[mirror_frr.git] / ospfd / ospf_ase.c

/*
 * OSPF AS external route calculation.
 * Copyright (C) 1999, 2000 Alex Zinin, 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 this program; see the file COPYING; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 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 "vty.h"
#include "log.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_ase.h"
#include "ospfd/ospf_zebra.h"
#include "ospfd/ospf_dump.h"

struct ospf_route *ospf_find_asbr_route(struct ospf *ospf,
                                        struct route_table *rtrs,
                                        struct prefix_ipv4 *asbr)
{
        struct route_node *rn;
        struct ospf_route * or, *best = NULL;
        struct listnode *node;
        struct list *chosen;

        /* Sanity check. */
        if (rtrs == NULL)
                return NULL;

        rn = route_node_lookup(rtrs, (struct prefix *)asbr);
        if (!rn)
                return NULL;

        route_unlock_node(rn);

        chosen = list_new();

        /* First try to find intra-area non-bb paths. */
        if (!CHECK_FLAG(ospf->config, OSPF_RFC1583_COMPATIBLE))
                for (ALL_LIST_ELEMENTS_RO((struct list *)rn->info, node, or))
                        if (or->cost < OSPF_LS_INFINITY)
                                if (!OSPF_IS_AREA_ID_BACKBONE(or->u.std.area_id)
                                            &&
                                    or->path_type == OSPF_PATH_INTRA_AREA)
                                        listnode_add(chosen, or);

        /* If none is found -- look through all. */
        if (listcount(chosen) == 0) {
                list_delete(&chosen);
                chosen = rn->info;
        }

        /* Now find the route with least cost. */
        for (ALL_LIST_ELEMENTS_RO(chosen, node, or))
                if (or->cost < OSPF_LS_INFINITY) {
                        if (best == NULL)
                                best = or ;
                        else if (best->cost > or->cost)
                                best = or ;
                        else if (best->cost ==
                                 or->cost
                                           && IPV4_ADDR_CMP(
                                                      &best->u.std.area_id,
                                                      & or->u.std.area_id)
                                                      < 0)
                                best = or ;
                }

        if (chosen != rn->info)
                list_delete(&chosen);

        return best;
}

struct ospf_route *ospf_find_asbr_route_through_area(struct route_table *rtrs,
                                                     struct prefix_ipv4 *asbr,
                                                     struct ospf_area *area)
{
        struct route_node *rn;

        /* Sanity check. */
        if (rtrs == NULL)
                return NULL;

        rn = route_node_lookup(rtrs, (struct prefix *)asbr);

        if (rn) {
                struct listnode *node;
                struct ospf_route * or ;

                route_unlock_node(rn);

                for (ALL_LIST_ELEMENTS_RO((struct list *)rn->info, node, or))
                        if (IPV4_ADDR_SAME(& or->u.std.area_id, &area->area_id))
                                return or ;
        }

        return NULL;
}

static void ospf_ase_complete_direct_routes(struct ospf_route *ro,
                                            struct in_addr nexthop)
{
        struct listnode *node;
        struct ospf_path *op;

        for (ALL_LIST_ELEMENTS_RO(ro->paths, node, op))
                if (op->nexthop.s_addr == INADDR_ANY)
                        op->nexthop.s_addr = nexthop.s_addr;
}

static int ospf_ase_forward_address_check(struct ospf *ospf,
                                          struct in_addr fwd_addr)
{
        struct listnode *ifn;
        struct ospf_interface *oi;

        for (ALL_LIST_ELEMENTS_RO(ospf->oiflist, ifn, oi))
                if (if_is_operative(oi->ifp))
                        if (oi->type != OSPF_IFTYPE_VIRTUALLINK)
                                if (IPV4_ADDR_SAME(&oi->address->u.prefix4,
                                                   &fwd_addr))
                                        return 0;

        return 1;
}

static struct ospf_route *
ospf_ase_calculate_new_route(struct ospf_lsa *lsa,
                             struct ospf_route *asbr_route, uint32_t metric)
{
        struct as_external_lsa *al;
        struct ospf_route *new;

        al = (struct as_external_lsa *)lsa->data;

        new = ospf_route_new();

        /* Set redistributed type -- does make sense? */
        /* new->type = type; */
        new->id = al->header.id;
        new->mask = al->mask;

        if (!IS_EXTERNAL_METRIC(al->e[0].tos)) {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug("Route[External]: type-1 created.");
                new->path_type = OSPF_PATH_TYPE1_EXTERNAL;
                new->cost = asbr_route->cost + metric; /* X + Y */
        } else {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug("Route[External]: type-2 created.");
                new->path_type = OSPF_PATH_TYPE2_EXTERNAL;
                new->cost = asbr_route->cost;   /* X */
                new->u.ext.type2_cost = metric; /* Y */
        }

        new->type = OSPF_DESTINATION_NETWORK;
        new->u.ext.origin = lsa;
        new->u.ext.tag = ntohl(al->e[0].route_tag);
        new->u.ext.asbr = asbr_route;

        assert(new != asbr_route);

        return new;
}

#define OSPF_ASE_CALC_INTERVAL 1

int ospf_ase_calculate_route(struct ospf *ospf, struct ospf_lsa *lsa)
{
        uint32_t metric;
        struct as_external_lsa *al;
        struct ospf_route *asbr_route;
        struct prefix_ipv4 asbr, p;
        struct route_node *rn;
        struct ospf_route *new, * or ;
        int ret;

        assert(lsa);
        al = (struct as_external_lsa *)lsa->data;

        if (lsa->data->type == OSPF_AS_NSSA_LSA)
                if (IS_DEBUG_OSPF_NSSA)
                        zlog_debug("%s: Processing Type-7", __func__);

        /* Stay away from any Local Translated Type-7 LSAs */
        if (CHECK_FLAG(lsa->flags, OSPF_LSA_LOCAL_XLT)) {
                if (IS_DEBUG_OSPF_NSSA)
                        zlog_debug("%s: Rejecting Local Xlt'd", __func__);
                return 0;
        }

        if (IS_DEBUG_OSPF(lsa, LSA)) {
                zlog_debug(
                        "Route[External]: Calculate AS-external-LSA to %pI4/%d adv_router %pI4",
                        &al->header.id, ip_masklen(al->mask),
                        &al->header.adv_router);
        }

        /* (1) If the cost specified by the LSA is LSInfinity, or if the
               LSA's LS age is equal to MaxAge, then examine the next LSA. */
        if ((metric = GET_METRIC(al->e[0].metric)) >= OSPF_LS_INFINITY) {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug(
                                "Route[External]: Metric is OSPF_LS_INFINITY");
                return 0;
        }
        if (IS_LSA_MAXAGE(lsa)) {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug(
                                "Route[External]: AS-external-LSA is MAXAGE");
                return 0;
        }

        /* (2) If the LSA was originated by the calculating router itself,
           examine the next LSA. */
        if (IS_LSA_SELF(lsa)) {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug(
                                "Route[External]: AS-external-LSA is self originated");
                return 0;
        }

        /* (3) Call the destination described by the LSA N.  N's address is
               obtained by masking the LSA's Link State ID with the
               network/subnet mask contained in the body of the LSA.  Look
               up the routing table entries (potentially one per attached
               area) for the AS boundary router (ASBR) that originated the
               LSA. If no entries exist for router ASBR (i.e., ASBR is
               unreachable), do nothing with this LSA and consider the next
               in the list. */

        asbr.family = AF_INET;
        asbr.prefix = al->header.adv_router;
        asbr.prefixlen = IPV4_MAX_BITLEN;
        apply_mask_ipv4(&asbr);

        asbr_route = ospf_find_asbr_route(ospf, ospf->new_rtrs, &asbr);
        if (asbr_route == NULL) {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug(
                                "Route[External]: Can't find originating ASBR route");
                return 0;
        }
        if (!(asbr_route->u.std.flags & ROUTER_LSA_EXTERNAL)) {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug(
                                "Route[External]: Originating router is not an ASBR");
                return 0;
        }

        /* Type-5 shouldn't be calculated if it is originated from NSSA ASBR.
         * As per RFC 3101, expectation is to receive type-7 lsas from
         * NSSA ASBR. Ignore calculation, if the current LSA is type-5 and
         * originated ASBR's area is NSSA.
         */
        if ((lsa->data->type == OSPF_AS_EXTERNAL_LSA)
            && (asbr_route->u.std.external_routing != OSPF_AREA_DEFAULT)) {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug(
                                "Route[External]: Ignore, If type-5 LSA from NSSA area.");
                return 0;
        }

        /*     Else, this LSA describes an AS external path to destination
               N.  Examine the forwarding address specified in the AS-
               external-LSA.  This indicates the IP address to which
               packets for the destination should be forwarded. */

        if (al->e[0].fwd_addr.s_addr == INADDR_ANY) {
                /* If the forwarding address is set to 0.0.0.0, packets should
                   be sent to the ASBR itself. Among the multiple routing table
                   entries for the ASBR, select the preferred entry as follows.
                   If RFC1583Compatibility is set to "disabled", prune the set
                   of routing table entries for the ASBR as described in
                   Section 16.4.1. In any case, among the remaining routing
                   table entries, select the routing table entry with the least
                   cost; when there are multiple least cost routing table
                   entries the entry whose associated area has the largest OSPF
                   Area ID (when considered as an unsigned 32-bit integer) is
                   chosen. */

                /* asbr_route already contains the requested route */
        } else {
                /* If the forwarding address is non-zero, look up the
                   forwarding address in the routing table.[24] The matching
                   routing table entry must specify an intra-area or inter-area
                   path; if no such path exists, do nothing with the LSA and
                   consider the next in the list. */
                if (!ospf_ase_forward_address_check(ospf, al->e[0].fwd_addr)) {
                        if (IS_DEBUG_OSPF(lsa, LSA))
                                zlog_debug(
                                        "Route[External]: Forwarding address is our router address");
                        return 0;
                }

                asbr.family = AF_INET;
                asbr.prefix = al->e[0].fwd_addr;
                asbr.prefixlen = IPV4_MAX_BITLEN;

                rn = route_node_match(ospf->new_table, (struct prefix *)&asbr);

                if (rn == NULL || (asbr_route = rn->info) == NULL) {
                        if (IS_DEBUG_OSPF(lsa, LSA))
                                zlog_debug(
                                        "Route[External]: Can't find route to forwarding address");
                        if (rn)
                                route_unlock_node(rn);
                        return 0;
                }

                route_unlock_node(rn);
        }

        /* (4) Let X be the cost specified by the preferred routing table
               entry for the ASBR/forwarding address, and Y the cost
               specified in the LSA.  X is in terms of the link state
               metric, and Y is a type 1 or 2 external metric. */


        /* (5) Look up the routing table entry for the destination N.  If
               no entry exists for N, install the AS external path to N,
               with next hop equal to the list of next hops to the
               forwarding address, and advertising router equal to ASBR.
               If the external metric type is 1, then the path-type is set
               to type 1 external and the cost is equal to X+Y.  If the
               external metric type is 2, the path-type is set to type 2
               external, the link state component of the route's cost is X,
               and the type 2 cost is Y. */
        new = ospf_ase_calculate_new_route(lsa, asbr_route, metric);

        /* (6) Compare the AS external path described by the LSA with the
               existing paths in N's routing table entry, as follows. If
               the new path is preferred, it replaces the present paths in
               N's routing table entry.  If the new path is of equal
               preference, it is added to N's routing table entry's list of
               paths. */

        /* Set prefix. */
        p.family = AF_INET;
        p.prefix = al->header.id;
        p.prefixlen = ip_masklen(al->mask);

        /* if there is a Intra/Inter area route to the N
           do not install external route */
        if ((rn = route_node_lookup(ospf->new_table, (struct prefix *)&p))) {
                route_unlock_node(rn);
                if (rn->info == NULL)
                        zlog_info("Route[External]: rn->info NULL");
                if (new)
                        ospf_route_free(new);
                return 0;
        }
        /* Find a route to the same dest */
        /* If there is no route, create new one. */
        if ((rn = route_node_lookup(ospf->new_external_route,
                                    (struct prefix *)&p)))
                route_unlock_node(rn);

        if (!rn || (or = rn->info) == NULL) {
                if (IS_DEBUG_OSPF(lsa, LSA))
                        zlog_debug("Route[External]: Adding a new route %pFX with paths %u",
                                   &p, listcount(asbr_route->paths));

                ospf_route_add(ospf->new_external_route, &p, new, asbr_route);

                if (al->e[0].fwd_addr.s_addr != INADDR_ANY)
                        ospf_ase_complete_direct_routes(new, al->e[0].fwd_addr);
                return 0;
        } else {
                /* (a) Intra-area and inter-area paths are always preferred
                       over AS external paths.

                   (b) Type 1 external paths are always preferred over type 2
                       external paths. When all paths are type 2 external
                       paths, the paths with the smallest advertised type 2
                       metric are always preferred. */
                ret = ospf_route_cmp(ospf, new, or);

                /*     (c) If the new AS external path is still
                   indistinguishable
                           from the current paths in the N's routing table
                   entry,
                           and RFC1583Compatibility is set to "disabled", select
                           the preferred paths based on the intra-AS paths to
                   the
                           ASBR/forwarding addresses, as specified in Section
                           16.4.1.

                       (d) If the new AS external path is still
                   indistinguishable
                           from the current paths in the N's routing table
                   entry,
                           select the preferred path based on a least cost
                           comparison.  Type 1 external paths are compared by
                           looking at the sum of the distance to the forwarding
                           address and the advertised type 1 metric (X+Y).  Type
                   2
                           external paths advertising equal type 2 metrics are
                           compared by looking at the distance to the forwarding
                           addresses.
                */
                /* New route is better */
                if (ret < 0) {
                        if (IS_DEBUG_OSPF(lsa, LSA))
                                zlog_debug(
                                        "Route[External]: New route is better");
                        ospf_route_subst(rn, new, asbr_route);
                        if (al->e[0].fwd_addr.s_addr != INADDR_ANY)
                                ospf_ase_complete_direct_routes(
                                        new, al->e[0].fwd_addr);
                        or = new;
                        new = NULL;
                }
                /* Old route is better */
                else if (ret > 0) {
                        if (IS_DEBUG_OSPF(lsa, LSA))
                                zlog_debug(
                                        "Route[External]: Old route is better");
                        /* do nothing */
                }
                /* Routes are equal */
                else {
                        if (IS_DEBUG_OSPF(lsa, LSA))
                                zlog_debug("Route[External]: Routes are equal");
                        ospf_route_copy_nexthops(or, asbr_route->paths);
                        if (al->e[0].fwd_addr.s_addr != INADDR_ANY)
                                ospf_ase_complete_direct_routes(
                                        or, al->e[0].fwd_addr);
                }
        }
        /* Make sure setting newly calculated ASBR route.*/
        or->u.ext.asbr = asbr_route;
        if (new)
                ospf_route_free(new);

        lsa->route = or ;
        return 0;
}

static int ospf_ase_route_match_same(struct route_table *rt,
                                     struct prefix *prefix,
                                     struct ospf_route *newor)
{
        struct route_node *rn;
        struct ospf_route *or;
        struct ospf_path *op;
        struct ospf_path *newop;
        struct listnode *n1;
        struct listnode *n2;

        if (!rt || !prefix)
                return 0;

        rn = route_node_lookup(rt, prefix);
        if (!rn)
                return 0;

        route_unlock_node(rn);

        or = rn->info;

        assert(or);

        if (or->path_type != newor->path_type)
                return 0;

        switch (or->path_type) {
        case OSPF_PATH_TYPE1_EXTERNAL:
                if (or->cost != newor->cost)
                        return 0;
                break;
        case OSPF_PATH_TYPE2_EXTERNAL:
                if ((or->cost != newor->cost)
                    || (or->u.ext.type2_cost != newor->u.ext.type2_cost))
                        return 0;
                break;
        default:
                assert(0);
                return 0;
        }

        assert(or->paths);

        if (or->paths->count != newor->paths->count)
                return 0;

        /* Check each path. */
        for (n1 = listhead(or->paths), n2 = listhead(newor->paths); n1 && n2;
             n1 = listnextnode_unchecked(n1), n2 = listnextnode_unchecked(n2)) {
                op = listgetdata(n1);
                newop = listgetdata(n2);

                if (!IPV4_ADDR_SAME(&op->nexthop, &newop->nexthop))
                        return 0;
                if (op->ifindex != newop->ifindex)
                        return 0;
        }

        if (or->u.ext.tag != newor->u.ext.tag)
                return 0;

        return 1;
}

static int ospf_ase_compare_tables(struct ospf *ospf,
                                   struct route_table *new_external_route,
                                   struct route_table *old_external_route)
{
        struct route_node *rn, *new_rn;
        struct ospf_route * or ;

        /* Remove deleted routes */
        for (rn = route_top(old_external_route); rn; rn = route_next(rn))
                if ((or = rn->info)) {
                        if (!(new_rn = route_node_lookup(new_external_route,
                                                         &rn->p)))
                                ospf_zebra_delete(
                                        ospf, (struct prefix_ipv4 *)&rn->p, or);
                        else
                                route_unlock_node(new_rn);
                }


        /* Install new routes */
        for (rn = route_top(new_external_route); rn; rn = route_next(rn))
                if ((or = rn->info) != NULL)
                        if (!ospf_ase_route_match_same(old_external_route,
                                                       &rn->p, or))
                                ospf_zebra_add(
                                        ospf, (struct prefix_ipv4 *)&rn->p, or);

        return 0;
}

static void ospf_ase_calculate_timer(struct thread *t)
{
        struct ospf *ospf;
        struct ospf_lsa *lsa;
        struct route_node *rn;
        struct listnode *node;
        struct ospf_area *area;
        struct timeval start_time, stop_time;

        ospf = THREAD_ARG(t);
        ospf->t_ase_calc = NULL;

        if (ospf->ase_calc) {
                ospf->ase_calc = 0;

                monotime(&start_time);

                /* Calculate external route for each AS-external-LSA */
                LSDB_LOOP (EXTERNAL_LSDB(ospf), rn, lsa)
                        ospf_ase_calculate_route(ospf, lsa);

                /*  This version simple adds to the table all NSSA areas  */
                if (ospf->anyNSSA)
                        for (ALL_LIST_ELEMENTS_RO(ospf->areas, node, area)) {
                                if (IS_DEBUG_OSPF_NSSA)
                                        zlog_debug("%s: looking at area %pI4",
                                                   __func__, &area->area_id);

                                if (area->external_routing == OSPF_AREA_NSSA)
                                        LSDB_LOOP (NSSA_LSDB(area), rn, lsa)
                                                ospf_ase_calculate_route(ospf,
                                                                         lsa);
                        }
                /* kevinm: And add the NSSA routes in ospf_top */
                LSDB_LOOP (NSSA_LSDB(ospf), rn, lsa)
                        ospf_ase_calculate_route(ospf, lsa);

                /* Compare old and new external routing table and install the
                   difference info zebra/kernel */
                ospf_ase_compare_tables(ospf, ospf->new_external_route,
                                        ospf->old_external_route);

                /* Delete old external routing table */
                ospf_route_table_free(ospf->old_external_route);
                ospf->old_external_route = ospf->new_external_route;
                ospf->new_external_route = route_table_init();

                monotime(&stop_time);

                if (IS_DEBUG_OSPF_EVENT)
                        zlog_info(
                                "SPF Processing Time(usecs): External Routes: %lld",
                                (stop_time.tv_sec - start_time.tv_sec)
                                                * 1000000LL
                                        + (stop_time.tv_usec
                                           - start_time.tv_usec));
        }

        /*
         * Uninstall remnant routes that were installed before the restart, but
         * that are no longer valid.
         */
        if (ospf->gr_info.finishing_restart) {
                ospf_zebra_gr_disable(ospf);
                ospf->gr_info.finishing_restart = false;
        }
}

void ospf_ase_calculate_schedule(struct ospf *ospf)
{
        if (ospf == NULL)
                return;

        ospf->ase_calc = 1;
}

void ospf_ase_calculate_timer_add(struct ospf *ospf)
{
        if (ospf == NULL)
                return;

        thread_add_timer(master, ospf_ase_calculate_timer, ospf,
                         OSPF_ASE_CALC_INTERVAL, &ospf->t_ase_calc);
}

void ospf_ase_register_external_lsa(struct ospf_lsa *lsa, struct ospf *top)
{
        struct route_node *rn;
        struct prefix_ipv4 p;
        struct list *lst;
        struct as_external_lsa *al;

        al = (struct as_external_lsa *)lsa->data;
        p.family = AF_INET;
        p.prefix = lsa->data->id;
        p.prefixlen = ip_masklen(al->mask);
        apply_mask_ipv4(&p);

        rn = route_node_get(top->external_lsas, (struct prefix *)&p);
        if ((lst = rn->info) == NULL)
                rn->info = lst = list_new();
        else
                route_unlock_node(rn);

        /* We assume that if LSA is deleted from DB
           is is also deleted from this RT */
        listnode_add(lst, ospf_lsa_lock(lsa)); /* external_lsas lst */
}

void ospf_ase_unregister_external_lsa(struct ospf_lsa *lsa, struct ospf *top)
{
        struct route_node *rn;
        struct prefix_ipv4 p;
        struct list *lst;
        struct as_external_lsa *al;

        al = (struct as_external_lsa *)lsa->data;
        p.family = AF_INET;
        p.prefix = lsa->data->id;
        p.prefixlen = ip_masklen(al->mask);
        apply_mask_ipv4(&p);

        rn = route_node_lookup(top->external_lsas, (struct prefix *)&p);

        if (rn) {
                lst = rn->info;
                struct listnode *node = listnode_lookup(lst, lsa);
                /* Unlock lsa only if node is present in the list */
                if (node) {
                        listnode_delete(lst, lsa);
                        ospf_lsa_unlock(&lsa); /* external_lsas list */
                }

                route_unlock_node(rn);
        }
}

void ospf_ase_external_lsas_finish(struct route_table *rt)
{
        struct route_node *rn;
        struct ospf_lsa *lsa;
        struct list *lst;
        struct listnode *node, *nnode;

        for (rn = route_top(rt); rn; rn = route_next(rn))
                if ((lst = rn->info) != NULL) {
                        for (ALL_LIST_ELEMENTS(lst, node, nnode, lsa))
                                ospf_lsa_unlock(&lsa); /* external_lsas lst */
                        list_delete(&lst);
                }

        route_table_finish(rt);
}

void ospf_ase_incremental_update(struct ospf *ospf, struct ospf_lsa *lsa)
{
        struct list *lsas;
        struct listnode *node;
        struct route_node *rn, *rn2;
        struct prefix_ipv4 p;
        struct route_table *tmp_old;
        struct as_external_lsa *al;

        al = (struct as_external_lsa *)lsa->data;
        p.family = AF_INET;
        p.prefix = lsa->data->id;
        p.prefixlen = ip_masklen(al->mask);
        apply_mask_ipv4(&p);

        /* if new_table is NULL, there was no spf calculation, thus
           incremental update is unneeded */
        if (!ospf->new_table)
                return;

        /* If there is already an intra-area or inter-area route
           to the destination, no recalculation is necessary
           (internal routes take precedence). */

        rn = route_node_lookup(ospf->new_table, (struct prefix *)&p);
        if (rn) {
                route_unlock_node(rn);
                if (rn->info)
                        return;
        }

        rn = route_node_lookup(ospf->external_lsas, (struct prefix *)&p);
        assert(rn);
        assert(rn->info);
        lsas = rn->info;
        route_unlock_node(rn);

        for (ALL_LIST_ELEMENTS_RO(lsas, node, lsa))
                ospf_ase_calculate_route(ospf, lsa);

        /* prepare temporary old routing table for compare */
        tmp_old = route_table_init();
        rn = route_node_lookup(ospf->old_external_route, (struct prefix *)&p);
        if (rn && rn->info) {
                rn2 = route_node_get(tmp_old, (struct prefix *)&p);
                rn2->info = rn->info;
                route_unlock_node(rn);
        }

        /* install changes to zebra */
        ospf_ase_compare_tables(ospf, ospf->new_external_route, tmp_old);

        /* update ospf->old_external_route table */
        if (rn && rn->info)
                ospf_route_free((struct ospf_route *)rn->info);

        rn2 = route_node_lookup(ospf->new_external_route, (struct prefix *)&p);
        /* if new route exists, install it to ospf->old_external_route */
        if (rn2 && rn2->info) {
                if (!rn)
                        rn = route_node_get(ospf->old_external_route,
                                            (struct prefix *)&p);
                rn->info = rn2->info;
        } else {
                /* remove route node from ospf->old_external_route */
                if (rn) {
                        rn->info = NULL;
                        route_unlock_node(rn);
                }
        }

        if (rn2) {
                /* rn2->info is stored in route node of ospf->old_external_route
                 */
                rn2->info = NULL;
                route_unlock_node(rn2);
                route_unlock_node(rn2);
        }

        route_table_finish(tmp_old);
}