/* $OpenBSD: rde_decide.c,v 1.41 2005/04/12 14:32:01 claudio Exp $ */ /* * Copyright (c) 2003, 2004 Claudio Jeker * Copyright (c) 2003, 2004 Henning Brauer * * Permission to use, copy, modify, and distribute this software for any * purpose with or without fee is hereby granted, provided that the above * copyright notice and this permission notice appear in all copies. * * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ #include #include #include #include "bgpd.h" #include "rde.h" int prefix_cmp(struct prefix *, struct prefix *); /* * Decision Engine RFC implementation: * Phase 1: * - calculate LOCAL_PREF if needed -- EBGP or IGP learnt routes * - IBGP routes may either use LOCAL_PREF or the local system computes * the degree of preference * - If the route is ineligible, the route MAY NOT serve as an input to * the next phase of route selection * - if the route is eligible the computed value MUST be used as the * LOCAL_PREF value in any IBGP readvertisement * * Phase 2: * - If the NEXT_HOP attribute of a BGP route depicts an address that is * not resolvable the BGP route MUST be excluded from the Phase 2 decision * function. * - If the AS_PATH attribute of a BGP route contains an AS loop, the BGP * route should be excluded from the Phase 2 decision function. * - The local BGP speaker identifies the route that has: * a) the highest degree of preference of any route to the same set * of destinations * b) is the only route to that destination * c) is selected as a result of the Phase 2 tie breaking rules * - The local speaker MUST determine the immediate next-hop address from * the NEXT_HOP attribute of the selected route. * - If either the immediate next hop or the IGP cost to the NEXT_HOP changes, * Phase 2 Route Selection MUST be performed again. * * Route Resolvability Condition * - A route Rte1, referencing only the intermediate network address, is * considered resolvable if the Routing Table contains at least one * resolvable route Rte2 that matches Rte1's intermediate network address * and is not recursively resolved through Rte1. * - Routes referencing interfaces are considered resolvable if the state of * the referenced interface is up and IP processing is enabled. * * Breaking Ties (Phase 2) * 1. Remove from consideration all routes which are not tied for having the * smallest number of AS numbers present in their AS_PATH attributes. * Note, that when counting this number, an AS_SET counts as 1 * 2. Remove from consideration all routes which are not tied for having the * lowest Origin number in their Origin attribute. * 3. Remove from consideration routes with less-preferred MULTI_EXIT_DISC * attributes. MULTI_EXIT_DISC is only comparable between routes learned * from the same neighboring AS. * 4. If at least one of the candidate routes was received via EBGP, * remove from consideration all routes which were received via IBGP. * 5. Remove from consideration any routes with less-preferred interior cost. * If the NEXT_HOP hop for a route is reachable, but no cost can be * determined, then this step should be skipped. * 6. Remove from consideration all routes other than the route that was * advertised by the BGP speaker whose BGP Identifier has the lowest value. * 7. Prefer the route received from the lowest peer address. * * Phase 3: Route Dissemination * - All routes in the Loc-RIB are processed into Adj-RIBs-Out according * to configured policy. A route SHALL NOT be installed in the Adj-Rib-Out * unless the destination and NEXT_HOP described by this route may be * forwarded appropriately by the Routing Table. */ /* * Decision Engine OUR implementation: * Our implementation has only one RIB. The filtering is done first. The * filtering calculates the preference and stores it in LOCAL_PREF (Phase 1). * Ineligible routes are flagged as ineligible via nexthop_add(). * Phase 3 is done together with Phase 2. * In following cases a prefix needs to be reevaluated: * - update of a prefix (path_update) * - withdraw of a prefix (prefix_remove) * - state change of the nexthop (nexthop-{in}validate) * - state change of session (session down) */ /* * Compare two prefixes with equal pt_entry. Returns an integer greater than or * less than 0, according to whether the prefix p1 is more or less preferred * than the prefix p2. p1 should be used for the new prefix and p2 for a * already added prefix. */ int prefix_cmp(struct prefix *p1, struct prefix *p2) { struct rde_aspath *asp1, *asp2; if (p1 == NULL) return (-1); if (p2 == NULL) return (1); asp1 = p1->aspath; asp2 = p2->aspath; /* 1. check if prefix is eligible a.k.a reachable */ if (asp2->nexthop != NULL && asp2->nexthop->state != NEXTHOP_REACH) return (1); if (asp1->nexthop != NULL && asp1->nexthop->state != NEXTHOP_REACH) return (-1); /* 2. preference of prefix, bigger is better */ if ((asp1->lpref - asp2->lpref) != 0) return (asp1->lpref - asp2->lpref); /* 3. aspath count, the shorter the better */ if ((asp2->aspath->ascnt - asp1->aspath->ascnt) != 0) return (asp2->aspath->ascnt - asp1->aspath->ascnt); /* 4. origin, the lower the better */ if ((asp2->origin - asp1->origin) != 0) return (asp2->origin - asp1->origin); /* 5. MED decision, only comparable between the same neighboring AS */ if (aspath_neighbor(asp1->aspath) == aspath_neighbor(asp2->aspath)) /* lowest value wins */ if ((asp2->med - asp1->med) != 0) return (asp2->med - asp1->med); /* * 6. EBGP is cooler than IBGP * It is absolutely important that the ebgp value in peer_config.ebgp * is bigger than all other ones (IBGP, confederations) */ if ((asp1->peer->conf.ebgp - asp2->peer->conf.ebgp) != 0) { if (asp1->peer->conf.ebgp == 1) /* p1 is EBGP other is lower */ return 1; else if (asp2->peer->conf.ebgp == 1) /* p2 is EBGP */ return -1; } /* * 7. local tie-breaker, this weight is here to tip equal long AS * pathes in one or the other direction. It happens more and more * that AS pathes are equally long and so traffic engineering needs * a metric that weights a prefix at a very late stage in the * decision process. */ if ((asp1->weight - asp2->weight) != 0) return (asp1->weight - asp2->weight); /* 8. nexthop costs. NOT YET -> IGNORE */ /* * 9. older route (more stable) wins but only if route-age * evaluation is enabled. */ if (rde_decisionflags() & BGPD_FLAG_DECISION_ROUTEAGE) if ((p2->lastchange - p1->lastchange) != 0) return (p2->lastchange - p1->lastchange); /* 10. lowest BGP Id wins */ if ((p2->peer->remote_bgpid - p1->peer->remote_bgpid) != 0) return (p2->peer->remote_bgpid - p1->peer->remote_bgpid); /* 11. lowest peer address wins (IPv4 is better than IPv6) */ if (memcmp(&p1->peer->remote_addr, &p2->peer->remote_addr, sizeof(p1->peer->remote_addr)) != 0) return (-memcmp(&p1->peer->remote_addr, &p2->peer->remote_addr, sizeof(p1->peer->remote_addr))); fatalx("Uh, oh a politician in the decision process"); /* NOTREACHED */ return (0); } /* * Find the correct place to insert the prefix in the prefix list. * If the active prefix has changed we need to send an update. * The to evaluate prefix must not be in the prefix list. */ void prefix_evaluate(struct prefix *p, struct pt_entry *pte) { struct prefix *xp; if (rde_noevaluate()) { /* decision process is turned off */ if (p != NULL) LIST_INSERT_HEAD(&pte->prefix_h, p, prefix_l); if (pte->active != NULL) pte->active = NULL; return; } if (p != NULL) { if (LIST_EMPTY(&pte->prefix_h)) LIST_INSERT_HEAD(&pte->prefix_h, p, prefix_l); else { LIST_FOREACH(xp, &pte->prefix_h, prefix_l) if (prefix_cmp(p, xp) > 0) { LIST_INSERT_BEFORE(xp, p, prefix_l); break; } else if (LIST_NEXT(xp, prefix_l) == NULL) { /* if xp last element ... */ LIST_INSERT_AFTER(xp, p, prefix_l); break; } } } xp = LIST_FIRST(&pte->prefix_h); if (pte->active != xp) { /* need to generate an update */ if (pte->active != NULL) pte->active->aspath->active_cnt--; /* * Send update with remove for pte->active and add for xp * but remember that xp may be ineligible or NULL. * Do not send an update if the only available path * has an unreachable nexthop. This decision has to be made * by the called functions. */ rde_generate_updates(xp, pte->active); rde_send_kroute(xp, pte->active); if (xp == NULL || (xp->aspath->nexthop != NULL && xp->aspath->nexthop->state != NEXTHOP_REACH)) pte->active = NULL; else { pte->active = xp; pte->active->aspath->active_cnt++; } } }