summaryrefslogtreecommitdiff
path: root/ospfd/ospf_spf.c
blob: bd9564d9e2cb07fa25b2abbe0d8777ddd0cd7975 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
/* OSPF SPF calculation.
   Copyright (C) 1999, 2000 Kunihiro Ishiguro, Toshiaki Takada

This file is part of GNU Zebra.

GNU Zebra is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.

GNU Zebra is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Zebra; see the file COPYING.  If not, write to the Free
Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.  */

#include <zebra.h>

#include "thread.h"
#include "memory.h"
#include "hash.h"
#include "linklist.h"
#include "prefix.h"
#include "if.h"
#include "table.h"
#include "log.h"
#include "sockunion.h"          /* for inet_ntop () */
#include "pqueue.h"

#include "ospfd/ospfd.h"
#include "ospfd/ospf_interface.h"
#include "ospfd/ospf_ism.h"
#include "ospfd/ospf_asbr.h"
#include "ospfd/ospf_lsa.h"
#include "ospfd/ospf_lsdb.h"
#include "ospfd/ospf_neighbor.h"
#include "ospfd/ospf_nsm.h"
#include "ospfd/ospf_spf.h"
#include "ospfd/ospf_route.h"
#include "ospfd/ospf_ia.h"
#include "ospfd/ospf_ase.h"
#include "ospfd/ospf_abr.h"
#include "ospfd/ospf_dump.h"

static void ospf_vertex_free (void *);
/* List of allocated vertices, to simplify cleanup of SPF.
 * Not thread-safe obviously. If it ever needs to be, it'd have to be
 * dynamically allocated at begin of ospf_spf_calculate
 */
static struct list vertex_list = { .del = ospf_vertex_free };

/* Heap related functions, for the managment of the candidates, to
 * be used with pqueue. */
static int
cmp (void * node1 , void * node2)
{
  struct vertex * v1 = (struct vertex *) node1;
  struct vertex * v2 = (struct vertex *) node2;
  if (v1 != NULL && v2 != NULL )
    {
      /* network vertices must be chosen before router vertices of same
       * cost in order to find all shortest paths
       */
      if ( ((v1->distance - v2->distance) == 0)
          && (v1->type != v2->type))
        {
          switch (v1->type)
            {
              case OSPF_VERTEX_NETWORK:
                return -1;
              case OSPF_VERTEX_ROUTER:
                return 1;
            }
        }
      else
        return (v1->distance - v2->distance);
    }
  return 0;
}

static void
update_stat (void *node , int position)
{
  struct vertex *v = node;

  /* Set the status of the vertex, when its position changes. */
  *(v->stat) = position;
}

static struct vertex_nexthop *
vertex_nexthop_new (void)
{
  return XCALLOC (MTYPE_OSPF_NEXTHOP, sizeof (struct vertex_nexthop));
}

static void
vertex_nexthop_free (struct vertex_nexthop *nh)
{
  XFREE (MTYPE_OSPF_NEXTHOP, nh);
}

/* Free the canonical nexthop objects for an area, ie the nexthop objects
 * attached to the first-hop router vertices, and any intervening network
 * vertices.
 */
static void
ospf_canonical_nexthops_free (struct vertex *root)
{
  struct listnode *node, *nnode;
  struct vertex *child;
  
  for (ALL_LIST_ELEMENTS (root->children, node, nnode, child))
    {
      struct listnode *n2, *nn2;
      struct vertex_parent *vp;
      
      /* router vertices through an attached network each
       * have a distinct (canonical / not inherited) nexthop
       * which must be freed.
       *
       * A network vertex can only have router vertices as its
       * children, so only one level of recursion is possible.
       */
      if (child->type == OSPF_VERTEX_NETWORK)
        ospf_canonical_nexthops_free (child);
      
      /* Free child nexthops pointing back to this root vertex */
      for (ALL_LIST_ELEMENTS (child->parents, n2, nn2, vp))
        if (vp->parent == root && vp->nexthop)
          vertex_nexthop_free (vp->nexthop);
    }
}      

/* TODO: Parent list should be excised, in favour of maintaining only
 * vertex_nexthop, with refcounts.
 */
static struct vertex_parent *
vertex_parent_new (struct vertex *v, int backlink, struct vertex_nexthop *hop)
{
  struct vertex_parent *new;
  
  new = XMALLOC (MTYPE_OSPF_VERTEX_PARENT, sizeof (struct vertex_parent));
  
  if (new == NULL)
    return NULL;
  
  new->parent = v;
  new->backlink = backlink;
  new->nexthop = hop;
  return new;
}

static void
vertex_parent_free (void *p)
{
  XFREE (MTYPE_OSPF_VERTEX_PARENT, p);
}

static struct vertex *
ospf_vertex_new (struct ospf_lsa *lsa)
{
  struct vertex *new;

  new = XCALLOC (MTYPE_OSPF_VERTEX, sizeof (struct vertex));

  new->flags = 0;
  new->stat = &(lsa->stat);
  new->type = lsa->data->type;
  new->id = lsa->data->id;
  new->lsa = lsa->data;
  new->children = list_new ();
  new->parents = list_new ();
  new->parents->del = vertex_parent_free;
  
  listnode_add (&vertex_list, new);
  
  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("%s: Created %s vertex %s", __func__,
                new->type == OSPF_VERTEX_ROUTER ? "Router" : "Network",
                inet_ntoa (new->lsa->id));
  return new;
}

static void
ospf_vertex_free (void *data)
{
  struct vertex *v = data;
  
  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("%s: Free %s vertex %s", __func__,
                v->type == OSPF_VERTEX_ROUTER ? "Router" : "Network",
                inet_ntoa (v->lsa->id));
  
  /* There should be no parents potentially holding references to this vertex
   * Children however may still be there, but presumably referenced by other
   * vertices
   */
  //assert (listcount (v->parents) == 0);
  
  if (v->children)
    list_delete (v->children);
  v->children = NULL;
  
  if (v->parents)
    list_delete (v->parents);
  v->parents = NULL;
  
  v->lsa = NULL;
  
  XFREE (MTYPE_OSPF_VERTEX, v);
}

static void
ospf_vertex_dump(const char *msg, struct vertex *v,
		 int print_parents, int print_children)
{
  if ( ! IS_DEBUG_OSPF_EVENT)
    return;

  zlog_debug("%s %s vertex %s  distance %u flags %u",
            msg,
	    v->type == OSPF_VERTEX_ROUTER ? "Router" : "Network",
	    inet_ntoa(v->lsa->id),
	    v->distance,
	    (unsigned int)v->flags);

  if (print_parents)
    {
      struct listnode *node;
      struct vertex_parent *vp;
      
      for (ALL_LIST_ELEMENTS_RO (v->parents, node, vp))
        {
	  char buf1[BUFSIZ];
	  
	  if (vp)
	    {
	      zlog_debug ("parent %s backlink %d nexthop %s  interface %s",
	                 inet_ntoa(vp->parent->lsa->id), vp->backlink,
			 inet_ntop(AF_INET, &vp->nexthop->router, buf1, BUFSIZ),
			 vp->nexthop->oi ? IF_NAME(vp->nexthop->oi) : "NULL");
	    }
	}
    }

  if (print_children)
    {
      struct listnode *cnode;
      struct vertex *cv;
      
      for (ALL_LIST_ELEMENTS_RO (v->children, cnode, cv))
        ospf_vertex_dump(" child:", cv, 0, 0);
    }
}


/* Add a vertex to the list of children in each of its parents. */
static void
ospf_vertex_add_parent (struct vertex *v)
{
  struct vertex_parent *vp;
  struct listnode *node;
  
  assert (v && v->parents);
  
  for (ALL_LIST_ELEMENTS_RO (v->parents, node, vp))
    {
      assert (vp->parent && vp->parent->children);
      
      /* No need to add two links from the same parent. */
      if (listnode_lookup (vp->parent->children, v) == NULL)
        listnode_add (vp->parent->children, v);
    }
}

static void
ospf_spf_init (struct ospf_area *area)
{
  struct vertex *v;
  
  /* Create root node. */
  v = ospf_vertex_new (area->router_lsa_self);
  
  area->spf = v;

  /* Reset ABR and ASBR router counts. */
  area->abr_count = 0;
  area->asbr_count = 0;
}

/* return index of link back to V from W, or -1 if no link found */
static int
ospf_lsa_has_link (struct lsa_header *w, struct lsa_header *v)
{
  unsigned int i, length;
  struct router_lsa *rl;
  struct network_lsa *nl;

  /* In case of W is Network LSA. */
  if (w->type == OSPF_NETWORK_LSA)
    {
      if (v->type == OSPF_NETWORK_LSA)
        return -1;

      nl = (struct network_lsa *) w;
      length = (ntohs (w->length) - OSPF_LSA_HEADER_SIZE - 4) / 4;

      for (i = 0; i < length; i++)
        if (IPV4_ADDR_SAME (&nl->routers[i], &v->id))
          return i;
      return -1;
    }

  /* In case of W is Router LSA. */
  if (w->type == OSPF_ROUTER_LSA)
    {
      rl = (struct router_lsa *) w;

      length = ntohs (w->length);

      for (i = 0;
           i < ntohs (rl->links) && length >= sizeof (struct router_lsa);
           i++, length -= 12)
        {
          switch (rl->link[i].type)
            {
            case LSA_LINK_TYPE_POINTOPOINT:
            case LSA_LINK_TYPE_VIRTUALLINK:
              /* Router LSA ID. */
              if (v->type == OSPF_ROUTER_LSA &&
                  IPV4_ADDR_SAME (&rl->link[i].link_id, &v->id))
                {
                  return i;
                }
              break;
            case LSA_LINK_TYPE_TRANSIT:
              /* Network LSA ID. */
              if (v->type == OSPF_NETWORK_LSA &&
                  IPV4_ADDR_SAME (&rl->link[i].link_id, &v->id))
                {
                  return i;
                }
              break;
            case LSA_LINK_TYPE_STUB:
              /* Stub can't lead anywhere, carry on */
              continue;
            default:
              break;
            }
        }
    }
  return -1;
}

/* Find the next link after prev_link from v to w.  If prev_link is
 * NULL, return the first link from v to w.  Ignore stub and virtual links;
 * these link types will never be returned.
 */
static struct router_lsa_link *
ospf_get_next_link (struct vertex *v, struct vertex *w,
                    struct router_lsa_link *prev_link)
{
  u_char *p;
  u_char *lim;
  u_char lsa_type =  LSA_LINK_TYPE_TRANSIT;
  struct router_lsa_link *l;

  if (w->type == OSPF_VERTEX_ROUTER)
    lsa_type = LSA_LINK_TYPE_POINTOPOINT;

  if (prev_link == NULL)
    p = ((u_char *) v->lsa) + OSPF_LSA_HEADER_SIZE + 4;
  else
    {
      p = (u_char *) prev_link;
      p += (OSPF_ROUTER_LSA_LINK_SIZE +
            (prev_link->m[0].tos_count * OSPF_ROUTER_LSA_TOS_SIZE));
    }

  lim = ((u_char *) v->lsa) + ntohs (v->lsa->length);

  while (p < lim)
    {
      l = (struct router_lsa_link *) p;

      p += (OSPF_ROUTER_LSA_LINK_SIZE + (l->m[0].tos_count * OSPF_ROUTER_LSA_TOS_SIZE));

      if (l->m[0].type != lsa_type)
        continue;

      if (IPV4_ADDR_SAME (&l->link_id, &w->id))
        return l;
    }

  return NULL;
}

static void
ospf_spf_flush_parents (struct vertex *w)
{
  struct vertex_parent *vp;
  struct listnode *ln, *nn;
  
  /* delete the existing nexthops */
  for (ALL_LIST_ELEMENTS (w->parents, ln, nn, vp))
    {
      list_delete_node (w->parents, ln);
      vertex_parent_free (vp);
    }
}

/* 
 * Consider supplied next-hop for inclusion to the supplied list of
 * equal-cost next-hops, adjust list as neccessary.  
 */
static void
ospf_spf_add_parent (struct vertex *v, struct vertex *w,
                     struct vertex_nexthop *newhop,
                     unsigned int distance)
{
  struct vertex_parent *vp, *wp;
  struct listnode *node;
    
  /* we must have a newhop, and a distance */
  assert (v && w && newhop);
  assert (distance);
  
  /* IFF w has already been assigned a distance, then we shouldn't get here
   * unless callers have determined V(l)->W is shortest / equal-shortest
   * path (0 is a special case distance (no distance yet assigned)).
   */
  if (w->distance)
    assert (distance <= w->distance);
  else
    w->distance = distance;
  
  if (IS_DEBUG_OSPF_EVENT)
    {
      char buf[2][INET_ADDRSTRLEN];
      zlog_debug ("%s: Adding %s as parent of %s",
                __func__,
                inet_ntop(AF_INET, &v->lsa->id, buf[0], sizeof(buf[0])),
                inet_ntop(AF_INET, &w->lsa->id, buf[1], sizeof(buf[1])));
    }           

  /* Adding parent for a new, better path: flush existing parents from W. */
  if (distance < w->distance)
    {
      if (IS_DEBUG_OSPF_EVENT)
        zlog_debug ("%s: distance %d better than %d, flushing existing parents",
                    __func__, distance, w->distance);
      ospf_spf_flush_parents (w);
      w->distance = distance;
    }
  
  /* new parent is <= existing parents, add it to parent list (if nexthop
   * not on parent list)
   */  
  for (ALL_LIST_ELEMENTS_RO(w->parents, node, wp))
    {
      if (memcmp(newhop, wp->nexthop, sizeof(*newhop)) == 0)
        {
          if (IS_DEBUG_OSPF_EVENT)
            zlog_debug ("%s: ... nexthop already on parent list, skipping add", __func__);
          return;
        }
    }

  vp = vertex_parent_new (v, ospf_lsa_has_link (w->lsa, v->lsa), newhop);
  listnode_add (w->parents, vp);

  return;
}

/* 16.1.1.  Calculate nexthop from root through V (parent) to
 * vertex W (destination), with given distance from root->W.
 *
 * The link must be supplied if V is the root vertex. In all other cases
 * it may be NULL.
 *
 * Note that this function may fail, hence the state of the destination
 * vertex, W, should /not/ be modified in a dependent manner until
 * this function returns. This function will update the W vertex with the
 * provided distance as appropriate.
 */
static unsigned int
ospf_nexthop_calculation (struct ospf_area *area, struct vertex *v,
                          struct vertex *w, struct router_lsa_link *l,
                          unsigned int distance, int lsa_pos)
{
  struct listnode *node, *nnode;
  struct vertex_nexthop *nh;
  struct vertex_parent *vp;
  struct ospf_interface *oi = NULL;
  unsigned int added = 0;
  char buf1[BUFSIZ];
  char buf2[BUFSIZ];

  if (IS_DEBUG_OSPF_EVENT)
    {
      zlog_debug ("ospf_nexthop_calculation(): Start");
      ospf_vertex_dump("V (parent):", v, 1, 1);
      ospf_vertex_dump("W (dest)  :", w, 1, 1);
      zlog_debug ("V->W distance: %d", distance);
    }

  if (v == area->spf)
    {      
      /* 16.1.1 para 4.  In the first case, the parent vertex (V) is the
	 root (the calculating router itself).  This means that the 
	 destination is either a directly connected network or directly
	 connected router.  The outgoing interface in this case is simply 
         the OSPF interface connecting to the destination network/router.
      */

      /* we *must* be supplied with the link data */
      assert (l != NULL);
      oi = ospf_if_lookup_by_lsa_pos (area, lsa_pos);
      if (!oi)
	{
	  zlog_debug("%s: OI not found in LSA: lsa_pos:%d link_id:%s link_data:%s",
		     __func__, lsa_pos,
		     inet_ntop (AF_INET, &l->link_id, buf1, BUFSIZ),
		     inet_ntop (AF_INET, &l->link_data, buf2, BUFSIZ));
	  return 0;
	}

      if (IS_DEBUG_OSPF_EVENT)
	{
	  zlog_debug("%s: considering link:%s "
		     "type:%d link_id:%s link_data:%s",
		     __func__, oi->ifp->name, l->m[0].type,
		     inet_ntop (AF_INET, &l->link_id, buf1, BUFSIZ),
		     inet_ntop (AF_INET, &l->link_data, buf2, BUFSIZ));
	}

      if (w->type == OSPF_VERTEX_ROUTER)
        {
          /* l  is a link from v to w
           * l2 will be link from w to v
           */
          struct router_lsa_link *l2 = NULL;

          if (l->m[0].type == LSA_LINK_TYPE_POINTOPOINT)
            {
	      struct in_addr nexthop;

              /* If the destination is a router which connects to
                 the calculating router via a Point-to-MultiPoint
                 network, the destination's next hop IP address(es)
                 can be determined by examining the destination's
                 router-LSA: each link pointing back to the
                 calculating router and having a Link Data field
                 belonging to the Point-to-MultiPoint network
                 provides an IP address of the next hop router.

                 At this point l is a link from V to W, and V is the
                 root ("us"). If it is a point-to-multipoint interface,
		 then look through the links in the opposite direction (W to V).
		 If any of them have an address that lands within the
                 subnet declared by the PtMP link, then that link
                 is a constituent of the PtMP link, and its address is
                 a nexthop address for V.
              */
	      if (oi->type == OSPF_IFTYPE_POINTOPOINT)
		{
		  /* Having nexthop = 0 is tempting, but NOT acceptable.
		     It breaks AS-External routes with a forwarding address,
		     since ospf_ase_complete_direct_routes() will mistakenly
		     assume we've reached the last hop and should place the
		     forwarding address as nexthop.
		     Also, users may configure multi-access links in p2p mode,
		     so we need the IP to ARP the nexthop.
		  */
		  struct ospf_neighbor *nbr_w;

		  nbr_w = ospf_nbr_lookup_by_routerid (oi->nbrs, &l->link_id);
		  if (nbr_w != NULL)
		    {
		      added = 1;
		      nexthop = nbr_w->src;
		    }
		}
	      else if (oi->type == OSPF_IFTYPE_POINTOMULTIPOINT)
		{
		  struct prefix_ipv4 la;

		  la.family = AF_INET;
		  la.prefixlen = oi->address->prefixlen;

		  /* V links to W on PtMP interface
		     - find the interface address on W */
		  while ((l2 = ospf_get_next_link (w, v, l2)))
		    {
		      la.prefix = l2->link_data;

		      if (prefix_cmp ((struct prefix *) &la,
				      oi->address) != 0)
			continue;
		      /* link_data is on our PtMP network */
		      added = 1;
		      nexthop = l2->link_data;
		      break;
		    }
		}

              if (added)
                {
                  /* found all necessary info to build nexthop */
                  nh = vertex_nexthop_new ();
                  nh->oi = oi;
                  nh->router = nexthop;
                  ospf_spf_add_parent (v, w, nh, distance);
                  return 1;
                }
              else
		zlog_info("%s: could not determine nexthop for link %s",
			  __func__, oi->ifp->name);
            } /* end point-to-point link from V to W */
          else if (l->m[0].type == LSA_LINK_TYPE_VIRTUALLINK)
            {
              struct ospf_vl_data *vl_data;
              
              /* VLink implementation limitations: 
               * a) vl_data can only reference one nexthop, so no ECMP
               *    to backbone through VLinks. Though transit-area 
               *    summaries may be considered, and those can be ECMP.
               * b) We can only use /one/ VLink, even if multiple ones
               *    exist this router through multiple transit-areas.
               */
              vl_data = ospf_vl_lookup (area->ospf, NULL, l->link_id);
              
              if (vl_data 
                  && CHECK_FLAG (vl_data->flags, OSPF_VL_FLAG_APPROVED))
                {
                  nh = vertex_nexthop_new ();
                  nh->oi = vl_data->nexthop.oi;
                  nh->router = vl_data->nexthop.router;
                  ospf_spf_add_parent (v, w, nh, distance);
                  return 1;
                }
              else
                  zlog_info("ospf_nexthop_calculation(): "
                            "vl_data for VL link not found");
            } /* end virtual-link from V to W */
          return 0;
        } /* end W is a Router vertex */
      else
        {
          assert(w->type == OSPF_VERTEX_NETWORK);

	  nh = vertex_nexthop_new ();
	  nh->oi = oi;
	  nh->router.s_addr = 0; /* Nexthop not required */
	  ospf_spf_add_parent (v, w, nh, distance);
	  return 1;
        }
    } /* end V is the root */
  /* Check if W's parent is a network connected to root. */
  else if (v->type == OSPF_VERTEX_NETWORK)
    {
      /* See if any of V's parents are the root. */
      for (ALL_LIST_ELEMENTS (v->parents, node, nnode, vp))
        {
          if (vp->parent == area->spf) /* connects to root? */
	    {
	      /* 16.1.1 para 5. ...the parent vertex is a network that
	       * directly connects the calculating router to the destination
	       * router.  The list of next hops is then determined by
	       * examining the destination's router-LSA...
	       */

	      assert(w->type == OSPF_VERTEX_ROUTER);
              while ((l = ospf_get_next_link (w, v, l)))
                {
		  /* ...For each link in the router-LSA that points back to the
		   * parent network, the link's Link Data field provides the IP
		   * address of a next hop router.  The outgoing interface to
		   * use can then be derived from the next hop IP address (or 
		   * it can be inherited from the parent network).
		   */
		  nh = vertex_nexthop_new ();
		  nh->oi = vp->nexthop->oi;
		  nh->router = l->link_data;
		  added = 1;
                  ospf_spf_add_parent (v, w, nh, distance);
                }
              /* Note lack of return is deliberate. See next comment. */
          }
        }
      /* NB: This code is non-trivial.
       * 
       * E.g. it is not enough to know that V connects to the root. It is
       * also important that the while above, looping through all links from
       * W->V found at least one link, so that we know there is
       * bi-directional connectivity between V and W (which need not be the
       * case, e.g.  when OSPF has not yet converged fully).  Otherwise, if
       * we /always/ return here, without having checked that root->V->-W
       * actually resulted in a valid nexthop being created, then we we will
       * prevent SPF from finding/using higher cost paths.
       *
       * It is important, if root->V->W has not been added, that we continue
       * through to the intervening-router nexthop code below.  So as to
       * ensure other paths to V may be used.  This avoids unnecessary
       * blackholes while OSPF is convergening.
       *
       * I.e. we may have arrived at this function, examining V -> W, via
       * workable paths other than root -> V, and it's important to avoid
       * getting "confused" by non-working root->V->W path - it's important
       * to *not* lose the working non-root paths, just because of a
       * non-viable root->V->W.
       *
       * See also bug #330 (required reading!), and:
       *
       * http://blogs.oracle.com/paulj/entry/the_difference_a_line_makes
       */
      if (added)
        return added;
    }

  /* 16.1.1 para 4.  If there is at least one intervening router in the
   * current shortest path between the destination and the root, the
   * destination simply inherits the set of next hops from the
   * parent.
   */
  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("%s: Intervening routers, adding parent(s)", __func__);

  for (ALL_LIST_ELEMENTS (v->parents, node, nnode, vp))
    {
      added = 1;
      ospf_spf_add_parent (v, w, vp->nexthop, distance);
    }
  
  return added;
}

/* RFC2328 Section 16.1 (2).
 * v is on the SPF tree.  Examine the links in v's LSA.  Update the list
 * of candidates with any vertices not already on the list.  If a lower-cost
 * path is found to a vertex already on the candidate list, store the new cost.
 */
static void
ospf_spf_next (struct vertex *v, struct ospf_area *area,
	       struct pqueue * candidate)
{
  struct ospf_lsa *w_lsa = NULL;
  u_char *p;
  u_char *lim;
  struct router_lsa_link *l = NULL;
  struct in_addr *r;
  int type = 0, lsa_pos=-1, lsa_pos_next=0;

  /* If this is a router-LSA, and bit V of the router-LSA (see Section
     A.4.2:RFC2328) is set, set Area A's TransitCapability to TRUE.  */
  if (v->type == OSPF_VERTEX_ROUTER)
    {
      if (IS_ROUTER_LSA_VIRTUAL ((struct router_lsa *) v->lsa))
        area->transit = OSPF_TRANSIT_TRUE;
    }
  
  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("%s: Next vertex of %s vertex %s",
                __func__, 
                v->type == OSPF_VERTEX_ROUTER ? "Router" : "Network",
                inet_ntoa(v->lsa->id));
  
  p = ((u_char *) v->lsa) + OSPF_LSA_HEADER_SIZE + 4;
  lim = ((u_char *) v->lsa) + ntohs (v->lsa->length);

  while (p < lim)
    {
      struct vertex *w;
      unsigned int distance;
      
      /* In case of V is Router-LSA. */
      if (v->lsa->type == OSPF_ROUTER_LSA)
        {
          l = (struct router_lsa_link *) p;

	  lsa_pos = lsa_pos_next; /* LSA link position */
	  lsa_pos_next++;
          p += (OSPF_ROUTER_LSA_LINK_SIZE +
                (l->m[0].tos_count * OSPF_ROUTER_LSA_TOS_SIZE));

          /* (a) If this is a link to a stub network, examine the next
             link in V's LSA.  Links to stub networks will be
             considered in the second stage of the shortest path
             calculation. */
          if ((type = l->m[0].type) == LSA_LINK_TYPE_STUB)
            continue;
          
          /* Infinite distance links shouldn't be followed, except
           * for local links (a stub-routed router still wants to
           * calculate tree, so must follow its own links).
           */
          if ((v != area->spf) && l->m[0].metric >= OSPF_OUTPUT_COST_INFINITE)
            continue;

          /* (b) Otherwise, W is a transit vertex (router or transit
             network).  Look up the vertex W's LSA (router-LSA or
             network-LSA) in Area A's link state database. */
          switch (type)
            {
            case LSA_LINK_TYPE_POINTOPOINT:
            case LSA_LINK_TYPE_VIRTUALLINK:
              if (type == LSA_LINK_TYPE_VIRTUALLINK)
                {
                  if (IS_DEBUG_OSPF_EVENT)
                    zlog_debug ("looking up LSA through VL: %s",
                               inet_ntoa (l->link_id));
                }

              w_lsa = ospf_lsa_lookup (area, OSPF_ROUTER_LSA, l->link_id,
                                       l->link_id);
              if (w_lsa)
                {
                  if (IS_DEBUG_OSPF_EVENT)
                    zlog_debug ("found Router LSA %s", inet_ntoa (l->link_id));
                }
              break;
            case LSA_LINK_TYPE_TRANSIT:
              if (IS_DEBUG_OSPF_EVENT)
                zlog_debug ("Looking up Network LSA, ID: %s",
                           inet_ntoa (l->link_id));
              w_lsa = ospf_lsa_lookup_by_id (area, OSPF_NETWORK_LSA,
                                             l->link_id);
              if (w_lsa)
                if (IS_DEBUG_OSPF_EVENT)
                  zlog_debug ("found the LSA");
              break;
            default:
              zlog_warn ("Invalid LSA link type %d", type);
              continue;
            }
        }
      else
        {
          /* In case of V is Network-LSA. */
          r = (struct in_addr *) p;
          p += sizeof (struct in_addr);

          /* Lookup the vertex W's LSA. */
          w_lsa = ospf_lsa_lookup_by_id (area, OSPF_ROUTER_LSA, *r);
          if (w_lsa)
            {
              if (IS_DEBUG_OSPF_EVENT)
                zlog_debug ("found Router LSA %s", inet_ntoa (w_lsa->data->id));
            }
        }

      /* (b cont.) If the LSA does not exist, or its LS age is equal
         to MaxAge, or it does not have a link back to vertex V,
         examine the next link in V's LSA.[23] */
      if (w_lsa == NULL)
        {
          if (IS_DEBUG_OSPF_EVENT)
            zlog_debug ("No LSA found");
          continue;
        }

      if (IS_LSA_MAXAGE (w_lsa))
        {
          if (IS_DEBUG_OSPF_EVENT)
            zlog_debug ("LSA is MaxAge");
          continue;
        }

      if (ospf_lsa_has_link (w_lsa->data, v->lsa) < 0 )
        {
          if (IS_DEBUG_OSPF_EVENT)
            zlog_debug ("The LSA doesn't have a link back");
          continue;
        }

      /* (c) If vertex W is already on the shortest-path tree, examine
         the next link in the LSA. */
      if (w_lsa->stat == LSA_SPF_IN_SPFTREE)
	{
	  if (IS_DEBUG_OSPF_EVENT)
	    zlog_debug ("The LSA is already in SPF");
	  continue;
	}

      /* (d) Calculate the link state cost D of the resulting path
         from the root to vertex W.  D is equal to the sum of the link
         state cost of the (already calculated) shortest path to
         vertex V and the advertised cost of the link between vertices
         V and W.  If D is: */

      /* calculate link cost D. */
      if (v->lsa->type == OSPF_ROUTER_LSA)
	distance = v->distance + ntohs (l->m[0].metric);
      else /* v is not a Router-LSA */
	distance = v->distance;

      /* Is there already vertex W in candidate list? */
      if (w_lsa->stat == LSA_SPF_NOT_EXPLORED)
	{
          /* prepare vertex W. */
          w = ospf_vertex_new (w_lsa);

          /* Calculate nexthop to W. */
          if (ospf_nexthop_calculation (area, v, w, l, distance, lsa_pos))
            pqueue_enqueue (w, candidate);
          else if (IS_DEBUG_OSPF_EVENT)
            zlog_debug ("Nexthop Calc failed");
	}
      else if (w_lsa->stat >= 0)
	{
	  /* Get the vertex from candidates. */
	  w = candidate->array[w_lsa->stat];

	  /* if D is greater than. */  
	  if (w->distance < distance)
            {
              continue;
            }
          /* equal to. */
	  else if (w->distance == distance)
            {
	      /* Found an equal-cost path to W.  
               * Calculate nexthop of to W from V. */
	      ospf_nexthop_calculation (area, v, w, l, distance, lsa_pos);
            }
           /* less than. */
	  else
            {
              /* Found a lower-cost path to W.
               * nexthop_calculation is conditional, if it finds
               * valid nexthop it will call spf_add_parents, which
               * will flush the old parents
               */
	      if (ospf_nexthop_calculation (area, v, w, l, distance, lsa_pos))
                /* Decrease the key of the node in the heap.
                 * trickle-sort it up towards root, just in case this
                 * node should now be the new root due the cost change. 
                 * (next pqueu_{de,en}queue will fully re-heap the queue).
                 */
                trickle_up (w_lsa->stat, candidate);
            }
        } /* end W is already on the candidate list */
    } /* end loop over the links in V's LSA */
}

static void
ospf_spf_dump (struct vertex *v, int i)
{
  struct listnode *cnode;
  struct listnode *nnode;
  struct vertex_parent *parent;

  if (v->type == OSPF_VERTEX_ROUTER)
    {
      if (IS_DEBUG_OSPF_EVENT)
        zlog_debug ("SPF Result: %d [R] %s", i, inet_ntoa (v->lsa->id));
    }
  else
    {
      struct network_lsa *lsa = (struct network_lsa *) v->lsa;
      if (IS_DEBUG_OSPF_EVENT)
        zlog_debug ("SPF Result: %d [N] %s/%d", i, inet_ntoa (v->lsa->id),
                   ip_masklen (lsa->mask));
    }

  if (IS_DEBUG_OSPF_EVENT)
    for (ALL_LIST_ELEMENTS_RO (v->parents, nnode, parent))
      {
        zlog_debug (" nexthop %p %s %s", 
                    parent->nexthop,
                    inet_ntoa (parent->nexthop->router),
                    parent->nexthop->oi ? IF_NAME(parent->nexthop->oi)
                                        : "NULL");
      }

  i++;

  for (ALL_LIST_ELEMENTS_RO (v->children, cnode, v))
    ospf_spf_dump (v, i);
}

/* Second stage of SPF calculation. */
static void
ospf_spf_process_stubs (struct ospf_area *area, struct vertex *v,
                        struct route_table *rt,
                        int parent_is_root)
{
  struct listnode *cnode, *cnnode;
  struct vertex *child;

  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("ospf_process_stub():processing stubs for area %s",
               inet_ntoa (area->area_id));
  if (v->type == OSPF_VERTEX_ROUTER)
    {
      u_char *p;
      u_char *lim;
      struct router_lsa_link *l;
      struct router_lsa *rlsa;
      int lsa_pos = 0;

      if (IS_DEBUG_OSPF_EVENT)
        zlog_debug ("ospf_process_stubs():processing router LSA, id: %s",
                   inet_ntoa (v->lsa->id));
      rlsa = (struct router_lsa *) v->lsa;


      if (IS_DEBUG_OSPF_EVENT)
        zlog_debug ("ospf_process_stubs(): we have %d links to process",
                   ntohs (rlsa->links));
      p = ((u_char *) v->lsa) + OSPF_LSA_HEADER_SIZE + 4;
      lim = ((u_char *) v->lsa) + ntohs (v->lsa->length);

      while (p < lim)
        {
          l = (struct router_lsa_link *) p;

          p += (OSPF_ROUTER_LSA_LINK_SIZE +
                (l->m[0].tos_count * OSPF_ROUTER_LSA_TOS_SIZE));

          if (l->m[0].type == LSA_LINK_TYPE_STUB)
	    ospf_intra_add_stub (rt, l, v, area, parent_is_root, lsa_pos);
	  lsa_pos++;
        }
    }

  ospf_vertex_dump("ospf_process_stubs(): after examining links: ", v, 1, 1);

  for (ALL_LIST_ELEMENTS (v->children, cnode, cnnode, child))
    {
      if (CHECK_FLAG (child->flags, OSPF_VERTEX_PROCESSED))
        continue;
      
      /* the first level of routers connected to the root
       * should have 'parent_is_root' set, including those 
       * connected via a network vertex.
       */
      if (area->spf == v)
        parent_is_root = 1;
      else if (v->type == OSPF_VERTEX_ROUTER)
        parent_is_root = 0;
        
      ospf_spf_process_stubs (area, child, rt, parent_is_root);

      SET_FLAG (child->flags, OSPF_VERTEX_PROCESSED);
    }
}

void
ospf_rtrs_free (struct route_table *rtrs)
{
  struct route_node *rn;
  struct list *or_list;
  struct ospf_route *or;
  struct listnode *node, *nnode;

  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("Route: Router Routing Table free");

  for (rn = route_top (rtrs); rn; rn = route_next (rn))
    if ((or_list = rn->info) != NULL)
      {
        for (ALL_LIST_ELEMENTS (or_list, node, nnode, or))
          ospf_route_free (or);

        list_delete (or_list);

        /* Unlock the node. */
        rn->info = NULL;
        route_unlock_node (rn);
      }
  route_table_finish (rtrs);
}

#if 0
static void
ospf_rtrs_print (struct route_table *rtrs)
{
  struct route_node *rn;
  struct list *or_list;
  struct listnode *ln;
  struct listnode *pnode;
  struct ospf_route *or;
  struct ospf_path *path;
  char buf1[BUFSIZ];
  char buf2[BUFSIZ];

  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("ospf_rtrs_print() start");

  for (rn = route_top (rtrs); rn; rn = route_next (rn))
    if ((or_list = rn->info) != NULL)
      for (ALL_LIST_ELEMENTS_RO (or_list, ln, or))
        {
          switch (or->path_type)
            {
            case OSPF_PATH_INTRA_AREA:
              if (IS_DEBUG_OSPF_EVENT)
                zlog_debug ("%s   [%d] area: %s",
                           inet_ntop (AF_INET, &or->id, buf1, BUFSIZ),
                           or->cost, inet_ntop (AF_INET, &or->u.std.area_id,
                                                buf2, BUFSIZ));
              break;
            case OSPF_PATH_INTER_AREA:
              if (IS_DEBUG_OSPF_EVENT)
                zlog_debug ("%s IA [%d] area: %s",
                           inet_ntop (AF_INET, &or->id, buf1, BUFSIZ),
                           or->cost, inet_ntop (AF_INET, &or->u.std.area_id,
                                                buf2, BUFSIZ));
              break;
            default:
              break;
            }

          for (ALL_LIST_ELEMENTS_RO (or->paths, pnode, path))
            {
              if (path->nexthop.s_addr == 0)
                {
                  if (IS_DEBUG_OSPF_EVENT)
                    zlog_debug ("   directly attached to %s\r\n",
				ifindex2ifname (path->ifindex));
                }
              else
                {
                  if (IS_DEBUG_OSPF_EVENT)
                    zlog_debug ("   via %s, %s\r\n",
				inet_ntoa (path->nexthop),
				ifindex2ifname (path->ifindex));
                }
            }
        }

  zlog_debug ("ospf_rtrs_print() end");
}
#endif

/* Calculating the shortest-path tree for an area. */
static void
ospf_spf_calculate (struct ospf_area *area, struct route_table *new_table,
                    struct route_table *new_rtrs)
{
  struct pqueue *candidate;
  struct vertex *v;
  
  if (IS_DEBUG_OSPF_EVENT)
    {
      zlog_debug ("ospf_spf_calculate: Start");
      zlog_debug ("ospf_spf_calculate: running Dijkstra for area %s",
                 inet_ntoa (area->area_id));
    }

  /* Check router-lsa-self.  If self-router-lsa is not yet allocated,
     return this area's calculation. */
  if (!area->router_lsa_self)
    {
      if (IS_DEBUG_OSPF_EVENT)
        zlog_debug ("ospf_spf_calculate: "
                   "Skip area %s's calculation due to empty router_lsa_self",
                   inet_ntoa (area->area_id));
      return;
    }

  /* RFC2328 16.1. (1). */
  /* Initialize the algorithm's data structures. */
  
  /* This function scans all the LSA database and set the stat field to
   * LSA_SPF_NOT_EXPLORED. */
  ospf_lsdb_clean_stat (area->lsdb);
  /* Create a new heap for the candidates. */ 
  candidate = pqueue_create();
  candidate->cmp = cmp;
  candidate->update = update_stat;

  /* Initialize the shortest-path tree to only the root (which is the
     router doing the calculation). */
  ospf_spf_init (area);
  v = area->spf;
  /* Set LSA position to LSA_SPF_IN_SPFTREE. This vertex is the root of the
   * spanning tree. */
  *(v->stat) = LSA_SPF_IN_SPFTREE;

  /* Set Area A's TransitCapability to FALSE. */
  area->transit = OSPF_TRANSIT_FALSE;
  area->shortcut_capability = 1;
  
  for (;;)
    {
      /* RFC2328 16.1. (2). */
      ospf_spf_next (v, area, candidate);

      /* RFC2328 16.1. (3). */
      /* If at this step the candidate list is empty, the shortest-
         path tree (of transit vertices) has been completely built and
         this stage of the procedure terminates. */
      if (candidate->size == 0)
        break;

      /* Otherwise, choose the vertex belonging to the candidate list
         that is closest to the root, and add it to the shortest-path
         tree (removing it from the candidate list in the
         process). */
      /* Extract from the candidates the node with the lower key. */
      v = (struct vertex *) pqueue_dequeue (candidate);
      /* Update stat field in vertex. */
      *(v->stat) = LSA_SPF_IN_SPFTREE;

      ospf_vertex_add_parent (v);

      /* RFC2328 16.1. (4). */
      if (v->type == OSPF_VERTEX_ROUTER)
        ospf_intra_add_router (new_rtrs, v, area);
      else
        ospf_intra_add_transit (new_table, v, area);

      /* RFC2328 16.1. (5). */
      /* Iterate the algorithm by returning to Step 2. */

    } /* end loop until no more candidate vertices */

  if (IS_DEBUG_OSPF_EVENT)
    {
      ospf_spf_dump (area->spf, 0);
      ospf_route_table_dump (new_table);
    }

  /* Second stage of SPF calculation procedure's  */
  ospf_spf_process_stubs (area, area->spf, new_table, 0);

  /* Free candidate queue. */
  pqueue_delete (candidate);
  
  ospf_vertex_dump (__func__, area->spf, 0, 1);
  /* Free nexthop information, canonical versions of which are attached
   * the first level of router vertices attached to the root vertex, see
   * ospf_nexthop_calculation.
   */
  ospf_canonical_nexthops_free (area->spf);
  
  /* Free SPF vertices, but not the list. List has ospf_vertex_free
   * as deconstructor.
   */
  list_delete_all_node (&vertex_list);
  
  /* Increment SPF Calculation Counter. */
  area->spf_calculation++;

  quagga_gettime (QUAGGA_CLK_MONOTONIC, &area->ospf->ts_spf);

  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("ospf_spf_calculate: Stop. %ld vertices",
                mtype_stats_alloc(MTYPE_OSPF_VERTEX));
}

/* Timer for SPF calculation. */
static int
ospf_spf_calculate_timer (struct thread *thread)
{
  struct ospf *ospf = THREAD_ARG (thread);
  struct route_table *new_table, *new_rtrs;
  struct ospf_area *area;
  struct listnode *node, *nnode;

  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("SPF: Timer (SPF calculation expire)");

  ospf->t_spf_calc = NULL;

  /* Allocate new table tree. */
  new_table = route_table_init ();
  new_rtrs = route_table_init ();

  ospf_vl_unapprove (ospf);

  /* Calculate SPF for each area. */
  for (ALL_LIST_ELEMENTS (ospf->areas, node, nnode, area))
    {
      /* Do backbone last, so as to first discover intra-area paths
       * for any back-bone virtual-links
       */
      if (ospf->backbone && ospf->backbone == area)
        continue;
      
      ospf_spf_calculate (area, new_table, new_rtrs);
    }
  
  /* SPF for backbone, if required */
  if (ospf->backbone)
    ospf_spf_calculate (ospf->backbone, new_table, new_rtrs);
  
  ospf_vl_shut_unapproved (ospf);

  ospf_ia_routing (ospf, new_table, new_rtrs);

  ospf_prune_unreachable_networks (new_table);
  ospf_prune_unreachable_routers (new_rtrs);

  /* AS-external-LSA calculation should not be performed here. */

  /* If new Router Route is installed,
     then schedule re-calculate External routes. */
  if (1)
    ospf_ase_calculate_schedule (ospf);

  ospf_ase_calculate_timer_add (ospf);

  /* Update routing table. */
  ospf_route_install (ospf, new_table);

  /* Update ABR/ASBR routing table */
  if (ospf->old_rtrs)
    {
      /* old_rtrs's node holds linked list of ospf_route. --kunihiro. */
      /* ospf_route_delete (ospf->old_rtrs); */
      ospf_rtrs_free (ospf->old_rtrs);
    }

  ospf->old_rtrs = ospf->new_rtrs;
  ospf->new_rtrs = new_rtrs;

  if (IS_OSPF_ABR (ospf))
    ospf_abr_task (ospf);

  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("SPF: calculation complete");

  return 0;
}

/* Add schedule for SPF calculation.  To avoid frequenst SPF calc, we
   set timer for SPF calc. */
void
ospf_spf_calculate_schedule (struct ospf *ospf)
{
  unsigned long delay, elapsed, ht;
  struct timeval result;

  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("SPF: calculation timer scheduled");

  /* OSPF instance does not exist. */
  if (ospf == NULL)
    return;
  
  /* SPF calculation timer is already scheduled. */
  if (ospf->t_spf_calc)
    {
      if (IS_DEBUG_OSPF_EVENT)
        zlog_debug ("SPF: calculation timer is already scheduled: %p",
                   ospf->t_spf_calc);
      return;
    }
  
  /* XXX Monotic timers: we only care about relative time here. */
  result = tv_sub (recent_relative_time (), ospf->ts_spf);
  
  elapsed = (result.tv_sec * 1000) + (result.tv_usec / 1000);
  ht = ospf->spf_holdtime * ospf->spf_hold_multiplier;
  
  if (ht > ospf->spf_max_holdtime)
    ht = ospf->spf_max_holdtime;
  
  /* Get SPF calculation delay time. */
  if (elapsed < ht)
    {
      /* Got an event within the hold time of last SPF. We need to
       * increase the hold_multiplier, if it's not already at/past
       * maximum value, and wasn't already increased..
       */
      if (ht < ospf->spf_max_holdtime)
        ospf->spf_hold_multiplier++;
      
      /* always honour the SPF initial delay */
      if ( (ht - elapsed) < ospf->spf_delay)
        delay = ospf->spf_delay;
      else
        delay = ht - elapsed;
    }
  else
    {
      /* Event is past required hold-time of last SPF */
      delay = ospf->spf_delay;
      ospf->spf_hold_multiplier = 1;
    }
  
  if (IS_DEBUG_OSPF_EVENT)
    zlog_debug ("SPF: calculation timer delay = %ld", delay);

  ospf->t_spf_calc =
    thread_add_timer_msec (master, ospf_spf_calculate_timer, ospf, delay);
}