nest/neighbor.c

   1 /*
   2  *      BIRD -- Neighbor Cache
   3  *
   4  *      (c) 1998--2000 Martin Mares <mj@ucw.cz>
   5  *
   6  *      Can be freely distributed and used under the terms of the GNU GPL.
   7  */
   8
   9 /**
  10  * DOC: Neighbor cache
  11  *
  12  * Most routing protocols need to associate their internal state data with
  13  * neighboring routers, check whether an address given as the next hop
  14  * attribute of a route is really an address of a directly connected host
  15  * and which interface is it connected through. Also, they often need to
  16  * be notified when a neighbor ceases to exist or when their long awaited
  17  * neighbor becomes connected. The neighbor cache is there to solve all
  18  * these problems.
  19  *
  20  * The neighbor cache maintains a collection of neighbor entries. Each
  21  * entry represents one IP address corresponding to either our directly
  22  * connected neighbor or our own end of the link (when the scope of the
  23  * address is set to %SCOPE_HOST) together with per-neighbor data belonging to a
  24  * single protocol.
  25  *
  26  * Active entries represent known neighbors and are stored in a hash
  27  * table (to allow fast retrieval based on the IP address of the node) and
  28  * two linked lists: one global and one per-interface (allowing quick
  29  * processing of interface change events). Inactive entries exist only
  30  * when the protocol has explicitly requested it via the %NEF_STICKY
  31  * flag because it wishes to be notified when the node will again become
  32  * a neighbor. Such entries are enqueued in a special list which is walked
  33  * whenever an interface changes its state to up.
  34  *
  35  * When a neighbor event occurs (a neighbor gets disconnected or a sticky
  36  * inactive neighbor becomes connected), the protocol hook neigh_notify()
  37  * is called to advertise the change.
  38  */
  39
  40 #undef LOCAL_DEBUG
  41
  42 #include "nest/bird.h"
  43 #include "nest/iface.h"
  44 #include "nest/protocol.h"
  45 #include "lib/resource.h"
  46
  47 #define NEIGH_HASH_SIZE 256
  48
  49 static slab *neigh_slab;
  50 static list sticky_neigh_list, neigh_hash_table[NEIGH_HASH_SIZE];
  51
  52 static inline unsigned int
  53 neigh_hash(struct proto *p, ip_addr *a)
  54 {
  55   return (p->hash_key ^ ipa_hash(*a)) & (NEIGH_HASH_SIZE-1);
  56 }
  57
  58 static int
  59 if_connected(ip_addr *a, struct iface *i) /* -1=error, 1=match, 0=no match */
  60 {
  61   struct ifa *b;
  62
  63   if (!(i->flags & IF_UP))
  64     return -1;
  65   WALK_LIST(b, i->addrs)
  66     {
  67       if (ipa_equal(*a, b->ip))
  68         return SCOPE_HOST;
  69       if (b->flags & IA_PEER)
  70         {
  71           if (ipa_equal(*a, b->opposite))
  72             return b->scope;
  73         }
  74       else
  75         {
  76           if (ipa_in_net(*a, b->prefix, b->pxlen))
  77             {
  78 #ifndef IPV6
  79               if ((b->pxlen < (BITS_PER_IP_ADDRESS - 1)) &&
  80                   (ipa_equal(*a, b->prefix) ||  /* Network address */
  81                    ipa_equal(*a, b->brd)))      /* Broadcast */
  82                 return -1;
  83 #endif
  84
  85               return b->scope;
  86             }
  87         }
  88       }
  89   return -1;
  90 }
  91
  92 /**
  93  * neigh_find - find or create a neighbor entry.
  94  * @p: protocol which asks for the entry.
  95  * @a: pointer to IP address of the node to be searched for.
  96  * @flags: 0 or %NEF_STICKY if you want to create a sticky entry.
  97  *
  98  * Search the neighbor cache for a node with given IP address. If
  99  * it's found, a pointer to the neighbor entry is returned. If no
 100  * such entry exists and the node is directly connected on
 101  * one of our active interfaces, a new entry is created and returned
 102  * to the caller with protocol-dependent fields initialized to zero.
 103  * If the node is not connected directly or *@a is not a valid unicast
 104  * IP address, neigh_find() returns %NULL.
 105  */
 106 neighbor *
 107 neigh_find(struct proto *p, ip_addr *a, unsigned flags)
 108 {
 109   return neigh_find2(p, a, NULL, flags);
 110 }
 111
 112
 113 neighbor *
 114 neigh_find2(struct proto *p, ip_addr *a, struct iface *ifa, unsigned flags)
 115 {
 116   neighbor *n;
 117   int class, scope = -1;
 118   unsigned int h = neigh_hash(p, a);
 119   struct iface *i;
 120
 121   WALK_LIST(n, neigh_hash_table[h])     /* Search the cache */
 122     if (n->proto == p && ipa_equal(*a, n->addr) && (!ifa || (ifa == n->iface)))
 123       return n;
 124
 125   class = ipa_classify(*a);
 126   if (class < 0)                        /* Invalid address */
 127     return NULL;
 128   if (((class & IADDR_SCOPE_MASK) == SCOPE_HOST) ||
 129       (((class & IADDR_SCOPE_MASK) == SCOPE_LINK) && (ifa == NULL)) ||
 130       !(class & IADDR_HOST))
 131     return NULL;                        /* Bad scope or a somecast */
 132
 133   if (ifa)
 134     {
 135       scope = if_connected(a, ifa);
 136       flags |= NEF_BIND;
 137
 138       if ((scope < 0) && (flags & NEF_ONLINK))
 139         scope = class & IADDR_SCOPE_MASK;
 140     }
 141   else
 142     WALK_LIST(i, iface_list)
 143       if ((scope = if_connected(a, i)) >= 0)
 144         {
 145           ifa = i;
 146           break;
 147         }
 148
 149   /* scope < 0 means i don't know neighbor */
 150   /* scope >= 0 implies ifa != NULL */
 151
 152   if ((scope < 0) && !(flags & NEF_STICKY))
 153     return NULL;
 154
 155   n = sl_alloc(neigh_slab);
 156   n->addr = *a;
 157   if (scope >= 0)
 158     {
 159       add_tail(&neigh_hash_table[h], &n->n);
 160       add_tail(&ifa->neighbors, &n->if_n);
 161     }
 162   else
 163     {
 164       add_tail(&sticky_neigh_list, &n->n);
 165       scope = -1;
 166     }
 167   n->iface = ifa;
 168   n->proto = p;
 169   n->data = NULL;
 170   n->aux = 0;
 171   n->flags = flags;
 172   n->scope = scope;
 173   return n;
 174 }
 175
 176 /**
 177  * neigh_dump - dump specified neighbor entry.
 178  * @n: the entry to dump
 179  *
 180  * This functions dumps the contents of a given neighbor entry
 181  * to debug output.
 182  */
 183 void
 184 neigh_dump(neighbor *n)
 185 {
 186   debug("%p %I ", n, n->addr);
 187   if (n->iface)
 188     debug("%s ", n->iface->name);
 189   else
 190     debug("[] ");
 191   debug("%s %p %08x scope %s", n->proto->name, n->data, n->aux, ip_scope_text(n->scope));
 192   if (n->flags & NEF_STICKY)
 193     debug(" STICKY");
 194   debug("\n");
 195 }
 196
 197 /**
 198  * neigh_dump_all - dump all neighbor entries.
 199  *
 200  * This function dumps the contents of the neighbor cache to
 201  * debug output.
 202  */
 203 void
 204 neigh_dump_all(void)
 205 {
 206   neighbor *n;
 207   int i;
 208
 209   debug("Known neighbors:\n");
 210   WALK_LIST(n, sticky_neigh_list)
 211     neigh_dump(n);
 212   for(i=0; i<NEIGH_HASH_SIZE; i++)
 213     WALK_LIST(n, neigh_hash_table[i])
 214       neigh_dump(n);
 215   debug("\n");
 216 }
 217
 218 static void
 219 neigh_up(neighbor *n, struct iface *i, int scope)
 220 {
 221   n->iface = i;
 222   n->scope = scope;
 223   add_tail(&i->neighbors, &n->if_n);
 224   rem_node(&n->n);
 225   add_tail(&neigh_hash_table[neigh_hash(n->proto, &n->addr)], &n->n);
 226   DBG("Waking up sticky neighbor %I\n", n->addr);
 227   if (n->proto->neigh_notify && n->proto->core_state != FS_FLUSHING)
 228     n->proto->neigh_notify(n);
 229 }
 230
 231 static void
 232 neigh_down(neighbor *n)
 233 {
 234   DBG("Flushing neighbor %I on %s\n", n->addr, n->iface->name);
 235   rem_node(&n->if_n);
 236   if (! (n->flags & NEF_BIND))
 237     n->iface = NULL;
 238   n->scope = -1;
 239   if (n->proto->neigh_notify && n->proto->core_state != FS_FLUSHING)
 240     n->proto->neigh_notify(n);
 241   rem_node(&n->n);
 242   if (n->flags & NEF_STICKY)
 243     {
 244       add_tail(&sticky_neigh_list, &n->n);
 245
 246       /* Respawn neighbor if there is another matching prefix */
 247       struct iface *i;
 248       int scope;
 249
 250       if (!n->iface)
 251         WALK_LIST(i, iface_list)
 252           if ((scope = if_connected(&n->addr, i)) >= 0)
 253             {
 254               neigh_up(n, i, scope);
 255               return;
 256             }
 257     }
 258   else
 259     sl_free(neigh_slab, n);
 260 }
 261
 262
 263 /**
 264  * neigh_if_up: notify neighbor cache about interface up event
 265  * @i: interface in question
 266  *
 267  * Tell the neighbor cache that a new interface became up.
 268  *
 269  * The neighbor cache wakes up all inactive sticky neighbors with
 270  * addresses belonging to prefixes of the interface @i.
 271  */
 272 void
 273 neigh_if_up(struct iface *i)
 274 {
 275   neighbor *n, *next;
 276   int scope;
 277
 278   WALK_LIST_DELSAFE(n, next, sticky_neigh_list)
 279     if ((!n->iface || n->iface == i) &&
 280         ((scope = if_connected(&n->addr, i)) >= 0))
 281       neigh_up(n, i, scope);
 282 }
 283
 284 /**
 285  * neigh_if_down - notify neighbor cache about interface down event
 286  * @i: the interface in question
 287  *
 288  * Notify the neighbor cache that an interface has ceased to exist.
 289  *
 290  * It causes all entries belonging to neighbors connected to this interface
 291  * to be flushed.
 292  */
 293 void
 294 neigh_if_down(struct iface *i)
 295 {
 296   node *x, *y;
 297
 298   WALK_LIST_DELSAFE(x, y, i->neighbors)
 299     neigh_down(SKIP_BACK(neighbor, if_n, x));
 300 }
 301
 302 /**
 303  * neigh_if_link - notify neighbor cache about interface link change
 304  * @i: the interface in question
 305  *
 306  * Notify the neighbor cache that an interface changed link state.
 307  * All owners of neighbor entries connected to this interface are
 308  * notified.
 309  */
 310 void
 311 neigh_if_link(struct iface *i)
 312 {
 313   node *x, *y;
 314
 315   WALK_LIST_DELSAFE(x, y, i->neighbors)
 316     {
 317       neighbor *n = SKIP_BACK(neighbor, if_n, x);
 318       if (n->proto->neigh_notify && n->proto->core_state != FS_FLUSHING)
 319         n->proto->neigh_notify(n);
 320     }
 321 }
 322
 323 /**
 324  * neigh_ifa_update: notify neighbor cache about interface address add or remove event
 325  * @ifa: interface address in question
 326  *
 327  * Tell the neighbor cache that an address was added or removed.
 328  *
 329  * The neighbor cache wakes up all inactive sticky neighbors with
 330  * addresses belonging to prefixes of the interface belonging to @ifa
 331  * and causes all unreachable neighbors to be flushed.
 332  */
 333 void
 334 neigh_ifa_update(struct ifa *a)
 335 {
 336   struct iface *i = a->iface;
 337   node *x, *y;
 338
 339   /* Remove all neighbors whose scope has changed */
 340   WALK_LIST_DELSAFE(x, y, i->neighbors)
 341     {
 342       neighbor *n = SKIP_BACK(neighbor, if_n, x);
 343       if (if_connected(&n->addr, i) != n->scope)
 344         neigh_down(n);
 345     }
 346
 347   /* Wake up all sticky neighbors that are reachable now */
 348   neigh_if_up(i);
 349 }
 350
 351 static inline void
 352 neigh_prune_one(neighbor *n)
 353 {
 354   if (n->proto->proto_state != PS_DOWN)
 355     return;
 356   rem_node(&n->n);
 357   if (n->scope >= 0)
 358     rem_node(&n->if_n);
 359   sl_free(neigh_slab, n);
 360 }
 361
 362 /**
 363  * neigh_prune - prune neighbor cache
 364  *
 365  * neigh_prune() examines all neighbor entries cached and removes those
 366  * corresponding to inactive protocols. It's called whenever a protocol
 367  * is shut down to get rid of all its heritage.
 368  */
 369 void
 370 neigh_prune(void)
 371 {
 372   neighbor *n;
 373   node *m;
 374   int i;
 375
 376   DBG("Pruning neighbors\n");
 377   for(i=0; i<NEIGH_HASH_SIZE; i++)
 378     WALK_LIST_DELSAFE(n, m, neigh_hash_table[i])
 379       neigh_prune_one(n);
 380   WALK_LIST_DELSAFE(n, m, sticky_neigh_list)
 381     neigh_prune_one(n);
 382 }
 383
 384 /**
 385  * neigh_init - initialize the neighbor cache.
 386  * @if_pool: resource pool to be used for neighbor entries.
 387  *
 388  * This function is called during BIRD startup to initialize
 389  * the neighbor cache module.
 390  */
 391 void
 392 neigh_init(pool *if_pool)
 393 {
 394   int i;
 395
 396   neigh_slab = sl_new(if_pool, sizeof(neighbor));
 397   init_list(&sticky_neigh_list);
 398   for(i=0; i<NEIGH_HASH_SIZE; i++)
 399     init_list(&neigh_hash_table[i]);
 400 }