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_UNNUMBERED)
  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
 107
 108 neighbor *
 109 neigh_find(struct proto *p, ip_addr *a, unsigned flags)
 110 {
 111   return neigh_find2(p, a, NULL, flags);
 112 }
 113
 114
 115 neighbor *
 116 neigh_find2(struct proto *p, ip_addr *a, struct iface *ifa, unsigned flags)
 117 {
 118   neighbor *n;
 119   int class, scope = -1;       ;
 120   unsigned int h = neigh_hash(p, a);
 121   struct iface *i;
 122
 123   WALK_LIST(n, neigh_hash_table[h])     /* Search the cache */
 124     if (n->proto == p && ipa_equal(*a, n->addr) && (!ifa || (ifa == n->iface)))
 125       return n;
 126
 127   class = ipa_classify(*a);
 128   if (class < 0)                        /* Invalid address */
 129     return NULL;
 130   if (((class & IADDR_SCOPE_MASK) == SCOPE_HOST) ||
 131       (((class & IADDR_SCOPE_MASK) == SCOPE_LINK) && (ifa == NULL)) ||
 132       !(class & IADDR_HOST))
 133     return NULL;                        /* Bad scope or a somecast */
 134
 135   if (ifa)
 136     {
 137       scope = if_connected(a, ifa);
 138
 139       if ((scope < 0) && (flags & NEF_ONLINK))
 140         scope = class & IADDR_SCOPE_MASK;
 141     }
 142   else
 143     WALK_LIST(i, iface_list)
 144       if ((scope = if_connected(a, i)) >= 0)
 145         {
 146           ifa = i;
 147           break;
 148         }
 149
 150   /* scope < 0 means i don't know neighbor */
 151   /* scope >= 0 implies ifa != NULL */
 152
 153   if ((scope < 0) && !(flags & NEF_STICKY))
 154     return NULL;
 155
 156   n = sl_alloc(neigh_slab);
 157   n->addr = *a;
 158   if (scope >= 0)
 159     {
 160       add_tail(&neigh_hash_table[h], &n->n);
 161       add_tail(&ifa->neighbors, &n->if_n);
 162     }
 163   else
 164     {
 165       /* sticky flag does not work for link-local neighbors;
 166          fortunately, we don't use this combination */
 167       add_tail(&sticky_neigh_list, &n->n);
 168       ifa = NULL;
 169       scope = 0;
 170     }
 171   n->iface = ifa;
 172   n->proto = p;
 173   n->data = NULL;
 174   n->aux = 0;
 175   n->flags = flags;
 176   n->scope = scope;
 177   return n;
 178 }
 179
 180 /**
 181  * neigh_dump - dump specified neighbor entry.
 182  * @n: the entry to dump
 183  *
 184  * This functions dumps the contents of a given neighbor entry
 185  * to debug output.
 186  */
 187 void
 188 neigh_dump(neighbor *n)
 189 {
 190   debug("%p %I ", n, n->addr);
 191   if (n->iface)
 192     debug("%s ", n->iface->name);
 193   else
 194     debug("[] ");
 195   debug("%s %p %08x scope %s", n->proto->name, n->data, n->aux, ip_scope_text(n->scope));
 196   if (n->flags & NEF_STICKY)
 197     debug(" STICKY");
 198   debug("\n");
 199 }
 200
 201 /**
 202  * neigh_dump_all - dump all neighbor entries.
 203  *
 204  * This function dumps the contents of the neighbor cache to
 205  * debug output.
 206  */
 207 void
 208 neigh_dump_all(void)
 209 {
 210   neighbor *n;
 211   int i;
 212
 213   debug("Known neighbors:\n");
 214   WALK_LIST(n, sticky_neigh_list)
 215     neigh_dump(n);
 216   for(i=0; i<NEIGH_HASH_SIZE; i++)
 217     WALK_LIST(n, neigh_hash_table[i])
 218       neigh_dump(n);
 219   debug("\n");
 220 }
 221
 222 /**
 223  * neigh_if_up: notify neighbor cache about interface up event
 224  * @i: interface in question
 225  *
 226  * Tell the neighbor cache that a new interface became up.
 227  *
 228  * The neighbor cache wakes up all inactive sticky neighbors with
 229  * addresses belonging to prefixes of the interface @i.
 230  */
 231 void
 232 neigh_if_up(struct iface *i)
 233 {
 234   neighbor *n, *next;
 235   int scope;
 236
 237   WALK_LIST_DELSAFE(n, next, sticky_neigh_list)
 238     if ((scope = if_connected(&n->addr, i)) >= 0)
 239       {
 240         n->iface = i;
 241         n->scope = scope;
 242         add_tail(&i->neighbors, &n->if_n);
 243         rem_node(&n->n);
 244         add_tail(&neigh_hash_table[neigh_hash(n->proto, &n->addr)], &n->n);
 245         DBG("Waking up sticky neighbor %I\n", n->addr);
 246         if (n->proto->neigh_notify && n->proto->core_state != FS_FLUSHING)
 247           n->proto->neigh_notify(n);
 248       }
 249 }
 250
 251 /**
 252  * neigh_if_down - notify neighbor cache about interface down event
 253  * @i: the interface in question
 254  *
 255  * Notify the neighbor cache that an interface has ceased to exist.
 256  *
 257  * It causes all entries belonging to neighbors connected to this interface
 258  * to be flushed.
 259  */
 260 void
 261 neigh_if_down(struct iface *i)
 262 {
 263   node *x, *y;
 264
 265   WALK_LIST_DELSAFE(x, y, i->neighbors)
 266     {
 267       neighbor *n = SKIP_BACK(neighbor, if_n, x);
 268       DBG("Flushing neighbor %I on %s\n", n->addr, i->name);
 269       rem_node(&n->if_n);
 270       n->iface = NULL;
 271       if (n->proto->neigh_notify && n->proto->core_state != FS_FLUSHING)
 272         n->proto->neigh_notify(n);
 273       rem_node(&n->n);
 274       if (n->flags & NEF_STICKY)
 275         add_tail(&sticky_neigh_list, &n->n);
 276       else
 277         sl_free(neigh_slab, n);
 278     }
 279 }
 280
 281 static inline void
 282 neigh_prune_one(neighbor *n)
 283 {
 284   if (n->proto->proto_state != PS_DOWN)
 285     return;
 286   rem_node(&n->n);
 287   if (n->iface)
 288     rem_node(&n->if_n);
 289   sl_free(neigh_slab, n);
 290 }
 291
 292 /**
 293  * neigh_prune - prune neighbor cache
 294  *
 295  * neigh_prune() examines all neighbor entries cached and removes those
 296  * corresponding to inactive protocols. It's called whenever a protocol
 297  * is shut down to get rid of all its heritage.
 298  */
 299 void
 300 neigh_prune(void)
 301 {
 302   neighbor *n;
 303   node *m;
 304   int i;
 305
 306   DBG("Pruning neighbors\n");
 307   for(i=0; i<NEIGH_HASH_SIZE; i++)
 308     WALK_LIST_DELSAFE(n, m, neigh_hash_table[i])
 309       neigh_prune_one(n);
 310   WALK_LIST_DELSAFE(n, m, sticky_neigh_list)
 311     neigh_prune_one(n);
 312 }
 313
 314 /**
 315  * neigh_init - initialize the neighbor cache.
 316  * @if_pool: resource pool to be used for neighbor entries.
 317  *
 318  * This function is called during BIRD startup to initialize
 319  * the neighbor cache module.
 320  */
 321 void
 322 neigh_init(pool *if_pool)
 323 {
 324   int i;
 325
 326   neigh_slab = sl_new(if_pool, sizeof(neighbor));
 327   init_list(&sticky_neigh_list);
 328   for(i=0; i<NEIGH_HASH_SIZE; i++)
 329     init_list(&neigh_hash_table[i]);
 330 }