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.path.attributes.Attributes;
19 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.path.attributes.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
26 * <a href="http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml">here</a>
29 public final class BGPObjectComparator implements Comparator<RIBEntryData<?, ?, ?>>, Serializable {
31 private static final long serialVersionUID = 3299599519482155374L;
33 private final AsNumber ourAS;
35 public BGPObjectComparator(final AsNumber ourAs) {
36 this.ourAS = Preconditions.checkNotNull(ourAs);
40 public int compare(final RIBEntryData<?, ?, ?> newObject, final RIBEntryData<?, ?, ?> oldObject) {
41 if (newObject == oldObject) {
44 if (newObject == null) {
47 if (oldObject == null) {
51 final Attributes newPath = newObject.getAttributes();
52 final Attributes oldPath = oldObject.getAttributes();
53 if (newPath.equals(oldPath) && Arrays.equals(newObject.getPeer().getRawIdentifier(), oldObject.getPeer().getRawIdentifier())) {
57 // 1. prefer path with accessible nexthop
58 // - we assume that all nexthops are accessible
60 // 2. prefer path with higher LOCAL_PREF
61 if ((newPath.getLocalPref() != null || oldPath.getLocalPref() != null)
62 && (newPath.getLocalPref() != null && !newPath.getLocalPref().equals(oldPath.getLocalPref()))) {
63 return newPath.getLocalPref().getPref().compareTo(oldPath.getLocalPref().getPref());
66 // 3. prefer learned path
67 // - we assume that all paths are learned
69 // 4. prefer the path with the shortest AS_PATH.
70 if (!newPath.getAsPath().equals(oldPath.getAsPath())) {
71 final Integer i1 = countAsPath(newPath.getAsPath().getSegments());
72 final Integer i2 = countAsPath(oldPath.getAsPath().getSegments());
73 return i2.compareTo(i1);
76 // 5. prefer the path with the lowest origin type
77 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
78 if (!newPath.getOrigin().equals(oldPath.getOrigin())) {
79 if (newPath.getOrigin().getValue().equals(BgpOrigin.Igp)) {
82 if (oldPath.getOrigin().getValue().equals(BgpOrigin.Igp)) {
85 if (newPath.getOrigin().getValue().equals(BgpOrigin.Egp)) {
92 // 6. prefer the path with the lowest multi-exit discriminator (MED)
93 if ((newPath.getMultiExitDisc() != null || oldPath.getMultiExitDisc() != null)
94 && (newPath.getMultiExitDisc() != null && !newPath.getMultiExitDisc().equals(oldPath.getMultiExitDisc()))) {
95 return oldPath.getMultiExitDisc().getMed().compareTo(newPath.getMultiExitDisc().getMed());
98 // 7. prefer eBGP over iBGP paths
99 // EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System).
100 final AsNumber first = getPeerAs(newPath.getAsPath().getSegments());
101 final AsNumber second = getPeerAs(oldPath.getAsPath().getSegments());
102 if ((first != null || second != null) && (first != null && !first.equals(second))) {
103 if (first.equals(this.ourAS)) {
106 if (second == null || second.equals(this.ourAS)) {
111 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
112 // - no next hop metric is advertized
114 // 9. When both paths are external, prefer the path that was received first (the oldest one).
115 // if (first.equals(this.ourAS) && second.equals(this.ourAS)) {
116 // FIXME: do we have a way how to determine which one was received first?
118 // 10. Prefer the route that comes from the BGP router with the lowest router ID.
119 // The router ID is the highest IP address on the router, with preference given to loopback addresses.
120 // If a path contains route reflector (RR) attributes, the originator ID is substituted for the router ID in the
121 // path selection process.
123 // RFC5004 states that this algorithm should end here and select existing path over new path in the
124 // best path selection process. Benefits are listed in the RFC: @see http://tools.ietf.org/html/rfc500
125 // - This algorithm SHOULD NOT be applied when either path is from a BGP Confederation peer.
126 // - not applicable, we don't deal with confederation peers
127 // - 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).
128 // - not applicable, BUG-2631 prevents parallel sessions to be created.
133 private static int countAsPath(final List<Segments> segments) {
134 // an AS_SET counts as 1, no matter how many ASs are in the set.
136 boolean setPresent = false;
137 for (final Segments s : segments) {
138 if (s.getCSegment() instanceof ASetCase) {
141 final AListCase list = (AListCase) s.getCSegment();
142 count += list.getAList().getAsSequence().size();
145 return (setPresent) ? ++count : count;
148 private static AsNumber getPeerAs(final List<Segments> segments) {
149 if (segments.size() == 0) {
152 final AListCase first = (AListCase) segments.get(0).getCSegment();
153 return first.getAList().getAsSequence().get(0).getAs();
157 public static int compareByteArrays(final byte[] byteOne, final byte[] byteTwo) {
158 for (int i = 0; i < byteOne.length; i++) {
159 final int res = Byte.compare(byteOne[i], byteTwo[i]);