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;
26 final class BestPathSelector {
27 private static final Collection<PathArgument> ORIGINATOR_ID = ImmutableList.<PathArgument>of(new NodeIdentifier(OriginatorId.QNAME), new NodeIdentifier(QName.create(OriginatorId.QNAME, "originator")));
29 private final Long ourAs;
30 private UnsignedInteger bestOriginatorId = null;
31 private UnsignedInteger bestRouterId = null;
32 private BestPathState bestState = null;
34 BestPathSelector(final Long ourAs) {
35 this.ourAs = Preconditions.checkNotNull(ourAs);
38 void processPath(final UnsignedInteger routerId, final ContainerNode attrs) {
39 Preconditions.checkNotNull(routerId, "Router ID may not be null");
41 // Consider only non-null attributes
44 * RFC 4456 mandates the use of Originator IDs instead of Router ID for
47 final Optional<NormalizedNode<?, ?>> maybeOriginatorId = NormalizedNodes.findNode(attrs, ORIGINATOR_ID);
48 final UnsignedInteger originatorId;
49 if (maybeOriginatorId.isPresent()) {
50 originatorId = RouterIds.routerIdForAddress((String) ((LeafNode<?>)maybeOriginatorId.get()).getValue());
52 originatorId = routerId;
56 * Store the new details if we have nothing stored or when the selection algorithm indicates new details
59 final BestPathState state = new BestPathState(attrs);
60 if (this.bestOriginatorId == null || selectPath(originatorId, state)) {
61 this.bestOriginatorId = originatorId;
62 this.bestRouterId = routerId;
63 this.bestState = state;
69 return this.bestRouterId == null ? null : new BestPath(this.bestRouterId, this.bestState);
73 * Chooses best route according to BGP best path selection.
75 * @param originatorId of the new route
76 * @param state attributes of the new route
77 * @return true if the existing path is better, false if the new path is better
79 private boolean selectPath(@Nonnull final UnsignedInteger originatorId, @Nonnull final BestPathState state) {
80 // 1. prefer path with accessible nexthop
81 // - we assume that all nexthops are accessible
84 * 2. prefer path with higher LOCAL_PREF
86 * FIXME: for eBGP cases (when the LOCAL_PREF is missing), we should assign a policy-based preference
87 * before we ever get here.
89 if (this.bestState.getLocalPref() == null && state.getLocalPref() != null) {
92 if (this.bestState.getLocalPref() != null && state.getLocalPref() == null) {
95 if (state.getLocalPref() != null && state.getLocalPref() > this.bestState.getLocalPref()) {
99 // 3. prefer learned path
100 // - we assume that all paths are learned
102 // 4. prefer the path with the shortest AS_PATH.
103 if (this.bestState.getAsPathLength() > state.getAsPathLength()) {
107 // 5. prefer the path with the lowest origin type
108 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
109 if (!this.bestState.getOrigin().equals(state.getOrigin())) {
110 final BgpOrigin bo = this.bestState.getOrigin();
111 final BgpOrigin no = state.getOrigin();
113 // This trick relies on the order in which the values are declared in the model.
114 if (no.ordinal() < bo.ordinal()) {
119 // FIXME: we should be able to cache the best AS
120 final Long bestAs = this.bestState.getPeerAs();
121 final Long newAs = state.getPeerAs();
124 * Checks 6 and 7 are mutually-exclusive, as MEDs are comparable
125 * only when the routes originated from the same AS. On the other
126 * hand, when they are from the same AS, they are in the same iBGP/eBGP
130 if (bestAs.equals(newAs)) {
131 // 6. prefer the path with the lowest multi-exit discriminator (MED)
132 if (this.bestState.getMultiExitDisc() != null || state.getMultiExitDisc() != null) {
133 final Long bmed = this.bestState.getMultiExitDisc();
134 final Long nmed = state.getMultiExitDisc();
141 * 7. prefer eBGP over iBGP paths
143 * EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System),
144 * so we just compare the AS numbers to our AS.
146 * FIXME: we should know this information from the peer directly.
148 if (!this.ourAs.equals(bestAs) && this.ourAs.equals(newAs)) {
153 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
154 // - no next hop metric is advertised
157 * 9. When both paths are external, prefer the path that was received first (the oldest one).
159 * FIXME: we do not want to store an explicit timer for each set due to performance/memory
160 * constraints. Our caller has the information about which attributes have changed
161 * since the selection process has ran last time, which may be a good enough approximation,
162 * but its properties need to be analyzed.
166 * 10. Prefer the route that comes from the BGP router with the lowest router ID.
168 * This is normally guaranteed by the iteration order of our caller, which runs selection
169 * in the order of increasing router ID, but RFC-4456 Route Reflection throws a wrench into that.
171 * With RFC-5004, this gets a bit easier, because it completely eliminates step f) and later :-)
173 * RFC-5004 states that this algorithm should end here and select existing path over new path in the
174 * best path selection process. Benefits are listed in the RFC: @see http://tools.ietf.org/html/rfc500
175 * - This algorithm SHOULD NOT be applied when either path is from a BGP Confederation peer.
176 * - not applicable, we don't deal with confederation peers
177 * - The algorithm SHOULD NOT be applied when both paths are from peers with an identical BGP identifier
178 * (i.e., there exist parallel BGP sessions between two BGP speakers).
179 * - not applicable, BUG-2631 prevents parallel sessions to be created.