src/router.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 #include <errno.h>
  16 #include <fcntl.h>
  17 #include <signal.h>
  18 #include <resolv.h>
  19 #include <stdio.h>
  20 #include <stdlib.h>
  21 #include <unistd.h>
  22 #include <stdbool.h>
  23 #include <net/route.h>
  24
  25 #include "router.h"
  26 #include "odhcpd.h"
  27
  28
  29 static void forward_router_solicitation(const struct interface *iface);
  30 static void forward_router_advertisement(uint8_t *data, size_t len);
  31
  32 static void handle_icmpv6(void *addr, void *data, size_t len,
  33                 struct interface *iface, void *dest);
  34 static void trigger_router_advert(struct uloop_timeout *event);
  35 static void sigusr1_refresh(int signal);
  36
  37 static struct odhcpd_event router_event = {{.fd = -1}, handle_icmpv6};
  38
  39 static FILE *fp_route = NULL;
  40 #define RA_IOV_LEN 6
  41
  42
  43 int init_router(void)
  44 {
  45         // Open ICMPv6 socket
  46         int sock = socket(AF_INET6, SOCK_RAW | SOCK_CLOEXEC, IPPROTO_ICMPV6);
  47         if (sock < 0 && errno != EAFNOSUPPORT) {
  48                 syslog(LOG_ERR, "Failed to open RAW-socket: %s", strerror(errno));
  49                 return -1;
  50         }
  51
  52         // Let the kernel compute our checksums
  53         int val = 2;
  54         setsockopt(sock, IPPROTO_RAW, IPV6_CHECKSUM, &val, sizeof(val));
  55
  56         // This is required by RFC 4861
  57         val = 255;
  58         setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &val, sizeof(val));
  59         setsockopt(sock, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &val, sizeof(val));
  60
  61         // We need to know the source interface
  62         val = 1;
  63         setsockopt(sock, IPPROTO_IPV6, IPV6_RECVPKTINFO, &val, sizeof(val));
  64         setsockopt(sock, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &val, sizeof(val));
  65
  66         // Don't loop back
  67         val = 0;
  68         setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &val, sizeof(val));
  69
  70         // Filter ICMPv6 package types
  71         struct icmp6_filter filt;
  72         ICMP6_FILTER_SETBLOCKALL(&filt);
  73         ICMP6_FILTER_SETPASS(ND_ROUTER_ADVERT, &filt);
  74         ICMP6_FILTER_SETPASS(ND_ROUTER_SOLICIT, &filt);
  75         setsockopt(sock, IPPROTO_ICMPV6, ICMP6_FILTER, &filt, sizeof(filt));
  76
  77         // Register socket
  78         router_event.uloop.fd = sock;
  79         odhcpd_register(&router_event);
  80
  81         if (!(fp_route = fopen("/proc/net/ipv6_route", "r")))
  82                 syslog(LOG_ERR, "Failed to open routing table: %s",
  83                                 strerror(errno));
  84
  85         signal(SIGUSR1, sigusr1_refresh);
  86         return 0;
  87 }
  88
  89
  90 int setup_router_interface(struct interface *iface, bool enable)
  91 {
  92         if (!fp_route || router_event.uloop.fd < 0)
  93                 return -1;
  94
  95         struct ipv6_mreq all_nodes = {ALL_IPV6_NODES, iface->ifindex};
  96         struct ipv6_mreq all_routers = {ALL_IPV6_ROUTERS, iface->ifindex};
  97
  98         uloop_timeout_cancel(&iface->timer_rs);
  99         iface->timer_rs.cb = NULL;
 100
 101         setsockopt(router_event.uloop.fd, IPPROTO_IPV6, IPV6_DROP_MEMBERSHIP,
 102                         &all_nodes, sizeof(all_nodes));
 103         setsockopt(router_event.uloop.fd, IPPROTO_IPV6, IPV6_DROP_MEMBERSHIP,
 104                         &all_routers, sizeof(all_routers));
 105
 106         if (!enable) {
 107                 if (iface->ra)
 108                         trigger_router_advert(&iface->timer_rs);
 109         } else {
 110                 void *mreq = &all_routers;
 111
 112                 if (iface->ra == RELAYD_RELAY && iface->master) {
 113                         mreq = &all_nodes;
 114                         forward_router_solicitation(iface);
 115                 } else if (iface->ra == RELAYD_SERVER && !iface->master) {
 116                         iface->timer_rs.cb = trigger_router_advert;
 117                         trigger_router_advert(&iface->timer_rs);
 118                 }
 119
 120                 if (iface->ra == RELAYD_RELAY || (iface->ra == RELAYD_SERVER && !iface->master))
 121                         setsockopt(router_event.uloop.fd, IPPROTO_IPV6,
 122                                         IPV6_ADD_MEMBERSHIP, mreq, sizeof(all_nodes));
 123         }
 124         return 0;
 125 }
 126
 127
 128 // Signal handler to resend all RDs
 129 static void sigusr1_refresh(_unused int signal)
 130 {
 131         struct interface *iface;
 132         list_for_each_entry(iface, &interfaces, head)
 133                 if (iface->ra == RELAYD_SERVER && !iface->master)
 134                         uloop_timeout_set(&iface->timer_rs, 1000);
 135 }
 136
 137 static bool router_icmpv6_valid(struct sockaddr_in6 *source, uint8_t *data, size_t len)
 138 {
 139         struct icmp6_hdr *hdr = (struct icmp6_hdr *)data;
 140         struct icmpv6_opt *opt, *end = (struct icmpv6_opt*)&data[len];
 141
 142         /* Hoplimit is already checked in odhcpd_receive_packets */
 143         if (len < sizeof(*hdr) || hdr->icmp6_code)
 144                 return false;
 145
 146         switch (hdr->icmp6_type) {
 147         case ND_ROUTER_ADVERT:
 148                 if (!IN6_IS_ADDR_LINKLOCAL(&source->sin6_addr))
 149                         return false;
 150
 151                 opt = (struct icmpv6_opt *)((struct nd_router_advert *)data + 1);
 152                 break;
 153
 154         case ND_ROUTER_SOLICIT:
 155                 opt = (struct icmpv6_opt *)((struct nd_router_solicit *)data + 1);
 156                 break;
 157
 158         default:
 159                 return false;
 160         }
 161
 162         icmpv6_for_each_option(opt, opt, end)
 163                 if (opt->type == ND_OPT_SOURCE_LINKADDR &&
 164                                 IN6_IS_ADDR_UNSPECIFIED(&source->sin6_addr) &&
 165                                 hdr->icmp6_type == ND_ROUTER_SOLICIT)
 166                         return false;
 167
 168         // Check all options parsed successfully
 169         return opt == end;
 170 }
 171
 172
 173 // Detect whether a default route exists, also find the source prefixes
 174 static bool parse_routes(struct odhcpd_ipaddr *n, ssize_t len)
 175 {
 176         rewind(fp_route);
 177
 178         char line[512], ifname[16];
 179         bool found_default = false;
 180         struct odhcpd_ipaddr p = {IN6ADDR_ANY_INIT, 0, 0, 0, 0};
 181         while (fgets(line, sizeof(line), fp_route)) {
 182                 uint32_t rflags;
 183                 if (sscanf(line, "00000000000000000000000000000000 00 "
 184                                 "%*s %*s %*s %*s %*s %*s %*s %15s", ifname) &&
 185                                 strcmp(ifname, "lo")) {
 186                         found_default = true;
 187                 } else if (sscanf(line, "%8" SCNx32 "%8" SCNx32 "%*8" SCNx32 "%*8" SCNx32 " %hhx %*s "
 188                                 "%*s 00000000000000000000000000000000 %*s %*s %*s %" SCNx32 " lo",
 189                                 &p.addr.s6_addr32[0], &p.addr.s6_addr32[1], &p.prefix, &rflags) &&
 190                                 p.prefix > 0 && (rflags & RTF_NONEXTHOP) && (rflags & RTF_REJECT)) {
 191                         // Find source prefixes by scanning through unreachable-routes
 192                         p.addr.s6_addr32[0] = htonl(p.addr.s6_addr32[0]);
 193                         p.addr.s6_addr32[1] = htonl(p.addr.s6_addr32[1]);
 194
 195                         for (ssize_t i = 0; i < len; ++i) {
 196                                 if (n[i].prefix <= 64 && n[i].prefix >= p.prefix &&
 197                                                 !odhcpd_bmemcmp(&p.addr, &n[i].addr, p.prefix)) {
 198                                         n[i].dprefix = p.prefix;
 199                                         break;
 200                                 }
 201                         }
 202
 203                 }
 204         }
 205
 206         return found_default;
 207 }
 208
 209 // Router Advert server mode
 210 static uint64_t send_router_advert(struct interface *iface, const struct in6_addr *from)
 211 {
 212         int mtu = odhcpd_get_interface_config(iface->ifname, "mtu");
 213         int hlim = odhcpd_get_interface_config(iface->ifname, "hop_limit");
 214
 215         if (mtu < 1280)
 216                 mtu = 1280;
 217
 218         struct {
 219                 struct nd_router_advert h;
 220                 struct icmpv6_opt lladdr;
 221                 struct nd_opt_mtu mtu;
 222                 struct nd_opt_prefix_info prefix[RELAYD_MAX_PREFIXES];
 223         } adv = {
 224                 .h = {{.icmp6_type = ND_ROUTER_ADVERT, .icmp6_code = 0}, 0, 0},
 225                 .lladdr = {ND_OPT_SOURCE_LINKADDR, 1, {0}},
 226                 .mtu = {ND_OPT_MTU, 1, 0, htonl(mtu)},
 227         };
 228
 229         if (hlim > 0)
 230                 adv.h.nd_ra_curhoplimit = hlim;
 231
 232         if (iface->dhcpv6)
 233                 adv.h.nd_ra_flags_reserved = ND_RA_FLAG_OTHER;
 234
 235         if (iface->managed >= RELAYD_MANAGED_MFLAG)
 236                 adv.h.nd_ra_flags_reserved |= ND_RA_FLAG_MANAGED;
 237
 238         if (iface->route_preference < 0)
 239                 adv.h.nd_ra_flags_reserved |= ND_RA_PREF_LOW;
 240         else if (iface->route_preference > 0)
 241                 adv.h.nd_ra_flags_reserved |= ND_RA_PREF_HIGH;
 242         odhcpd_get_mac(iface, adv.lladdr.data);
 243
 244         // If not currently shutting down
 245         struct odhcpd_ipaddr addrs[RELAYD_MAX_PREFIXES];
 246         ssize_t ipcnt = 0;
 247         uint64_t minvalid = UINT64_MAX;
 248         uint64_t maxvalid = 0;
 249
 250         // If not shutdown
 251         if (iface->timer_rs.cb) {
 252                 ipcnt = odhcpd_get_interface_addresses(iface->ifindex,
 253                                 addrs, ARRAY_SIZE(addrs));
 254
 255                 // Check default route
 256                 if (iface->default_router > 1)
 257                         adv.h.nd_ra_router_lifetime = htons(iface->default_router);
 258                 if (parse_routes(addrs, ipcnt))
 259                         adv.h.nd_ra_router_lifetime = htons(1);
 260         }
 261
 262         // Construct Prefix Information options
 263         size_t cnt = 0;
 264
 265         struct in6_addr dns_pref = IN6ADDR_ANY_INIT, *dns_addr = &dns_pref;
 266         uint32_t dns_time = 0;
 267         size_t dns_cnt = 1;
 268
 269         for (ssize_t i = 0; i < ipcnt; ++i) {
 270                 struct odhcpd_ipaddr *addr = &addrs[i];
 271                 if (addr->prefix > 96)
 272                         continue; // Address not suitable
 273
 274                 if (addr->preferred > MaxValidTime)
 275                         addr->preferred = MaxValidTime;
 276
 277                 if (addr->valid > MaxValidTime)
 278                         addr->valid = MaxValidTime;
 279
 280                 struct nd_opt_prefix_info *p = NULL;
 281                 for (size_t i = 0; i < cnt; ++i) {
 282                         if (addr->prefix == adv.prefix[i].nd_opt_pi_prefix_len &&
 283                                         !odhcpd_bmemcmp(&adv.prefix[i].nd_opt_pi_prefix,
 284                                         &addr->addr, addr->prefix))
 285                                 p = &adv.prefix[i];
 286                 }
 287
 288                 if (!p) {
 289                         if (cnt >= ARRAY_SIZE(adv.prefix))
 290                                 break;
 291
 292                         p = &adv.prefix[cnt++];
 293                 }
 294
 295                 if (addr->preferred > 0 &&
 296                                 minvalid > 1000ULL * addr->valid)
 297                         minvalid = 1000ULL * addr->valid;
 298
 299                 if (maxvalid < 1000ULL * addr->valid)
 300                         maxvalid = 1000ULL * addr->valid;
 301
 302                 if (((addr->addr.s6_addr[0] & 0xfe) != 0xfc || iface->default_router)
 303                                 && ntohs(adv.h.nd_ra_router_lifetime) < addr->valid)
 304                         adv.h.nd_ra_router_lifetime = htons(addr->valid);
 305
 306                 odhcpd_bmemcpy(&p->nd_opt_pi_prefix, &addr->addr,
 307                                 (iface->ra_advrouter) ? 128 : addr->prefix);
 308                 p->nd_opt_pi_type = ND_OPT_PREFIX_INFORMATION;
 309                 p->nd_opt_pi_len = 4;
 310                 p->nd_opt_pi_prefix_len = (addr->prefix < 64) ? 64 : addr->prefix;
 311                 p->nd_opt_pi_flags_reserved = 0;
 312                 if (!iface->ra_not_onlink)
 313                         p->nd_opt_pi_flags_reserved |= ND_OPT_PI_FLAG_ONLINK;
 314                 if (iface->managed < RELAYD_MANAGED_NO_AFLAG && addr->prefix <= 64)
 315                         p->nd_opt_pi_flags_reserved |= ND_OPT_PI_FLAG_AUTO;
 316                 if (iface->ra_advrouter)
 317                         p->nd_opt_pi_flags_reserved |= ND_OPT_PI_FLAG_RADDR;
 318                 p->nd_opt_pi_valid_time = htonl(addr->valid);
 319                 p->nd_opt_pi_preferred_time = htonl(addr->preferred);
 320
 321                 if (addr->preferred > dns_time) {
 322                         dns_time = addr->preferred;
 323                         dns_pref = addr->addr;
 324                 }
 325         }
 326
 327         if (!iface->default_router && ntohs(adv.h.nd_ra_router_lifetime) == 1) {
 328                 syslog(LOG_WARNING, "A default route is present but there is no public prefix "
 329                                 "on %s thus we don't announce a default route!", iface->ifname);
 330                 adv.h.nd_ra_router_lifetime = 0;
 331         }
 332
 333         // DNS Recursive DNS
 334         if (iface->dns_cnt > 0) {
 335                 dns_addr = iface->dns;
 336                 dns_cnt = iface->dns_cnt;
 337                 dns_time = 0;
 338         }
 339
 340         if (!dns_addr || IN6_IS_ADDR_UNSPECIFIED(dns_addr))
 341                 dns_cnt = 0;
 342
 343         struct {
 344                 uint8_t type;
 345                 uint8_t len;
 346                 uint8_t pad;
 347                 uint8_t pad2;
 348                 uint32_t lifetime;
 349         } dns = {ND_OPT_RECURSIVE_DNS, (1 + (2 * dns_cnt)), 0, 0, htonl(dns_time)};
 350
 351
 352
 353         // DNS Search options
 354         uint8_t search_buf[256], *search_domain = iface->search;
 355         size_t search_len = iface->search_len, search_padded = 0;
 356
 357         if (!search_domain && !res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 358                 int len = dn_comp(_res.dnsrch[0], search_buf,
 359                                 sizeof(search_buf), NULL, NULL);
 360                 if (len > 0) {
 361                         search_domain = search_buf;
 362                         search_len = len;
 363                 }
 364         }
 365
 366         if (search_len > 0)
 367                 search_padded = ((search_len + 7) & (~7)) + 8;
 368
 369         struct {
 370                 uint8_t type;
 371                 uint8_t len;
 372                 uint8_t pad;
 373                 uint8_t pad2;
 374                 uint32_t lifetime;
 375                 uint8_t name[];
 376         } *search = alloca(sizeof(*search) + search_padded);
 377
 378         search->type = ND_OPT_DNS_SEARCH;
 379         search->len = search_len ? ((sizeof(*search) + search_padded) / 8) : 0;
 380         search->pad = 0;
 381         search->pad2 = 0;
 382         memcpy(search->name, search_domain, search_len);
 383         memset(&search->name[search_len], 0, search_padded - search_len);
 384
 385
 386         size_t routes_cnt = 0;
 387         struct {
 388                 uint8_t type;
 389                 uint8_t len;
 390                 uint8_t prefix;
 391                 uint8_t flags;
 392                 uint32_t lifetime;
 393                 uint32_t addr[4];
 394         } routes[RELAYD_MAX_PREFIXES];
 395
 396         for (ssize_t i = 0; i < ipcnt; ++i) {
 397                 struct odhcpd_ipaddr *addr = &addrs[i];
 398                 if (addr->dprefix > 64 || addr->dprefix == 0 ||
 399                                 (addr->dprefix == 64 && addr->prefix == 64)) {
 400                         continue; // Address not suitable
 401                 } else if (addr->dprefix > 32) {
 402                         addr->addr.s6_addr32[1] &= htonl(~((1U << (64 - addr->dprefix)) - 1));
 403                 } else if (addr->dprefix <= 32) {
 404                         addr->addr.s6_addr32[0] &= htonl(~((1U << (32 - addr->dprefix)) - 1));
 405                         addr->addr.s6_addr32[1] = 0;
 406                 }
 407
 408                 routes[routes_cnt].type = ND_OPT_ROUTE_INFO;
 409                 routes[routes_cnt].len = sizeof(*routes) / 8;
 410                 routes[routes_cnt].prefix = addr->dprefix;
 411                 routes[routes_cnt].flags = 0;
 412                 if (iface->route_preference < 0)
 413                         routes[routes_cnt].flags |= ND_RA_PREF_LOW;
 414                 else if (iface->route_preference > 0)
 415                         routes[routes_cnt].flags |= ND_RA_PREF_HIGH;
 416                 routes[routes_cnt].lifetime = htonl(addr->valid);
 417                 routes[routes_cnt].addr[0] = addr->addr.s6_addr32[0];
 418                 routes[routes_cnt].addr[1] = addr->addr.s6_addr32[1];
 419                 routes[routes_cnt].addr[2] = 0;
 420                 routes[routes_cnt].addr[3] = 0;
 421
 422                 ++routes_cnt;
 423         }
 424
 425         // Calculate periodic transmit
 426         int msecs = 0;
 427         uint32_t maxival = iface->ra_maxinterval * 1000;
 428         uint32_t minival;
 429
 430         if (maxival < 4000 || maxival > MaxRtrAdvInterval * 1000)
 431                 maxival = MaxRtrAdvInterval * 1000;
 432
 433         if (maxival > minvalid / 3) {
 434                 maxival = minvalid / 3;
 435
 436                 if (maxival < 4000)
 437                         maxival = 4000;
 438         }
 439
 440         minival = (maxival * 3) / 4;
 441
 442         search->lifetime = htonl(maxvalid / 1000);
 443
 444         if (!dns.lifetime)
 445                 dns.lifetime = search->lifetime;
 446
 447         odhcpd_urandom(&msecs, sizeof(msecs));
 448         msecs = (labs(msecs) % (maxival - minival)) + minival;
 449
 450         struct icmpv6_opt adv_interval = {
 451                 .type = ND_OPT_RTR_ADV_INTERVAL,
 452                 .len = 1,
 453                 .data = {0, 0, maxival >> 24, maxival >> 16, maxival >> 8, maxival}
 454         };
 455
 456         struct iovec iov[RA_IOV_LEN] = {
 457                         {&adv, (uint8_t*)&adv.prefix[cnt] - (uint8_t*)&adv},
 458                         {&routes, routes_cnt * sizeof(*routes)},
 459                         {&dns, (dns_cnt) ? sizeof(dns) : 0},
 460                         {dns_addr, dns_cnt * sizeof(*dns_addr)},
 461                         {search, search->len * 8},
 462                         {&adv_interval, adv_interval.len * 8}};
 463         struct sockaddr_in6 dest = {AF_INET6, 0, 0, ALL_IPV6_NODES, 0};
 464
 465         if (from && !IN6_IS_ADDR_UNSPECIFIED(from))
 466                 dest.sin6_addr = *from;
 467
 468         odhcpd_send(router_event.uloop.fd,
 469                         &dest, iov, ARRAY_SIZE(iov), iface);
 470
 471         return msecs;
 472 }
 473
 474
 475 static void trigger_router_advert(struct uloop_timeout *event)
 476 {
 477         struct interface *iface = container_of(event, struct interface, timer_rs);
 478         int msecs = send_router_advert(iface, NULL);
 479
 480         // Rearm timer if not shut down
 481         if (event->cb)
 482                 uloop_timeout_set(event, msecs);
 483 }
 484
 485
 486 // Event handler for incoming ICMPv6 packets
 487 static void handle_icmpv6(void *addr, void *data, size_t len,
 488                 struct interface *iface, _unused void *dest)
 489 {
 490         struct icmp6_hdr *hdr = data;
 491         struct sockaddr_in6 *from = addr;
 492
 493         if (!router_icmpv6_valid(addr, data, len))
 494                 return;
 495
 496         if ((iface->ra == RELAYD_SERVER && !iface->master)) { // Server mode
 497                 if (hdr->icmp6_type == ND_ROUTER_SOLICIT)
 498                         send_router_advert(iface, &from->sin6_addr);
 499         } else if (iface->ra == RELAYD_RELAY) { // Relay mode
 500                 if (hdr->icmp6_type == ND_ROUTER_ADVERT && iface->master)
 501                         forward_router_advertisement(data, len);
 502                 else if (hdr->icmp6_type == ND_ROUTER_SOLICIT && !iface->master)
 503                         forward_router_solicitation(odhcpd_get_master_interface());
 504         }
 505 }
 506
 507
 508 // Forward router solicitation
 509 static void forward_router_solicitation(const struct interface *iface)
 510 {
 511         if (!iface)
 512                 return;
 513
 514         struct icmp6_hdr rs = {ND_ROUTER_SOLICIT, 0, 0, {{0}}};
 515         struct iovec iov = {&rs, sizeof(rs)};
 516         struct sockaddr_in6 all_routers =
 517                 {AF_INET6, 0, 0, ALL_IPV6_ROUTERS, iface->ifindex};
 518
 519         syslog(LOG_NOTICE, "Sending RS to %s", iface->ifname);
 520         odhcpd_send(router_event.uloop.fd, &all_routers, &iov, 1, iface);
 521 }
 522
 523
 524 // Handler for incoming router solicitations on slave interfaces
 525 static void forward_router_advertisement(uint8_t *data, size_t len)
 526 {
 527         struct nd_router_advert *adv = (struct nd_router_advert *)data;
 528
 529         // Rewrite options
 530         uint8_t *end = data + len;
 531         uint8_t *mac_ptr = NULL;
 532         struct in6_addr *dns_ptr = NULL;
 533         size_t dns_count = 0;
 534
 535         struct icmpv6_opt *opt;
 536         icmpv6_for_each_option(opt, &adv[1], end) {
 537                 if (opt->type == ND_OPT_SOURCE_LINKADDR) {
 538                         // Store address of source MAC-address
 539                         mac_ptr = opt->data;
 540                 } else if (opt->type == ND_OPT_RECURSIVE_DNS && opt->len > 1) {
 541                         // Check if we have to rewrite DNS
 542                         dns_ptr = (struct in6_addr*)&opt->data[6];
 543                         dns_count = (opt->len - 1) / 2;
 544                 }
 545         }
 546
 547         syslog(LOG_NOTICE, "Got a RA");
 548
 549         // Indicate a proxy, however we don't follow the rest of RFC 4389 yet
 550         adv->nd_ra_flags_reserved |= ND_RA_FLAG_PROXY;
 551
 552         // Forward advertisement to all slave interfaces
 553         struct sockaddr_in6 all_nodes = {AF_INET6, 0, 0, ALL_IPV6_NODES, 0};
 554         struct iovec iov = {data, len};
 555
 556         struct interface *iface;
 557         list_for_each_entry(iface, &interfaces, head) {
 558                 if (iface->ra != RELAYD_RELAY || iface->master)
 559                         continue;
 560
 561                 // Fixup source hardware address option
 562                 if (mac_ptr)
 563                         odhcpd_get_mac(iface, mac_ptr);
 564
 565                 // If we have to rewrite DNS entries
 566                 if (iface->always_rewrite_dns && dns_ptr && dns_count > 0) {
 567                         const struct in6_addr *rewrite = iface->dns;
 568                         struct in6_addr addr;
 569                         size_t rewrite_cnt = iface->dns_cnt;
 570
 571                         if (rewrite_cnt == 0) {
 572                                 if (odhcpd_get_preferred_interface_address(iface->ifindex, &addr) < 1)
 573                                         continue; // Unable to comply
 574
 575                                 rewrite = &addr;
 576                                 rewrite_cnt = 1;
 577                         }
 578
 579                         // Copy over any other addresses
 580                         for (size_t i = 0; i < dns_count; ++i) {
 581                                 size_t j = (i < rewrite_cnt) ? i : rewrite_cnt - 1;
 582                                 dns_ptr[i] = rewrite[j];
 583                         }
 584                 }
 585
 586                 odhcpd_send(router_event.uloop.fd, &all_nodes, &iov, 1, iface);
 587         }
 588 }