2 * Copyright (c) 2016 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
9 package org.opendaylight.protocol.bgp.mode.spi;
11 import com.google.common.collect.ImmutableList;
12 import com.google.common.primitives.UnsignedInteger;
13 import java.util.Collection;
14 import java.util.Optional;
15 import javax.annotation.Nonnull;
16 import org.opendaylight.protocol.bgp.mode.api.BestPathState;
17 import org.opendaylight.protocol.bgp.rib.spi.RouterIds;
18 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev171207.OriginatorId;
19 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.BgpOrigin;
20 import org.opendaylight.yangtools.yang.common.QName;
21 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
22 import org.opendaylight.yangtools.yang.data.api.schema.ContainerNode;
23 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
24 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNodes;
26 public class AbstractBestPathSelector {
27 private static final Collection<YangInstanceIdentifier.PathArgument> ORIGINATOR_ID = ImmutableList.of(new
28 YangInstanceIdentifier.NodeIdentifier(OriginatorId.QNAME),
29 new YangInstanceIdentifier.NodeIdentifier(QName.create(OriginatorId.QNAME, "originator")));
31 private final Long ourAs;
32 protected UnsignedInteger bestOriginatorId = null;
33 protected BestPathState bestState = null;
35 protected AbstractBestPathSelector(final Long ourAs) {
40 * RFC 4456 mandates the use of Originator IDs instead of Router ID for
42 * @param routerId routerID
43 * @param attrs router attributes
44 * @return returns originators Id if present otherwise routerId
46 protected UnsignedInteger replaceOriginator(final UnsignedInteger routerId, final ContainerNode attrs) {
47 final Optional<NormalizedNode<?, ?>> maybeOriginatorId = NormalizedNodes.findNode(attrs, ORIGINATOR_ID);
48 if (maybeOriginatorId.isPresent()) {
49 return RouterIds.routerIdForAddress((String) maybeOriginatorId.get().getValue());
56 * Chooses best route according to BGP best path selection.
58 * @param state attributes of the new route
59 * @return true if the existing path is better, false if the new path is better
61 protected boolean isExistingPathBetter(@Nonnull final BestPathState state) {
62 // 1. prefer path with accessible nexthop
63 // - we assume that all nexthops are accessible
65 * 2. prefer path with higher LOCAL_PREF
67 * FIXME: for eBGP cases (when the LOCAL_PREF is missing), we should assign a policy-based preference
68 * before we ever get here.
70 if (this.bestState.getLocalPref() == null && state.getLocalPref() != null) {
73 if (this.bestState.getLocalPref() != null && state.getLocalPref() == null) {
76 if (state.getLocalPref() != null && state.getLocalPref() > this.bestState.getLocalPref()) {
79 if (state.getLocalPref() != null && state.getLocalPref() < this.bestState.getLocalPref()) {
82 // 3. prefer learned path
83 // - we assume that all paths are learned
85 // 4. prefer the path with the shortest AS_PATH.
86 if (this.bestState.getAsPathLength() != state.getAsPathLength()) {
87 return this.bestState.getAsPathLength() < state.getAsPathLength();
90 // 5. prefer the path with the lowest origin type
91 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
92 if (!this.bestState.getOrigin().equals(state.getOrigin())) {
93 final BgpOrigin bo = this.bestState.getOrigin();
94 final BgpOrigin no = state.getOrigin();
96 // This trick relies on the order in which the values are declared in the model.
97 return no.ordinal() > bo.ordinal();
99 // FIXME: we should be able to cache the best AS
100 final Long bestAs = this.bestState.getPeerAs();
101 final Long newAs = state.getPeerAs();
104 * Checks 6 and 7 are mutually-exclusive, as MEDs are comparable
105 * only when the routes originated from the same AS. On the other
106 * hand, when they are from the same AS, they are in the same iBGP/eBGP
110 if (bestAs.equals(newAs)) {
111 // 6. prefer the path with the lowest multi-exit discriminator (MED)
112 if (this.bestState.getMultiExitDisc() != null || state.getMultiExitDisc() != null) {
113 final Long bmed = this.bestState.getMultiExitDisc();
114 final Long nmed = state.getMultiExitDisc();
119 * 7. prefer eBGP over iBGP paths
121 * EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System),
122 * so we just compare the AS numbers to our AS.
124 * FIXME: we should know this information from the peer directly.
126 if (!this.ourAs.equals(bestAs) && this.ourAs.equals(newAs)) {
131 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
132 // - no next hop metric is advertised
135 * 9. When both paths are external, prefer the path that was received first (the oldest one).
137 * FIXME: we do not want to store an explicit timer for each set due to performance/memory
138 * constraints. Our caller has the information about which attributes have changed
139 * since the selection process has ran last time, which may be a good enough approximation,
140 * but its properties need to be analyzed.
144 * 10. Prefer the route that comes from the BGP router with the lowest router ID.
146 * This is normally guaranteed by the iteration order of our caller, which runs selection
147 * in the order of increasing router ID, but RFC-4456 Route Reflection throws a wrench into that.
149 * With RFC-5004, this gets a bit easier, because it completely eliminates step f) and later :-)
151 * RFC-5004 states that this algorithm should end here and select existing path over new path in the
152 * best path selection process. Benefits are listed in the RFC: @see http://tools.ietf.org/html/rfc500
153 * - This algorithm SHOULD NOT be applied when either path is from a BGP Confederation peer.
154 * - not applicable, we don't deal with confederation peers
155 * - The algorithm SHOULD NOT be applied when both paths are from peers with an identical BGP identifier
156 * (i.e., there exist parallel BGP sessions between two BGP speakers).
157 * - not applicable, BUG-2631 prevents parallel sessions to be created.