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.base.Optional;
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.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.rev130919.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.<YangInstanceIdentifier.PathArgument>of(new
28 YangInstanceIdentifier.NodeIdentifier(OriginatorId.QNAME), new YangInstanceIdentifier.NodeIdentifier(QName.create(OriginatorId.QNAME, "originator")));
30 private final Long ourAs;
31 protected UnsignedInteger bestOriginatorId = null;
32 protected BestPathState bestState = null;
34 protected AbstractBestPathSelector(final Long ourAs) {
39 * RFC 4456 mandates the use of Originator IDs instead of Router ID for
41 * @param routerId routerID
42 * @param attrs router attributes
43 * @return returns originators Id if present otherwise routerId
45 protected UnsignedInteger replaceOriginator(final UnsignedInteger routerId, final ContainerNode attrs) {
46 final Optional<NormalizedNode<?, ?>> maybeOriginatorId = NormalizedNodes.findNode(attrs, ORIGINATOR_ID);
47 if (maybeOriginatorId.isPresent()) {
48 return RouterIds.routerIdForAddress((String) maybeOriginatorId.get().getValue());
55 * Chooses best route according to BGP best path selection.
57 * @param state attributes of the new route
58 * @return true if the existing path is better, false if the new path is better
60 protected boolean isExistingPathBetter(@Nonnull final BestPathState state) {
61 // 1. prefer path with accessible nexthop
62 // - we assume that all nexthops are accessible
64 * 2. prefer path with higher LOCAL_PREF
66 * FIXME: for eBGP cases (when the LOCAL_PREF is missing), we should assign a policy-based preference
67 * before we ever get here.
69 if (this.bestState.getLocalPref() == null && state.getLocalPref() != null) {
72 if (this.bestState.getLocalPref() != null && state.getLocalPref() == null) {
75 if (state.getLocalPref() != null && state.getLocalPref() > this.bestState.getLocalPref()) {
78 if (state.getLocalPref() != null && state.getLocalPref() < this.bestState.getLocalPref()) {
81 // 3. prefer learned path
82 // - we assume that all paths are learned
84 // 4. prefer the path with the shortest AS_PATH.
85 if (this.bestState.getAsPathLength() != state.getAsPathLength()) {
86 return this.bestState.getAsPathLength() < state.getAsPathLength();
89 // 5. prefer the path with the lowest origin type
90 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
91 if (!this.bestState.getOrigin().equals(state.getOrigin())) {
92 final BgpOrigin bo = this.bestState.getOrigin();
93 final BgpOrigin no = state.getOrigin();
95 // This trick relies on the order in which the values are declared in the model.
96 return no.ordinal() > bo.ordinal();
98 // FIXME: we should be able to cache the best AS
99 final Long bestAs = this.bestState.getPeerAs();
100 final Long newAs = state.getPeerAs();
103 * Checks 6 and 7 are mutually-exclusive, as MEDs are comparable
104 * only when the routes originated from the same AS. On the other
105 * hand, when they are from the same AS, they are in the same iBGP/eBGP
109 if (bestAs.equals(newAs)) {
110 // 6. prefer the path with the lowest multi-exit discriminator (MED)
111 if (this.bestState.getMultiExitDisc() != null || state.getMultiExitDisc() != null) {
112 final Long bmed = this.bestState.getMultiExitDisc();
113 final Long nmed = state.getMultiExitDisc();
118 * 7. prefer eBGP over iBGP paths
120 * EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System),
121 * so we just compare the AS numbers to our AS.
123 * FIXME: we should know this information from the peer directly.
125 if (!this.ourAs.equals(bestAs) && this.ourAs.equals(newAs)) {
130 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
131 // - no next hop metric is advertised
134 * 9. When both paths are external, prefer the path that was received first (the oldest one).
136 * FIXME: we do not want to store an explicit timer for each set due to performance/memory
137 * constraints. Our caller has the information about which attributes have changed
138 * since the selection process has ran last time, which may be a good enough approximation,
139 * but its properties need to be analyzed.
143 * 10. Prefer the route that comes from the BGP router with the lowest router ID.
145 * This is normally guaranteed by the iteration order of our caller, which runs selection
146 * in the order of increasing router ID, but RFC-4456 Route Reflection throws a wrench into that.
148 * With RFC-5004, this gets a bit easier, because it completely eliminates step f) and later :-)
150 * RFC-5004 states that this algorithm should end here and select existing path over new path in the
151 * best path selection process. Benefits are listed in the RFC: @see http://tools.ietf.org/html/rfc500
152 * - This algorithm SHOULD NOT be applied when either path is from a BGP Confederation peer.
153 * - not applicable, we don't deal with confederation peers
154 * - The algorithm SHOULD NOT be applied when both paths are from peers with an identical BGP identifier
155 * (i.e., there exist parallel BGP sessions between two BGP speakers).
156 * - not applicable, BUG-2631 prevents parallel sessions to be created.