2 * Copyright (c) 2013 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.spi;
10 import com.google.common.annotations.VisibleForTesting;
11 import com.google.common.base.Preconditions;
12 import java.io.Serializable;
13 import java.util.Arrays;
14 import java.util.Comparator;
15 import java.util.List;
16 import org.opendaylight.protocol.bgp.rib.spi.AbstractAdjRIBs.RIBEntryData;
17 import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.inet.types.rev100924.AsNumber;
18 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.PathAttributes;
19 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.path.attributes.as.path.Segments;
20 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.BgpOrigin;
21 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.as.path.segment.c.segment.AListCase;
22 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.as.path.segment.c.segment.ASetCase;
25 * This comparator is intended to implement BGP Best Path Selection algorithm, as described at
27 * @see http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml
29 * @param <T> Actual object state reference
31 public final class BGPObjectComparator implements Comparator<RIBEntryData<?, ?, ?>>, Serializable {
33 private static final long serialVersionUID = 3299599519482155374L;
35 private final AsNumber ourAS;
37 public BGPObjectComparator(final AsNumber ourAs) {
38 this.ourAS = Preconditions.checkNotNull(ourAs);
42 public int compare(final RIBEntryData<?, ?, ?> newObject, final RIBEntryData<?, ?, ?> oldObject) {
43 if (newObject == oldObject) {
46 if (newObject == null) {
49 if (oldObject == null) {
53 final PathAttributes newPath = newObject.getPathAttributes();
54 final PathAttributes oldPath = oldObject.getPathAttributes();
55 if (newPath.equals(oldPath) && Arrays.equals(newObject.getPeer().getRawIdentifier(), oldObject.getPeer().getRawIdentifier())) {
59 // 1. prefer path with accessible nexthop
60 // - we assume that all nexthops are accessible
62 // 2. prefer path with higher LOCAL_PREF
63 if ((newPath.getLocalPref() != null || oldPath.getLocalPref() != null)
64 && (newPath.getLocalPref() != null && !newPath.getLocalPref().equals(oldPath.getLocalPref()))) {
65 return newPath.getLocalPref().getPref().compareTo(oldPath.getLocalPref().getPref());
68 // 3. prefer learned path
69 // - we assume that all paths are learned
71 // 4. prefer the path with the shortest AS_PATH.
72 if (!newPath.getAsPath().equals(oldPath.getAsPath())) {
73 final Integer i1 = countAsPath(newPath.getAsPath().getSegments());
74 final Integer i2 = countAsPath(oldPath.getAsPath().getSegments());
75 return i2.compareTo(i1);
78 // 5. prefer the path with the lowest origin type
79 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
80 if (!newPath.getOrigin().equals(oldPath.getOrigin())) {
81 if (newPath.getOrigin().getValue().equals(BgpOrigin.Igp)) {
84 if (oldPath.getOrigin().getValue().equals(BgpOrigin.Igp)) {
87 if (newPath.getOrigin().getValue().equals(BgpOrigin.Egp)) {
94 // 6. prefer the path with the lowest multi-exit discriminator (MED)
95 if ((newPath.getMultiExitDisc() != null || oldPath.getMultiExitDisc() != null)
96 && (newPath.getMultiExitDisc() != null && !newPath.getMultiExitDisc().equals(oldPath.getMultiExitDisc()))) {
97 return oldPath.getMultiExitDisc().getMed().compareTo(newPath.getMultiExitDisc().getMed());
100 // 7. prefer eBGP over iBGP paths
101 // EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System).
102 final AsNumber first = getPeerAs(newPath.getAsPath().getSegments());
103 final AsNumber second = getPeerAs(oldPath.getAsPath().getSegments());
104 if ((first != null || second != null) && (first != null && !first.equals(second))) {
105 if (first.equals(this.ourAS)) {
108 if (second == null || second.equals(this.ourAS)) {
113 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
114 // - no next hop metric is advertized
116 // 9. When both paths are external, prefer the path that was received first (the oldest one).
117 // if (first.equals(this.ourAS) && second.equals(this.ourAS)) {
118 // FIXME: do we have a way how to determine which one was received first?
120 // 10. Prefer the route that comes from the BGP router with the lowest router ID.
121 // The router ID is the highest IP address on the router, with preference given to loopback addresses.
122 // If a path contains route reflector (RR) attributes, the originator ID is substituted for the router ID in the
123 // path selection process.
125 // RFC5004 states that this algorithm should end here and select existing path over new path in the
126 // best path selection process. Benefits are listed in the RFC: @see http://tools.ietf.org/html/rfc500
127 // - This algorithm SHOULD NOT be applied when either path is from a BGP Confederation peer.
128 // - not applicable, we don't deal with confederation peers
129 // - The algorithm SHOULD NOT be applied when both paths are from peers with an identical BGP identifier (i.e., there exist parallel BGP sessions between two BGP speakers).
130 // - not applicable, BUG-2631 prevents parallel sessions to be created.
135 private static int countAsPath(final List<Segments> segments) {
136 // an AS_SET counts as 1, no matter how many ASs are in the set.
138 boolean setPresent = false;
139 for (final Segments s : segments) {
140 if (s.getCSegment() instanceof ASetCase) {
143 final AListCase list = (AListCase) s.getCSegment();
144 count += list.getAList().getAsSequence().size();
147 return (setPresent) ? ++count : count;
150 private static AsNumber getPeerAs(final List<Segments> segments) {
151 if (segments.size() == 0) {
154 final AListCase first = (AListCase) segments.get(0).getCSegment();
155 return first.getAList().getAsSequence().get(0).getAs();
159 public static int compareByteArrays(final byte[] byteOne, final byte[] byteTwo) {
160 for (int i = 0; i < byteOne.length; i++) {
161 final int res = Byte.compare(byteOne[i], byteTwo[i]);