ospfd/ospf_ism.c

   1 /*
   2  * OSPF version 2  Interface State Machine
   3  *   From RFC2328 [OSPF Version 2]
   4  * Copyright (C) 1999, 2000 Toshiaki Takada
   5  *
   6  * This file is part of GNU Zebra.
   7  *
   8  * GNU Zebra is free software; you can redistribute it and/or modify it
   9  * under the terms of the GNU General Public License as published by the
  10  * Free Software Foundation; either version 2, or (at your option) any
  11  * later version.
  12  *
  13  * GNU Zebra is distributed in the hope that it will be useful, but
  14  * WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License along
  19  * with this program; see the file COPYING; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #include <zebra.h>
  24
  25 #include "thread.h"
  26 #include "linklist.h"
  27 #include "prefix.h"
  28 #include "if.h"
  29 #include "table.h"
  30 #include "log.h"
  31
  32 #include "ospfd/ospfd.h"
  33 #include "ospfd/ospf_interface.h"
  34 #include "ospfd/ospf_ism.h"
  35 #include "ospfd/ospf_asbr.h"
  36 #include "ospfd/ospf_lsa.h"
  37 #include "ospfd/ospf_lsdb.h"
  38 #include "ospfd/ospf_neighbor.h"
  39 #include "ospfd/ospf_nsm.h"
  40 #include "ospfd/ospf_network.h"
  41 #include "ospfd/ospf_dump.h"
  42 #include "ospfd/ospf_packet.h"
  43 #include "ospfd/ospf_flood.h"
  44 #include "ospfd/ospf_abr.h"
  45
  46 DEFINE_HOOK(ospf_ism_change,
  47             (struct ospf_interface * oi, int state, int oldstate),
  48             (oi, state, oldstate));
  49
  50 /* elect DR and BDR. Refer to RFC2319 section 9.4 */
  51 static struct ospf_neighbor *ospf_dr_election_sub(struct list *routers)
  52 {
  53         struct listnode *node;
  54         struct ospf_neighbor *nbr, *max = NULL;
  55
  56         /* Choose highest router priority.
  57            In case of tie, choose highest Router ID. */
  58         for (ALL_LIST_ELEMENTS_RO(routers, node, nbr)) {
  59                 if (max == NULL)
  60                         max = nbr;
  61                 else {
  62                         if (max->priority < nbr->priority)
  63                                 max = nbr;
  64                         else if (max->priority == nbr->priority)
  65                                 if (IPV4_ADDR_CMP(&max->router_id,
  66                                                   &nbr->router_id)
  67                                     < 0)
  68                                         max = nbr;
  69                 }
  70         }
  71
  72         return max;
  73 }
  74
  75 static struct ospf_neighbor *ospf_elect_dr(struct ospf_interface *oi,
  76                                            struct list *el_list)
  77 {
  78         struct list *dr_list;
  79         struct listnode *node;
  80         struct ospf_neighbor *nbr, *dr = NULL, *bdr = NULL;
  81
  82         dr_list = list_new();
  83
  84         /* Add neighbors to the list. */
  85         for (ALL_LIST_ELEMENTS_RO(el_list, node, nbr)) {
  86                 /* neighbor declared to be DR. */
  87                 if (NBR_IS_DR(nbr))
  88                         listnode_add(dr_list, nbr);
  89
  90                 /* Preserve neighbor BDR. */
  91                 if (IPV4_ADDR_SAME(&BDR(oi), &nbr->address.u.prefix4))
  92                         bdr = nbr;
  93         }
  94
  95         /* Elect Designated Router. */
  96         if (listcount(dr_list) > 0)
  97                 dr = ospf_dr_election_sub(dr_list);
  98         else
  99                 dr = bdr;
 100
 101         /* Set DR to interface. */
 102         if (dr)
 103                 DR(oi) = dr->address.u.prefix4;
 104         else
 105                 DR(oi).s_addr = 0;
 106
 107         list_delete(&dr_list);
 108
 109         return dr;
 110 }
 111
 112 static struct ospf_neighbor *ospf_elect_bdr(struct ospf_interface *oi,
 113                                             struct list *el_list)
 114 {
 115         struct list *bdr_list, *no_dr_list;
 116         struct listnode *node;
 117         struct ospf_neighbor *nbr, *bdr = NULL;
 118
 119         bdr_list = list_new();
 120         no_dr_list = list_new();
 121
 122         /* Add neighbors to the list. */
 123         for (ALL_LIST_ELEMENTS_RO(el_list, node, nbr)) {
 124                 /* neighbor declared to be DR. */
 125                 if (NBR_IS_DR(nbr))
 126                         continue;
 127
 128                 /* neighbor declared to be BDR. */
 129                 if (NBR_IS_BDR(nbr))
 130                         listnode_add(bdr_list, nbr);
 131
 132                 listnode_add(no_dr_list, nbr);
 133         }
 134
 135         /* Elect Backup Designated Router. */
 136         if (listcount(bdr_list) > 0)
 137                 bdr = ospf_dr_election_sub(bdr_list);
 138         else
 139                 bdr = ospf_dr_election_sub(no_dr_list);
 140
 141         /* Set BDR to interface. */
 142         if (bdr)
 143                 BDR(oi) = bdr->address.u.prefix4;
 144         else
 145                 BDR(oi).s_addr = 0;
 146
 147         list_delete(&bdr_list);
 148         list_delete(&no_dr_list);
 149
 150         return bdr;
 151 }
 152
 153 static int ospf_ism_state(struct ospf_interface *oi)
 154 {
 155         if (IPV4_ADDR_SAME(&DR(oi), &oi->address->u.prefix4))
 156                 return ISM_DR;
 157         else if (IPV4_ADDR_SAME(&BDR(oi), &oi->address->u.prefix4))
 158                 return ISM_Backup;
 159         else
 160                 return ISM_DROther;
 161 }
 162
 163 static void ospf_dr_eligible_routers(struct route_table *nbrs,
 164                                      struct list *el_list)
 165 {
 166         struct route_node *rn;
 167         struct ospf_neighbor *nbr;
 168
 169         for (rn = route_top(nbrs); rn; rn = route_next(rn))
 170                 if ((nbr = rn->info) != NULL)
 171                         /* Ignore 0.0.0.0 node*/
 172                         if (nbr->router_id.s_addr != INADDR_ANY)
 173                                 /* Is neighbor eligible? */
 174                                 if (nbr->priority > 0)
 175                                         /* Is neighbor upper 2-Way? */
 176                                         if (nbr->state >= NSM_TwoWay)
 177                                                 listnode_add(el_list, nbr);
 178 }
 179
 180 /* Generate AdjOK? NSM event. */
 181 static void ospf_dr_change(struct ospf *ospf, struct route_table *nbrs)
 182 {
 183         struct route_node *rn;
 184         struct ospf_neighbor *nbr;
 185
 186         for (rn = route_top(nbrs); rn; rn = route_next(rn)) {
 187                 nbr = rn->info;
 188
 189                 if (!nbr)
 190                         continue;
 191
 192                 /*
 193                  * Ignore 0.0.0.0 node
 194                  * Is neighbor 2-Way?
 195                  * Ignore myself
 196                  */
 197                 if (nbr->router_id.s_addr != INADDR_ANY
 198                     && nbr->state >= NSM_TwoWay
 199                     && !IPV4_ADDR_SAME(&nbr->router_id, &ospf->router_id))
 200                         OSPF_NSM_EVENT_SCHEDULE(nbr, NSM_AdjOK);
 201         }
 202 }
 203
 204 int ospf_dr_election(struct ospf_interface *oi)
 205 {
 206         struct in_addr old_dr, old_bdr;
 207         int old_state, new_state;
 208         struct list *el_list;
 209
 210         /* backup current values. */
 211         old_dr = DR(oi);
 212         old_bdr = BDR(oi);
 213         old_state = oi->state;
 214
 215         el_list = list_new();
 216
 217         /* List eligible routers. */
 218         ospf_dr_eligible_routers(oi->nbrs, el_list);
 219
 220         /* First election of DR and BDR. */
 221         ospf_elect_bdr(oi, el_list);
 222         ospf_elect_dr(oi, el_list);
 223
 224         new_state = ospf_ism_state(oi);
 225
 226         zlog_debug("DR-Election[1st]: Backup %pI4", &BDR(oi));
 227         zlog_debug("DR-Election[1st]: DR     %pI4", &DR(oi));
 228
 229         if (new_state != old_state
 230             && !(new_state == ISM_DROther && old_state < ISM_DROther)) {
 231                 ospf_elect_bdr(oi, el_list);
 232                 ospf_elect_dr(oi, el_list);
 233
 234                 new_state = ospf_ism_state(oi);
 235
 236                 zlog_debug("DR-Election[2nd]: Backup %pI4", &BDR(oi));
 237                 zlog_debug("DR-Election[2nd]: DR     %pI4", &DR(oi));
 238         }
 239
 240         list_delete(&el_list);
 241
 242         /* if DR or BDR changes, cause AdjOK? neighbor event. */
 243         if (!IPV4_ADDR_SAME(&old_dr, &DR(oi))
 244             || !IPV4_ADDR_SAME(&old_bdr, &BDR(oi)))
 245                 ospf_dr_change(oi->ospf, oi->nbrs);
 246
 247         return new_state;
 248 }
 249
 250
 251 void ospf_hello_timer(struct thread *thread)
 252 {
 253         struct ospf_interface *oi;
 254
 255         oi = THREAD_ARG(thread);
 256         oi->t_hello = NULL;
 257
 258         if (IS_DEBUG_OSPF(ism, ISM_TIMERS))
 259                 zlog_debug("ISM[%s]: Timer (Hello timer expire)", IF_NAME(oi));
 260
 261         /* Sending hello packet. */
 262         ospf_hello_send(oi);
 263
 264         /* Hello timer set. */
 265         OSPF_HELLO_TIMER_ON(oi);
 266 }
 267
 268 static void ospf_wait_timer(struct thread *thread)
 269 {
 270         struct ospf_interface *oi;
 271
 272         oi = THREAD_ARG(thread);
 273         oi->t_wait = NULL;
 274
 275         if (IS_DEBUG_OSPF(ism, ISM_TIMERS))
 276                 zlog_debug("ISM[%s]: Timer (Wait timer expire)", IF_NAME(oi));
 277
 278         OSPF_ISM_EVENT_SCHEDULE(oi, ISM_WaitTimer);
 279 }
 280
 281 /* Hook function called after ospf ISM event is occurred. And vty's
 282    network command invoke this function after making interface
 283    structure. */
 284 static void ism_timer_set(struct ospf_interface *oi)
 285 {
 286         switch (oi->state) {
 287         case ISM_Down:
 288                 /* First entry point of ospf interface state machine. In this
 289                    state
 290                    interface parameters must be set to initial values, and
 291                    timers are
 292                    reset also. */
 293                 OSPF_ISM_TIMER_OFF(oi->t_hello);
 294                 OSPF_ISM_TIMER_OFF(oi->t_wait);
 295                 OSPF_ISM_TIMER_OFF(oi->t_ls_ack);
 296                 break;
 297         case ISM_Loopback:
 298                 /* In this state, the interface may be looped back and will be
 299                    unavailable for regular data traffic. */
 300                 OSPF_ISM_TIMER_OFF(oi->t_hello);
 301                 OSPF_ISM_TIMER_OFF(oi->t_wait);
 302                 OSPF_ISM_TIMER_OFF(oi->t_ls_ack);
 303                 break;
 304         case ISM_Waiting:
 305                 /* The router is trying to determine the identity of DRouter and
 306                    BDRouter. The router begin to receive and send Hello Packets.
 307                    */
 308                 /* send first hello immediately */
 309                 OSPF_ISM_TIMER_MSEC_ON(oi->t_hello, ospf_hello_timer, 1);
 310                 OSPF_ISM_TIMER_ON(oi->t_wait, ospf_wait_timer,
 311                                   OSPF_IF_PARAM(oi, v_wait));
 312                 OSPF_ISM_TIMER_OFF(oi->t_ls_ack);
 313                 break;
 314         case ISM_PointToPoint:
 315                 /* The interface connects to a physical Point-to-point network
 316                    or
 317                    virtual link. The router attempts to form an adjacency with
 318                    neighboring router. Hello packets are also sent. */
 319                 /* send first hello immediately */
 320                 OSPF_ISM_TIMER_MSEC_ON(oi->t_hello, ospf_hello_timer, 1);
 321                 OSPF_ISM_TIMER_OFF(oi->t_wait);
 322                 OSPF_ISM_TIMER_ON(oi->t_ls_ack, ospf_ls_ack_timer,
 323                                   oi->v_ls_ack);
 324                 break;
 325         case ISM_DROther:
 326                 /* The network type of the interface is broadcast or NBMA
 327                    network,
 328                    and the router itself is neither Designated Router nor
 329                    Backup Designated Router. */
 330                 OSPF_HELLO_TIMER_ON(oi);
 331                 OSPF_ISM_TIMER_OFF(oi->t_wait);
 332                 OSPF_ISM_TIMER_ON(oi->t_ls_ack, ospf_ls_ack_timer,
 333                                   oi->v_ls_ack);
 334                 break;
 335         case ISM_Backup:
 336                 /* The network type of the interface is broadcast os NBMA
 337                    network,
 338                    and the router is Backup Designated Router. */
 339                 OSPF_HELLO_TIMER_ON(oi);
 340                 OSPF_ISM_TIMER_OFF(oi->t_wait);
 341                 OSPF_ISM_TIMER_ON(oi->t_ls_ack, ospf_ls_ack_timer,
 342                                   oi->v_ls_ack);
 343                 break;
 344         case ISM_DR:
 345                 /* The network type of the interface is broadcast or NBMA
 346                    network,
 347                    and the router is Designated Router. */
 348                 OSPF_HELLO_TIMER_ON(oi);
 349                 OSPF_ISM_TIMER_OFF(oi->t_wait);
 350                 OSPF_ISM_TIMER_ON(oi->t_ls_ack, ospf_ls_ack_timer,
 351                                   oi->v_ls_ack);
 352                 break;
 353         }
 354 }
 355
 356 static int ism_interface_up(struct ospf_interface *oi)
 357 {
 358         int next_state = 0;
 359
 360         /* if network type is point-to-point, Point-to-MultiPoint or virtual
 361            link,
 362            the state transitions to Point-to-Point. */
 363         if (oi->type == OSPF_IFTYPE_POINTOPOINT
 364             || oi->type == OSPF_IFTYPE_POINTOMULTIPOINT
 365             || oi->type == OSPF_IFTYPE_VIRTUALLINK)
 366                 next_state = ISM_PointToPoint;
 367         /* Else if the router is not eligible to DR, the state transitions to
 368            DROther. */
 369         else if (PRIORITY(oi) == 0) /* router is eligible? */
 370                 next_state = ISM_DROther;
 371         else
 372                 /* Otherwise, the state transitions to Waiting. */
 373                 next_state = ISM_Waiting;
 374
 375         if (oi->type == OSPF_IFTYPE_NBMA)
 376                 ospf_nbr_nbma_if_update(oi->ospf, oi);
 377
 378         /*  ospf_ism_event (t); */
 379         return next_state;
 380 }
 381
 382 static int ism_loop_ind(struct ospf_interface *oi)
 383 {
 384         /* call ism_interface_down. */
 385         /* ret = ism_interface_down (oi); */
 386
 387         return 0;
 388 }
 389
 390 /* Interface down event handler. */
 391 static int ism_interface_down(struct ospf_interface *oi)
 392 {
 393         ospf_if_cleanup(oi);
 394         return 0;
 395 }
 396
 397
 398 static int ism_backup_seen(struct ospf_interface *oi)
 399 {
 400         return ospf_dr_election(oi);
 401 }
 402
 403 static int ism_wait_timer(struct ospf_interface *oi)
 404 {
 405         return ospf_dr_election(oi);
 406 }
 407
 408 static int ism_neighbor_change(struct ospf_interface *oi)
 409 {
 410         return ospf_dr_election(oi);
 411 }
 412
 413 static int ism_ignore(struct ospf_interface *oi)
 414 {
 415         if (IS_DEBUG_OSPF(ism, ISM_EVENTS))
 416                 zlog_debug("ISM[%s]: ism_ignore called", IF_NAME(oi));
 417
 418         return 0;
 419 }
 420
 421 /* Interface State Machine */
 422 const struct {
 423         int (*func)(struct ospf_interface *);
 424         int next_state;
 425 } ISM[OSPF_ISM_STATE_MAX][OSPF_ISM_EVENT_MAX] = {
 426         {
 427                 /* DependUpon: dummy state. */
 428                 {ism_ignore, ISM_DependUpon}, /* NoEvent        */
 429                 {ism_ignore, ISM_DependUpon}, /* InterfaceUp    */
 430                 {ism_ignore, ISM_DependUpon}, /* WaitTimer      */
 431                 {ism_ignore, ISM_DependUpon}, /* BackupSeen     */
 432                 {ism_ignore, ISM_DependUpon}, /* NeighborChange */
 433                 {ism_ignore, ISM_DependUpon}, /* LoopInd        */
 434                 {ism_ignore, ISM_DependUpon}, /* UnloopInd      */
 435                 {ism_ignore, ISM_DependUpon}, /* InterfaceDown  */
 436         },
 437         {
 438                 /* Down:*/
 439                 {ism_ignore, ISM_DependUpon},       /* NoEvent        */
 440                 {ism_interface_up, ISM_DependUpon}, /* InterfaceUp    */
 441                 {ism_ignore, ISM_Down},             /* WaitTimer      */
 442                 {ism_ignore, ISM_Down},             /* BackupSeen     */
 443                 {ism_ignore, ISM_Down},             /* NeighborChange */
 444                 {ism_loop_ind, ISM_Loopback},       /* LoopInd        */
 445                 {ism_ignore, ISM_Down},             /* UnloopInd      */
 446                 {ism_interface_down, ISM_Down},     /* InterfaceDown  */
 447         },
 448         {
 449                 /* Loopback: */
 450                 {ism_ignore, ISM_DependUpon},   /* NoEvent        */
 451                 {ism_ignore, ISM_Loopback},     /* InterfaceUp    */
 452                 {ism_ignore, ISM_Loopback},     /* WaitTimer      */
 453                 {ism_ignore, ISM_Loopback},     /* BackupSeen     */
 454                 {ism_ignore, ISM_Loopback},     /* NeighborChange */
 455                 {ism_ignore, ISM_Loopback},     /* LoopInd        */
 456                 {ism_ignore, ISM_Down},         /* UnloopInd      */
 457                 {ism_interface_down, ISM_Down}, /* InterfaceDown  */
 458         },
 459         {
 460                 /* Waiting: */
 461                 {ism_ignore, ISM_DependUpon},      /* NoEvent        */
 462                 {ism_ignore, ISM_Waiting},       /* InterfaceUp    */
 463                 {ism_wait_timer, ISM_DependUpon},  /* WaitTimer      */
 464                 {ism_backup_seen, ISM_DependUpon}, /* BackupSeen     */
 465                 {ism_ignore, ISM_Waiting},       /* NeighborChange */
 466                 {ism_loop_ind, ISM_Loopback},      /* LoopInd        */
 467                 {ism_ignore, ISM_Waiting},       /* UnloopInd      */
 468                 {ism_interface_down, ISM_Down},    /* InterfaceDown  */
 469         },
 470         {
 471                 /* Point-to-Point: */
 472                 {ism_ignore, ISM_DependUpon},   /* NoEvent        */
 473                 {ism_ignore, ISM_PointToPoint}, /* InterfaceUp    */
 474                 {ism_ignore, ISM_PointToPoint}, /* WaitTimer      */
 475                 {ism_ignore, ISM_PointToPoint}, /* BackupSeen     */
 476                 {ism_ignore, ISM_PointToPoint}, /* NeighborChange */
 477                 {ism_loop_ind, ISM_Loopback},   /* LoopInd        */
 478                 {ism_ignore, ISM_PointToPoint}, /* UnloopInd      */
 479                 {ism_interface_down, ISM_Down}, /* InterfaceDown  */
 480         },
 481         {
 482                 /* DROther: */
 483                 {ism_ignore, ISM_DependUpon},     /* NoEvent        */
 484                 {ism_ignore, ISM_DROther},           /* InterfaceUp    */
 485                 {ism_ignore, ISM_DROther},           /* WaitTimer      */
 486                 {ism_ignore, ISM_DROther},           /* BackupSeen     */
 487                 {ism_neighbor_change, ISM_DependUpon}, /* NeighborChange */
 488                 {ism_loop_ind, ISM_Loopback},     /* LoopInd        */
 489                 {ism_ignore, ISM_DROther},           /* UnloopInd      */
 490                 {ism_interface_down, ISM_Down}, /* InterfaceDown  */
 491         },
 492         {
 493                 /* Backup: */
 494                 {ism_ignore, ISM_DependUpon},     /* NoEvent        */
 495                 {ism_ignore, ISM_Backup},             /* InterfaceUp    */
 496                 {ism_ignore, ISM_Backup},             /* WaitTimer      */
 497                 {ism_ignore, ISM_Backup},             /* BackupSeen     */
 498                 {ism_neighbor_change, ISM_DependUpon}, /* NeighborChange */
 499                 {ism_loop_ind, ISM_Loopback},     /* LoopInd        */
 500                 {ism_ignore, ISM_Backup},             /* UnloopInd      */
 501                 {ism_interface_down, ISM_Down}, /* InterfaceDown  */
 502         },
 503         {
 504                 /* DR: */
 505                 {ism_ignore, ISM_DependUpon},     /* NoEvent        */
 506                 {ism_ignore, ISM_DR},                  /* InterfaceUp    */
 507                 {ism_ignore, ISM_DR},                  /* WaitTimer      */
 508                 {ism_ignore, ISM_DR},                  /* BackupSeen     */
 509                 {ism_neighbor_change, ISM_DependUpon}, /* NeighborChange */
 510                 {ism_loop_ind, ISM_Loopback},     /* LoopInd        */
 511                 {ism_ignore, ISM_DR},                  /* UnloopInd      */
 512                 {ism_interface_down, ISM_Down}, /* InterfaceDown  */
 513         },
 514 };
 515
 516 static const char *const ospf_ism_event_str[] = {
 517         "NoEvent",      "InterfaceUp", "WaitTimer", "BackupSeen",
 518         "NeighborChange", "LoopInd",     "UnLoopInd", "InterfaceDown",
 519 };
 520
 521 static void ism_change_state(struct ospf_interface *oi, int state)
 522 {
 523         int old_state;
 524         struct ospf_lsa *lsa;
 525
 526         /* Logging change of state. */
 527         if (IS_DEBUG_OSPF(ism, ISM_STATUS))
 528                 zlog_debug("ISM[%s]: State change %s -> %s", IF_NAME(oi),
 529                            lookup_msg(ospf_ism_state_msg, oi->state, NULL),
 530                            lookup_msg(ospf_ism_state_msg, state, NULL));
 531
 532         old_state = oi->state;
 533         oi->state = state;
 534         oi->state_change++;
 535
 536         hook_call(ospf_ism_change, oi, state, old_state);
 537
 538         /* Set multicast memberships appropriately for new state. */
 539         ospf_if_set_multicast(oi);
 540
 541         if (old_state == ISM_Down || state == ISM_Down)
 542                 ospf_check_abr_status(oi->ospf);
 543
 544         /* Originate router-LSA. */
 545         if (state == ISM_Down) {
 546                 if (oi->area->act_ints > 0)
 547                         oi->area->act_ints--;
 548         } else if (old_state == ISM_Down)
 549                 oi->area->act_ints++;
 550
 551         /* schedule router-LSA originate. */
 552         ospf_router_lsa_update_area(oi->area);
 553
 554         /* Originate network-LSA. */
 555         if (old_state != ISM_DR && state == ISM_DR)
 556                 ospf_network_lsa_update(oi);
 557         else if (old_state == ISM_DR && state != ISM_DR) {
 558                 /* Free self originated network LSA. */
 559                 lsa = oi->network_lsa_self;
 560                 if (lsa)
 561                         ospf_lsa_flush_area(lsa, oi->area);
 562
 563                 ospf_lsa_unlock(&oi->network_lsa_self);
 564                 oi->network_lsa_self = NULL;
 565         }
 566
 567         ospf_opaque_ism_change(oi, old_state);
 568
 569         /* Check area border status.  */
 570         ospf_check_abr_status(oi->ospf);
 571 }
 572
 573 /* Execute ISM event process. */
 574 void ospf_ism_event(struct thread *thread)
 575 {
 576         int event;
 577         int next_state;
 578         struct ospf_interface *oi;
 579
 580         oi = THREAD_ARG(thread);
 581         event = THREAD_VAL(thread);
 582
 583         /* Call function. */
 584         next_state = (*(ISM[oi->state][event].func))(oi);
 585
 586         if (!next_state)
 587                 next_state = ISM[oi->state][event].next_state;
 588
 589         if (IS_DEBUG_OSPF(ism, ISM_EVENTS))
 590                 zlog_debug("ISM[%s]: %s (%s)", IF_NAME(oi),
 591                            lookup_msg(ospf_ism_state_msg, oi->state, NULL),
 592                            ospf_ism_event_str[event]);
 593
 594         /* If state is changed. */
 595         if (next_state != oi->state)
 596                 ism_change_state(oi, next_state);
 597
 598         /* Make sure timer is set. */
 599         ism_timer_set(oi);
 600 }