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                         uloop_timeout_set(&iface->timer_rs, 1000);
 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         time_t now = odhcpd_time();
 213         int mtu = odhcpd_get_interface_config(iface->ifname, "mtu");
 214         int hlim = odhcpd_get_interface_config(iface->ifname, "hop_limit");
 215
 216         if (mtu < 1280)
 217                 mtu = 1280;
 218
 219         struct {
 220                 struct nd_router_advert h;
 221                 struct icmpv6_opt lladdr;
 222                 struct nd_opt_mtu mtu;
 223                 struct nd_opt_prefix_info prefix[sizeof(iface->ia_addr) / sizeof(*iface->ia_addr)];
 224         } adv = {
 225                 .h = {{.icmp6_type = ND_ROUTER_ADVERT, .icmp6_code = 0}, 0, 0},
 226                 .lladdr = {ND_OPT_SOURCE_LINKADDR, 1, {0}},
 227                 .mtu = {ND_OPT_MTU, 1, 0, htonl(mtu)},
 228         };
 229
 230         if (hlim > 0)
 231                 adv.h.nd_ra_curhoplimit = hlim;
 232
 233         if (iface->dhcpv6)
 234                 adv.h.nd_ra_flags_reserved = ND_RA_FLAG_OTHER;
 235
 236         if (iface->managed >= RELAYD_MANAGED_MFLAG)
 237                 adv.h.nd_ra_flags_reserved |= ND_RA_FLAG_MANAGED;
 238
 239         if (iface->route_preference < 0)
 240                 adv.h.nd_ra_flags_reserved |= ND_RA_PREF_LOW;
 241         else if (iface->route_preference > 0)
 242                 adv.h.nd_ra_flags_reserved |= ND_RA_PREF_HIGH;
 243         odhcpd_get_mac(iface, adv.lladdr.data);
 244
 245         // If not currently shutting down
 246         struct odhcpd_ipaddr *addrs = NULL;
 247         ssize_t ipcnt = 0;
 248         int64_t minvalid = INT64_MAX;
 249         int64_t maxvalid = 0;
 250
 251         // If not shutdown
 252         if (iface->timer_rs.cb) {
 253                 addrs = iface->ia_addr;
 254                 ipcnt = iface->ia_addr_len;
 255
 256                 // Check default route
 257                 if (parse_routes(addrs, ipcnt))
 258                         adv.h.nd_ra_router_lifetime = htons(1);
 259                 if (iface->default_router > 1)
 260                         adv.h.nd_ra_router_lifetime = htons(iface->default_router);
 261         }
 262
 263         // Construct Prefix Information options
 264         size_t cnt = 0;
 265
 266         struct in6_addr dns_pref = IN6ADDR_ANY_INIT, *dns_addr = &dns_pref;
 267         uint32_t dns_time = 0;
 268         size_t dns_cnt = 1;
 269
 270         for (ssize_t i = 0; i < ipcnt; ++i) {
 271                 struct odhcpd_ipaddr *addr = &addrs[i];
 272                 if (addr->prefix > 96 || addr->valid <= (uint32_t)now)
 273                         continue; // Address not suitable
 274
 275                 struct nd_opt_prefix_info *p = NULL;
 276                 for (size_t i = 0; i < cnt; ++i) {
 277                         if (addr->prefix == adv.prefix[i].nd_opt_pi_prefix_len &&
 278                                         !odhcpd_bmemcmp(&adv.prefix[i].nd_opt_pi_prefix,
 279                                         &addr->addr, addr->prefix))
 280                                 p = &adv.prefix[i];
 281                 }
 282
 283                 if (!p) {
 284                         if (cnt >= ARRAY_SIZE(adv.prefix))
 285                                 break;
 286
 287                         p = &adv.prefix[cnt++];
 288                 }
 289
 290                 if (addr->preferred > (uint32_t)now &&
 291                                 minvalid > 1000LL * (addr->valid - now))
 292                         minvalid = 1000LL * (addr->valid - now);
 293
 294                 if (maxvalid < 1000LL * (addr->valid - now))
 295                         maxvalid = 1000LL * (addr->valid - now);
 296
 297                 if (((addr->addr.s6_addr[0] & 0xfe) != 0xfc || iface->default_router)
 298                                 && ntohs(adv.h.nd_ra_router_lifetime) < addr->valid - now)
 299                         adv.h.nd_ra_router_lifetime = htons(addr->valid - now);
 300
 301                 odhcpd_bmemcpy(&p->nd_opt_pi_prefix, &addr->addr,
 302                                 (iface->ra_advrouter) ? 128 : addr->prefix);
 303                 p->nd_opt_pi_type = ND_OPT_PREFIX_INFORMATION;
 304                 p->nd_opt_pi_len = 4;
 305                 p->nd_opt_pi_prefix_len = (addr->prefix < 64) ? 64 : addr->prefix;
 306                 p->nd_opt_pi_flags_reserved = 0;
 307                 if (!iface->ra_not_onlink)
 308                         p->nd_opt_pi_flags_reserved |= ND_OPT_PI_FLAG_ONLINK;
 309                 if (iface->managed < RELAYD_MANAGED_NO_AFLAG && addr->prefix <= 64)
 310                         p->nd_opt_pi_flags_reserved |= ND_OPT_PI_FLAG_AUTO;
 311                 if (iface->ra_advrouter)
 312                         p->nd_opt_pi_flags_reserved |= ND_OPT_PI_FLAG_RADDR;
 313                 p->nd_opt_pi_valid_time = htonl(addr->valid - now);
 314                 if (addr->preferred > (uint32_t)now)
 315                         p->nd_opt_pi_preferred_time = htonl(addr->preferred - now);
 316
 317
 318                 if (addr->preferred - now > dns_time) {
 319                         dns_time = addr->preferred - now;
 320                         dns_pref = addr->addr;
 321                 }
 322         }
 323
 324         if (!iface->default_router && ntohs(adv.h.nd_ra_router_lifetime) == 1) {
 325                 syslog(LOG_WARNING, "A default route is present but there is no public prefix "
 326                                 "on %s thus we don't announce a default route!", iface->ifname);
 327                 adv.h.nd_ra_router_lifetime = 0;
 328         }
 329
 330         // DNS Recursive DNS
 331         if (iface->dns_cnt > 0) {
 332                 dns_addr = iface->dns;
 333                 dns_cnt = iface->dns_cnt;
 334                 dns_time = 0;
 335         }
 336
 337         if (!dns_addr || IN6_IS_ADDR_UNSPECIFIED(dns_addr))
 338                 dns_cnt = 0;
 339
 340         struct {
 341                 uint8_t type;
 342                 uint8_t len;
 343                 uint8_t pad;
 344                 uint8_t pad2;
 345                 uint32_t lifetime;
 346         } dns = {ND_OPT_RECURSIVE_DNS, (1 + (2 * dns_cnt)), 0, 0, htonl(dns_time)};
 347
 348
 349
 350         // DNS Search options
 351         uint8_t search_buf[256], *search_domain = iface->search;
 352         size_t search_len = iface->search_len, search_padded = 0;
 353
 354         if (!search_domain && !res_init() && _res.dnsrch[0] && _res.dnsrch[0][0]) {
 355                 int len = dn_comp(_res.dnsrch[0], search_buf,
 356                                 sizeof(search_buf), NULL, NULL);
 357                 if (len > 0) {
 358                         search_domain = search_buf;
 359                         search_len = len;
 360                 }
 361         }
 362
 363         if (search_len > 0)
 364                 search_padded = ((search_len + 7) & (~7)) + 8;
 365
 366         struct {
 367                 uint8_t type;
 368                 uint8_t len;
 369                 uint8_t pad;
 370                 uint8_t pad2;
 371                 uint32_t lifetime;
 372                 uint8_t name[];
 373         } *search = alloca(sizeof(*search) + search_padded);
 374
 375         search->type = ND_OPT_DNS_SEARCH;
 376         search->len = search_len ? ((sizeof(*search) + search_padded) / 8) : 0;
 377         search->pad = 0;
 378         search->pad2 = 0;
 379         memcpy(search->name, search_domain, search_len);
 380         memset(&search->name[search_len], 0, search_padded - search_len);
 381
 382
 383         size_t routes_cnt = 0;
 384         struct {
 385                 uint8_t type;
 386                 uint8_t len;
 387                 uint8_t prefix;
 388                 uint8_t flags;
 389                 uint32_t lifetime;
 390                 uint32_t addr[4];
 391         } routes[RELAYD_MAX_PREFIXES];
 392
 393         for (ssize_t i = 0; i < ipcnt; ++i) {
 394                 struct odhcpd_ipaddr *addr = &addrs[i];
 395                 if (addr->dprefix > 64 || addr->dprefix == 0 || addr->valid <= (uint32_t)now ||
 396                                 (addr->dprefix == 64 && addr->prefix == 64)) {
 397                         continue; // Address not suitable
 398                 } else if (addr->dprefix > 32) {
 399                         addr->addr.s6_addr32[1] &= htonl(~((1U << (64 - addr->dprefix)) - 1));
 400                 } else if (addr->dprefix <= 32) {
 401                         addr->addr.s6_addr32[0] &= htonl(~((1U << (32 - addr->dprefix)) - 1));
 402                         addr->addr.s6_addr32[1] = 0;
 403                 }
 404
 405                 routes[routes_cnt].type = ND_OPT_ROUTE_INFO;
 406                 routes[routes_cnt].len = sizeof(*routes) / 8;
 407                 routes[routes_cnt].prefix = addr->dprefix;
 408                 routes[routes_cnt].flags = 0;
 409                 if (iface->route_preference < 0)
 410                         routes[routes_cnt].flags |= ND_RA_PREF_LOW;
 411                 else if (iface->route_preference > 0)
 412                         routes[routes_cnt].flags |= ND_RA_PREF_HIGH;
 413                 routes[routes_cnt].lifetime = htonl(addr->valid - now);
 414                 routes[routes_cnt].addr[0] = addr->addr.s6_addr32[0];
 415                 routes[routes_cnt].addr[1] = addr->addr.s6_addr32[1];
 416                 routes[routes_cnt].addr[2] = 0;
 417                 routes[routes_cnt].addr[3] = 0;
 418
 419                 ++routes_cnt;
 420         }
 421
 422         // Calculate periodic transmit
 423         int msecs = 0;
 424         uint32_t maxival = iface->ra_maxinterval * 1000;
 425         uint32_t minival;
 426
 427         if (maxival < 4000 || maxival > MaxRtrAdvInterval * 1000)
 428                 maxival = MaxRtrAdvInterval * 1000;
 429
 430         if (maxival > minvalid / 3) {
 431                 maxival = minvalid / 3;
 432
 433                 if (maxival < 4000)
 434                         maxival = 4000;
 435         }
 436
 437         minival = (maxival * 3) / 4;
 438
 439         search->lifetime = htonl(maxvalid / 1000);
 440
 441         if (!dns.lifetime)
 442                 dns.lifetime = search->lifetime;
 443
 444         odhcpd_urandom(&msecs, sizeof(msecs));
 445         msecs = (labs(msecs) % (maxival - minival)) + minival;
 446
 447         struct icmpv6_opt adv_interval = {
 448                 .type = ND_OPT_RTR_ADV_INTERVAL,
 449                 .len = 1,
 450                 .data = {0, 0, maxival >> 24, maxival >> 16, maxival >> 8, maxival}
 451         };
 452
 453         struct iovec iov[RA_IOV_LEN] = {
 454                         {&adv, (uint8_t*)&adv.prefix[cnt] - (uint8_t*)&adv},
 455                         {&routes, routes_cnt * sizeof(*routes)},
 456                         {&dns, (dns_cnt) ? sizeof(dns) : 0},
 457                         {dns_addr, dns_cnt * sizeof(*dns_addr)},
 458                         {search, search->len * 8},
 459                         {&adv_interval, adv_interval.len * 8}};
 460         struct sockaddr_in6 dest = {AF_INET6, 0, 0, ALL_IPV6_NODES, 0};
 461
 462         if (from && !IN6_IS_ADDR_UNSPECIFIED(from))
 463                 dest.sin6_addr = *from;
 464
 465         odhcpd_send(router_event.uloop.fd,
 466                         &dest, iov, ARRAY_SIZE(iov), iface);
 467
 468         return msecs;
 469 }
 470
 471
 472 static void trigger_router_advert(struct uloop_timeout *event)
 473 {
 474         struct interface *iface = container_of(event, struct interface, timer_rs);
 475         int msecs = send_router_advert(iface, NULL);
 476
 477         // Rearm timer if not shut down
 478         if (event->cb)
 479                 uloop_timeout_set(event, msecs);
 480 }
 481
 482
 483 // Event handler for incoming ICMPv6 packets
 484 static void handle_icmpv6(void *addr, void *data, size_t len,
 485                 struct interface *iface, _unused void *dest)
 486 {
 487         struct icmp6_hdr *hdr = data;
 488         struct sockaddr_in6 *from = addr;
 489
 490         if (!router_icmpv6_valid(addr, data, len))
 491                 return;
 492
 493         if ((iface->ra == RELAYD_SERVER && !iface->master)) { // Server mode
 494                 if (hdr->icmp6_type == ND_ROUTER_SOLICIT)
 495                         send_router_advert(iface, &from->sin6_addr);
 496         } else if (iface->ra == RELAYD_RELAY) { // Relay mode
 497                 if (hdr->icmp6_type == ND_ROUTER_ADVERT && iface->master)
 498                         forward_router_advertisement(data, len);
 499                 else if (hdr->icmp6_type == ND_ROUTER_SOLICIT && !iface->master)
 500                         forward_router_solicitation(odhcpd_get_master_interface());
 501         }
 502 }
 503
 504
 505 // Forward router solicitation
 506 static void forward_router_solicitation(const struct interface *iface)
 507 {
 508         if (!iface)
 509                 return;
 510
 511         struct icmp6_hdr rs = {ND_ROUTER_SOLICIT, 0, 0, {{0}}};
 512         struct iovec iov = {&rs, sizeof(rs)};
 513         struct sockaddr_in6 all_routers =
 514                 {AF_INET6, 0, 0, ALL_IPV6_ROUTERS, iface->ifindex};
 515
 516         syslog(LOG_NOTICE, "Sending RS to %s", iface->ifname);
 517         odhcpd_send(router_event.uloop.fd, &all_routers, &iov, 1, iface);
 518 }
 519
 520
 521 // Handler for incoming router solicitations on slave interfaces
 522 static void forward_router_advertisement(uint8_t *data, size_t len)
 523 {
 524         struct nd_router_advert *adv = (struct nd_router_advert *)data;
 525
 526         // Rewrite options
 527         uint8_t *end = data + len;
 528         uint8_t *mac_ptr = NULL;
 529         struct in6_addr *dns_ptr = NULL;
 530         size_t dns_count = 0;
 531
 532         struct icmpv6_opt *opt;
 533         icmpv6_for_each_option(opt, &adv[1], end) {
 534                 if (opt->type == ND_OPT_SOURCE_LINKADDR) {
 535                         // Store address of source MAC-address
 536                         mac_ptr = opt->data;
 537                 } else if (opt->type == ND_OPT_RECURSIVE_DNS && opt->len > 1) {
 538                         // Check if we have to rewrite DNS
 539                         dns_ptr = (struct in6_addr*)&opt->data[6];
 540                         dns_count = (opt->len - 1) / 2;
 541                 }
 542         }
 543
 544         syslog(LOG_NOTICE, "Got a RA");
 545
 546         // Indicate a proxy, however we don't follow the rest of RFC 4389 yet
 547         adv->nd_ra_flags_reserved |= ND_RA_FLAG_PROXY;
 548
 549         // Forward advertisement to all slave interfaces
 550         struct sockaddr_in6 all_nodes = {AF_INET6, 0, 0, ALL_IPV6_NODES, 0};
 551         struct iovec iov = {data, len};
 552
 553         struct interface *iface;
 554         list_for_each_entry(iface, &interfaces, head) {
 555                 if (iface->ra != RELAYD_RELAY || iface->master)
 556                         continue;
 557
 558                 // Fixup source hardware address option
 559                 if (mac_ptr)
 560                         odhcpd_get_mac(iface, mac_ptr);
 561
 562                 // If we have to rewrite DNS entries
 563                 if (iface->always_rewrite_dns && dns_ptr && dns_count > 0) {
 564                         const struct in6_addr *rewrite = iface->dns;
 565                         struct in6_addr addr;
 566                         size_t rewrite_cnt = iface->dns_cnt;
 567
 568                         if (rewrite_cnt == 0) {
 569                                 if (odhcpd_get_preferred_interface_address(iface->ifindex, &addr) < 1)
 570                                         continue; // Unable to comply
 571
 572                                 rewrite = &addr;
 573                                 rewrite_cnt = 1;
 574                         }
 575
 576                         // Copy over any other addresses
 577                         for (size_t i = 0; i < dns_count; ++i) {
 578                                 size_t j = (i < rewrite_cnt) ? i : rewrite_cnt - 1;
 579                                 dns_ptr[i] = rewrite[j];
 580                         }
 581                 }
 582
 583                 odhcpd_send(router_event.uloop.fd, &all_nodes, &iov, 1, iface);
 584         }
 585 }