len,
 173                 struct interface *iface, void *dest_addr)
 174 {
 175         struct dhcpv6_client_header *hdr = data;
 176
 177         if (len < sizeof(*hdr))
 178                 return;
 179
 180         syslog(LOG_NOTICE, "Got DHCPv6 request");
 181
 182         // Construct reply message
 183         struct __attribute__((packed)) {
 184                 uint8_t msg_type;
 185                 uint8_t tr_id[3];
 186                 uint16_t serverid_type;
 187                 uint16_t serverid_length;
 188                 uint16_t duid_type;
 189                 uint16_t hardware_type;
 190                 uint8_t mac[6];
 191                 uint16_t clientid_type;
 192                 uint16_t clientid_length;
 193                 uint8_t clientid_buf[130];
 194         } dest = {
 195                 .msg_type = DHCPV6_MSG_REPLY,
 196                 .serverid_type = htons(DHCPV6_OPT_SERVERID),
 197                 .serverid_length = htons(10),
 198                 .duid_type = htons(3),
 199                 .hardware_type = htons(1),
 200                 .clientid_type = htons(DHCPV6_OPT_CLIENTID),
 201                 .clientid_buf = {0}
 202         };
 203         odhcpd_get_mac(iface, dest.mac);
 204
 205         struct __attribute__((packed)) {
 206                 uint16_t type;
 207                 uint16_t len;
 208                 uint32_t value;
 209         } maxrt = {htons(DHCPV6_OPT_SOL_MAX_RT), htons(sizeof(maxrt) - 4),
 210                         htonl(60)};
 211
 212         struct __attribute__((packed)) {
 213                 uint16_t type;
 214                 uint16_t len;
 215                 uint16_t value;
 216         } stat = {htons(DHCPV6_OPT_STATUS), htons(sizeof(stat) - 4),
 217                         htons(DHCPV6_STATUS_USEMULTICAST)};
 218
 219         struct __attribute__((packed)) {
 220                 uint16_t type;
 221                 uint16_t len;
 222                 uint32_t value;
 223         } refresh = {htons(DHCPV6_OPT_INFO_REFRESH), htons(sizeof(uint32_t)),
 224                         htonl(600)};
 225
 226         struct in6_addr dns_addr, *dns_addr_ptr = iface->dns;
 227         size_t dns_cnt = iface->dns_cnt;
 228
 229         if ((dns_cnt == 0) &&
 230                 !odhcpd_get_interface_dns_addr(iface, &dns_addr)) {
 231                 dns_addr_ptr = &dns_addr;
 232                 dns_cnt = 1;
 233         }
 234
 235         struct {
 236                 uint16_t type;
 237                 uint16_t len;
 238         } dns = {htons(DHCPV6_OPT_DNS_SERVERS), htons(dns_cnt * sizeof(*dns_addr_ptr))};
 239
 240
 241
 242         // DNS Search options
 243         uint8_t search_buf[256], *search_domain = iface->search;
 244         size_t search_len = iface->search_len;
 245
 246         if (!search_domain && !res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 247                 int len = dn_comp(_res.dnsrch[0], search_buf,
 248                                 sizeof(search_buf), NULL, NULL);
 249                 if (len > 0) {
 250                         search_domain = search_buf;
 251                         search_len = len;
 252                 }
 253         }
 254
 255         struct {
 256                 uint16_t type;
 257                 uint16_t len;
 258         } search = {htons(DHCPV6_OPT_DNS_DOMAIN), htons(search_len)};
 259
 260
 261         struct dhcpv6_cer_id cerid = {
 262 #ifdef EXT_CER_ID
 263                 .type = htons(EXT_CER_ID),
 264 #endif
 265                 .len = htons(36),
 266                 .addr = iface->dhcpv6_pd_cer,
 267         };
 268
 269
 270         uint8_t pdbuf[512];
 271         struct iovec iov[IOV_TOTAL] = {
 272                 [IOV_NESTED] = {NULL, 0},
 273                 [IOV_DEST] = {&dest, (uint8_t*)&dest.clientid_type - (uint8_t*)&dest},
 274                 [IOV_MAXRT] = {&maxrt, sizeof(maxrt)},
 275                 [IOV_DNS] = {&dns, (dns_cnt) ? sizeof(dns) : 0},
 276                 [IOV_DNS_ADDR] = {dns_addr_ptr, dns_cnt * sizeof(*dns_addr_ptr)},
 277                 [IOV_SEARCH] = {&search, (search_len) ? sizeof(search) : 0},
 278                 [IOV_SEARCH_DOMAIN] = {search_domain, search_len},
 279                 [IOV_PDBUF] = {pdbuf, 0},
 280                 [IOV_CERID] = {&cerid, 0},
 281                 [IOV_DHCPV6_RAW] = {iface->dhcpv6_raw, iface->dhcpv6_raw_len},
 282                 [IOV_RELAY_MSG] = {NULL, 0}
 283         };
 284
 285         uint8_t *opts = (uint8_t*)&hdr[1], *opts_end = (uint8_t*)data + len;
 286         if (hdr->msg_type == DHCPV6_MSG_RELAY_FORW)
 287                 handle_nested_message(data, len, &opts, &opts_end, iov);
 288
 289         memcpy(dest.tr_id, &opts[-3], sizeof(dest.tr_id));
 290
 291         if (opts[-4] == DHCPV6_MSG_ADVERTISE || opts[-4] == DHCPV6_MSG_REPLY || opts[-4] == DHCPV6_MSG_RELAY_REPL)
 292                 return;
 293
 294         if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 295                 (opts[-4] == DHCPV6_MSG_SOLICIT || opts[-4] == DHCPV6_MSG_CONFIRM ||
 296                  opts[-4] == DHCPV6_MSG_REBIND || opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST))
 297                 return;
 298
 299         if (opts[-4] == DHCPV6_MSG_SOLICIT) {
 300                 dest.msg_type = DHCPV6_MSG_ADVERTISE;
 301         } else if (opts[-4] == DHCPV6_MSG_INFORMATION_REQUEST) {
 302                 iov[IOV_REFRESH].iov_base = &refresh;
 303                 iov[IOV_REFRESH].iov_len = sizeof(refresh);
 304
 305                 // Return inf max rt option in reply to information request
 306                 maxrt.type = htons(DHCPV6_OPT_INF_MAX_RT);
 307         }
 308
 309         // Go through options and find what we need
 310         uint16_t otype, olen;
 311         uint8_t *odata;
 312         dhcpv6_for_each_option(opts, opts_end, otype, olen, odata) {
 313                 if (otype == DHCPV6_OPT_CLIENTID && olen <= 130) {
 314                         dest.clientid_length = htons(olen);
 315                         memcpy(dest.clientid_buf, odata, olen);
 316                         iov[IOV_DEST].iov_len += 4 + olen;
 317                 } else if (otype == DHCPV6_OPT_SERVERID) {
 318                         if (olen != ntohs(dest.serverid_length) ||
 319                                         memcmp(odata, &dest.duid_type, olen))
 320                                 return; // Not for us
 321                 } else if (iface->filter_class && otype == DHCPV6_OPT_USER_CLASS) {
 322                         uint8_t *c = odata, *cend = &odata[olen];
 323                         for (; &c[2] <= cend && &c[2 + (c[0] << 8) + c[1]] <= cend; c = &c[2 + (c[0] << 8) + c[1]]) {
 324                                 size_t elen = strlen(iface->filter_class);
 325                                 if (((((size_t)c[0]) << 8) | c[1]) == elen && !memcmp(&c[2], iface->filter_class, elen))
 326                                         return; // Ignore from homenet
 327                         }
 328                 } else if (otype == DHCPV6_OPT_IA_PD) {
 329 #ifdef EXT_CER_ID
 330                         iov[IOV_CERID].iov_len = sizeof(cerid);
 331
 332                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)) {
 333                                 struct odhcpd_ipaddr *addrs;
 334                                 ssize_t len = netlink_get_interface_addrs(0, true, &addrs);
 335
 336                                 for (ssize_t i = 0; i < len; ++i)
 337                                         if (IN6_IS_ADDR_UNSPECIFIED(&cerid.addr)
 338                                                         || memcmp(&addrs[i].addr, &cerid.addr, sizeof(cerid.addr)) < 0)
 339                                                 cerid.addr = addrs[i].addr.in6;
 340
 341                                 free(addrs);
 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 == MODE_SERVER) {
 383                 handle_client_request(addr, data, len, iface, dest_addr);
 384         } else if (iface->dhcpv6 == MODE_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                 const struct in6_addr *rewrite = iface->dns;
 459                 struct in6_addr addr;
 460                 size_t rewrite_cnt = iface->dns_cnt;
 461
 462                 if (rewrite_cnt == 0) {
 463                         if (odhcpd_get_interface_dns_addr(iface, &addr))
 464                                 return; // Unable to get interface address
 465
 466                         rewrite = &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 static struct odhcpd_ipaddr *relay_link_address(struct interface *iface)
 482 {
 483         struct odhcpd_ipaddr *addr = NULL;
 484         time_t now = odhcpd_time();
 485
 486         for (size_t i = 0; i < iface->addr6_len; i++) {
 487                 if (iface->addr6[i].valid <= (uint32_t)now)
 488                         continue;
 489
 490                 if (iface->addr6[i].preferred > (uint32_t)now) {
 491                         addr = &iface->addr6[i];
 492                         break;
 493                 }
 494
 495                 if (!addr || (iface->addr6[i].valid > addr->valid))
 496                         addr = &iface->addr6[i];
 497         }
 498
 499         return addr;
 500 }
 501
 502 // Relay client request (regular DHCPv6-relay)
 503 static void relay_client_request(struct sockaddr_in6 *source,
 504                 const void *data, size_t len, struct interface *iface)
 505 {
 506         struct interface *master = odhcpd_get_master_interface();
 507         const struct dhcpv6_relay_header *h = data;
 508         if (!master || master->dhcpv6 != MODE_RELAY ||
 509                         h->msg_type == DHCPV6_MSG_RELAY_REPL ||
 510                         h->msg_type == DHCPV6_MSG_RECONFIGURE ||
 511                         h->msg_type == DHCPV6_MSG_REPLY ||
 512                         h->msg_type == DHCPV6_MSG_ADVERTISE)
 513                 return; // Invalid message types for client
 514
 515         syslog(LOG_NOTICE, "Got a DHCPv6-request");
 516
 517         // Construct our forwarding envelope
 518         struct dhcpv6_relay_forward_envelope hdr = {
 519                 .msg_type = DHCPV6_MSG_RELAY_FORW,
 520                 .hop_count = 0,
 521                 .interface_id_type = htons(DHCPV6_OPT_INTERFACE_ID),
 522                 .interface_id_len = htons(sizeof(uint32_t)),
 523                 .relay_message_type = htons(DHCPV6_OPT_RELAY_MSG),
 524                 .relay_message_len = htons(len),
 525         };
 526
 527         if (h->msg_type == DHCPV6_MSG_RELAY_FORW) { // handle relay-forward
 528                 if (h->hop_count >= DHCPV6_HOP_COUNT_LIMIT)
 529                         return; // Invalid hop count
 530                 else
 531                         hdr.hop_count = h->hop_count + 1;
 532         }
 533
 534         // use memcpy here as the destination fields are unaligned
 535         uint32_t ifindex = iface->ifindex;
 536         memcpy(&hdr.peer_address, &source->sin6_addr, sizeof(struct in6_addr));
 537         memcpy(&hdr.interface_id_data, &ifindex, sizeof(ifindex));
 538
 539         // Detect public IP of slave interface to use as link-address
 540         struct odhcpd_ipaddr *ip = relay_link_address(iface);
 541         if (!ip) {
 542                 // No suitable address! Is the slave not configured yet?
 543                 // Detect public IP of master interface and use it instead
 544                 // This is WRONG and probably violates the RFC. However
 545                 // otherwise we have a hen and egg problem because the
 546                 // slave-interface cannot be auto-configured.
 547                 ip = relay_link_address(master);
 548                 if (!ip)
 549                         return; // Could not obtain a suitable address
 550         }
 551
 552         memcpy(&hdr.link_address, &ip->addr.in6, sizeof(hdr.link_address));
 553
 554         struct sockaddr_in6 dhcpv6_servers = {AF_INET6,
 555                         htons(DHCPV6_SERVER_PORT), 0, ALL_DHCPV6_SERVERS, 0};
 556         struct iovec iov[2] = {{&hdr, sizeof(hdr)}, {(void*)data, len}};
 557         odhcpd_send(master->dhcpv6_event.uloop.fd, &dhcpv6_servers, iov, 2, master);
 558 }