2 * Copyright (c) 2015 Cisco Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
8 package org.opendaylight.protocol.bgp.rib.impl;
10 import com.google.common.base.Optional;
11 import com.google.common.base.Preconditions;
12 import com.google.common.collect.ImmutableList;
13 import com.google.common.primitives.UnsignedInteger;
14 import java.util.Collection;
15 import javax.annotation.Nonnull;
16 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.OriginatorId;
17 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.BgpOrigin;
18 import org.opendaylight.yangtools.yang.common.QName;
19 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.NodeIdentifier;
20 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
21 import org.opendaylight.yangtools.yang.data.api.schema.ContainerNode;
22 import org.opendaylight.yangtools.yang.data.api.schema.LeafNode;
23 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
24 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNodes;
25 import org.slf4j.Logger;
26 import org.slf4j.LoggerFactory;
28 final class BestPathSelector {
29 private static final Logger LOG = LoggerFactory.getLogger(BestPathSelector.class);
30 private static final Collection<PathArgument> ORIGINATOR_ID = ImmutableList.<PathArgument>of(new NodeIdentifier(OriginatorId.QNAME), new NodeIdentifier(QName.create(OriginatorId.QNAME, "originator")));
32 private final Long ourAs;
33 private UnsignedInteger bestOriginatorId = null;
34 private UnsignedInteger bestRouterId = null;
35 private BestPathState bestState = null;
37 BestPathSelector(final Long ourAs) {
38 this.ourAs = Preconditions.checkNotNull(ourAs);
41 void processPath(final UnsignedInteger routerId, final ContainerNode attrs) {
42 Preconditions.checkNotNull(routerId, "Router ID may not be null");
44 // Consider only non-null attributes
47 * RFC 4456 mandates the use of Originator IDs instead of Router ID for
50 final Optional<NormalizedNode<?, ?>> maybeOriginatorId = NormalizedNodes.findNode(attrs, ORIGINATOR_ID);
51 final UnsignedInteger originatorId;
52 if (maybeOriginatorId.isPresent()) {
53 originatorId = RouterIds.routerIdForAddress((String) ((LeafNode<?>)maybeOriginatorId.get()).getValue());
55 originatorId = routerId;
59 * Store the new details if we have nothing stored or when the selection algorithm indicates new details
62 final BestPathState state = new BestPathState(attrs);
63 if (this.bestOriginatorId == null || !selectPath(originatorId, state)) {
64 LOG.trace("Selecting path from router {}", routerId);
65 this.bestOriginatorId = originatorId;
66 this.bestRouterId = routerId;
67 this.bestState = state;
73 return this.bestRouterId == null ? null : new BestPath(this.bestRouterId, this.bestState);
77 * Chooses best route according to BGP best path selection.
79 * @param originatorId of the new route
80 * @param state attributes of the new route
81 * @return true if the existing path is better, false if the new path is better
83 private boolean selectPath(@Nonnull final UnsignedInteger originatorId, @Nonnull final BestPathState state) {
84 // 1. prefer path with accessible nexthop
85 // - we assume that all nexthops are accessible
88 * 2. prefer path with higher LOCAL_PREF
90 * FIXME: for eBGP cases (when the LOCAL_PREF is missing), we should assign a policy-based preference
91 * before we ever get here.
93 if (this.bestState.getLocalPref() == null && state.getLocalPref() != null) {
96 if (this.bestState.getLocalPref() != null && state.getLocalPref() == null) {
99 if (state.getLocalPref() != null && state.getLocalPref() > this.bestState.getLocalPref()) {
103 // 3. prefer learned path
104 // - we assume that all paths are learned
106 // 4. prefer the path with the shortest AS_PATH.
107 if (this.bestState.getAsPathLength() != state.getAsPathLength()) {
108 return this.bestState.getAsPathLength() < state.getAsPathLength();
111 // 5. prefer the path with the lowest origin type
112 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
113 if (!this.bestState.getOrigin().equals(state.getOrigin())) {
114 final BgpOrigin bo = this.bestState.getOrigin();
115 final BgpOrigin no = state.getOrigin();
117 // This trick relies on the order in which the values are declared in the model.
118 if (no.ordinal() < bo.ordinal()) {
123 // FIXME: we should be able to cache the best AS
124 final Long bestAs = this.bestState.getPeerAs();
125 final Long newAs = state.getPeerAs();
128 * Checks 6 and 7 are mutually-exclusive, as MEDs are comparable
129 * only when the routes originated from the same AS. On the other
130 * hand, when they are from the same AS, they are in the same iBGP/eBGP
134 if (bestAs.equals(newAs)) {
135 // 6. prefer the path with the lowest multi-exit discriminator (MED)
136 if (this.bestState.getMultiExitDisc() != null || state.getMultiExitDisc() != null) {
137 final Long bmed = this.bestState.getMultiExitDisc();
138 final Long nmed = state.getMultiExitDisc();
145 * 7. prefer eBGP over iBGP paths
147 * EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System),
148 * so we just compare the AS numbers to our AS.
150 * FIXME: we should know this information from the peer directly.
152 if (!this.ourAs.equals(bestAs) && this.ourAs.equals(newAs)) {
157 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
158 // - no next hop metric is advertised
161 * 9. When both paths are external, prefer the path that was received first (the oldest one).
163 * FIXME: we do not want to store an explicit timer for each set due to performance/memory
164 * constraints. Our caller has the information about which attributes have changed
165 * since the selection process has ran last time, which may be a good enough approximation,
166 * but its properties need to be analyzed.
170 * 10. Prefer the route that comes from the BGP router with the lowest router ID.
172 * This is normally guaranteed by the iteration order of our caller, which runs selection
173 * in the order of increasing router ID, but RFC-4456 Route Reflection throws a wrench into that.
175 * With RFC-5004, this gets a bit easier, because it completely eliminates step f) and later :-)
177 * RFC-5004 states that this algorithm should end here and select existing path over new path in the
178 * best path selection process. Benefits are listed in the RFC: @see http://tools.ietf.org/html/rfc500
179 * - This algorithm SHOULD NOT be applied when either path is from a BGP Confederation peer.
180 * - not applicable, we don't deal with confederation peers
181 * - The algorithm SHOULD NOT be applied when both paths are from peers with an identical BGP identifier
182 * (i.e., there exist parallel BGP sessions between two BGP speakers).
183 * - not applicable, BUG-2631 prevents parallel sessions to be created.